

###Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions|Oliver Schebaum,Volker Drewello,Alexander Auge,Günter Reiss,Markus Münzenberg,Henning Schuhmann,Michael Seibt,Andy Thomas###

Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions. Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B
magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia,
and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance
ratios we found were 73% for alumina and 323% for magnesia-based tunnel
junctions. Additionally, tunnel junctions with a unified layer stack were
prepared for the three different barriers. In these systems, the tunnel
magnetoresistance ratios at optimum annealing temperatures were found to be 65%
for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The
similar tunnel magnetoresistance ratios of the tunnel junctions containing
alumina provide evidence that coherent tunneling is suppressed by the alumina
layer in the composite tunnel barrier.

###Tunneling anisotropic magnetoresistance driven by magnetic phase transition|X. Z. Chen,J. F. Feng,Z. C. Wang,J. Zhang,X. Y. Zhong,C. Song,L. Jin,B. Zhang,F. Li,M. Jiang,Y. Z. Tan,X. J. Zhou,G. Y. Shi,X. F. Zhou,X. D. Han,S. C. Mao,Y. H. Chen,X. F. Han,F. Pan###

Tunneling anisotropic magnetoresistance driven by magnetic phase transition. The independent control of two magnetic electrodes and spin-coherent
transport in magnetic tunnel junctions are strictly required for tunneling
magnetoresistance, while junctions with only one ferromagnetic electrode
exhibit tunneling anisotropic magnetoresistance dependent on the anisotropic
density of states with no room temperature performance so far. Here we report
an alternative approach to obtaining tunneling anisotropic magnetoresistance in
alfa-FeRh-based junctions driven by the magnetic phase transition of alfa-FeRh
and resultantly large variation of the density of states in the vicinity of MgO
tunneling barrier, referred to as phase transition tunneling anisotropic
magnetoresistance. The junctions with only one alfa-FeRh magnetic electrode
show a magnetoresistance ratio up to 20% at room temperature. Both the polarity
and magnitude of the phase transition tunneling anisotropic magnetoresistance
can be modulated by interfacial engineering at the alfa-FeRh/MgO interface.
Besides the fundamental significance, our finding might add a different
dimension to magnetic random access memory and antiferromagnet spintronics.

###Enhanced magneto-transport at high bias in quasi-magnetic tunnel junctions with EuS spin-filter barriers|T. Nagahama,T. S. Santos,J. S. Moodera###

Enhanced magneto-transport at high bias in quasi-magnetic tunnel junctions with EuS spin-filter barriers. In quasi-magnetic tunnel junctions (QMTJs) with a EuS spin filter tunnel
barrier between Al and Co electrodes, we observed large magnetoresistance (MR).
The bias dependence shows an abrupt increase of MR ratio in high bias voltage,
which is contrary to conventional magnetic tunnel junctions (MTJs). This
behavior can be understood as due to Fowler-Nordheim tunneling through the
fully spin-polarized EuS conduction band. The I-V characteristics and bias
dependence of MR calculated using tunneling theory shows excellent agreement
with experiment.

###Tunnel magnetoresistance and interfacial electronic state|J. Inoue,H. Itoh###

Tunnel magnetoresistance and interfacial electronic state. We study the relation between tunnel magnetoresistance (TMR) and interfacial
electronic states modified by magnetic impurities introduced at the interface
of the ferromagnetic tunnel junctions, by making use of the periodic Anderson
model and the linear response theory. It is indicated that the TMR ratio is
strongly reduced depending on the position of the $d$-levels of impurities,
based on reduction in the spin-dependent $s$-electron tunneling in the majority
spin state. The results are compared with experimental results for Cr-dusted
ferromagnetic tunnel junctions, and also with results for metallic multilayers
for which similar reduction in giant magnetoresistance has been reported.

###Gigantic tunneling magnetoresistance in magnetic Weyl semimetal tunnel junctions|D. J. P. de Sousa,C. O. Ascencio,P. M. Haney,J. P. Wang,Tony Low###

Gigantic tunneling magnetoresistance in magnetic Weyl semimetal tunnel junctions. We investigate the tunneling magnetoresistance in magnetic tunnel junctions
(MTJs) comprised of Weyl semimetal contacts. We show that
chirality-magnetization locking leads to a gigantic tunneling magnetoresistance
ratio, an effect that does not rely on spin filtering by the tunnel barrier.
Our results indicate that the conductance in the anti-parallel configuration is
more sensitive to magnetization fluctuations than in MTJs with normal
ferromagnets, and predicts a TMR as large as 10^4 % when realistic
magnetization fluctuations are accounted for. In addition, we show that the
Fermi arc states give rise to a non-monotonic dependence of conductance on the
misalignment angle between the magnetizations of the two contacts.

###Spin polarized tunneling in MgO-based tunnel junctions with superconducting electrodes|Oliver Schebaum,Jagadeesh S. Moodera,Andy Thomas###

Spin polarized tunneling in MgO-based tunnel junctions with superconducting electrodes. We prepared magnetic tunnel junctions with one ferromagnetic and one
superconducting Al-Si electrode. Pure cobalt electrodes were compared with a
Co-Fe-B alloy and the Heusler compound Co2FeAl. The polarization of the
tunneling electrons was determined using the Maki-Fulde-model and is discussed
along with the spin-orbit scattering and the total pair-breaking parameters.
The junctions were post-annealed at different temperatures to investigate the
symmetry filtering mechanism responsible for the giant tunneling
magnetoresistance ratios in Co-Fe-B/ MgO/ Co-Fe-B junctions.

###Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance|Mengxing Wang,Wenlong Cai,Kaihua Cao,Jiaqi Zhou,Jerzy Wrona,Shouzhong Peng,Huaiwen Yang,Jiaqi Wei,Wang Kang,Youguang Zhang,Jürgen Langer,Berthold Ocker,Albert Fert,Weisheng Zhao###

Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance. Perpendicular magnetic tunnel junctions based on MgO/CoFeB structures are of
particular interest for magnetic random-access memories because of their
excellent thermal stability, scaling potential, and power dissipation. However,
the major challenge of current-induced switching in the nanopillars with both a
large tunnel magnetoresistance ratio and a low junction resistance is still to
be met. Here, we report spin transfer torque switching in nano-scale
perpendicular magnetic tunnel junctions with a magnetoresistance ratio up to
249% and a resistance area product as low as 7.0 {\Omega}.{\mu}m2, which
consists of atom-thick W layers and double MgO/CoFeB interfaces. The efficient
resonant tunnelling transmission induced by the atom-thick W layers could
contribute to the larger magnetoresistance ratio than conventional structures
with Ta layers, in addition to the robustness of W layers against high
temperature diffusion during annealing. The switching critical current density
could be lower than 3.0 MA.cm-2 for devices with a 45 nm radius.

###Ab initio description of tunnel junctions|Peter Zahn,Ingrid Mertig###

Ab initio description of tunnel junctions. Based on spin-density functional theory we calculate the electronic structure
of a tunnel junction consisting of two magnetic Fe layers separated by an
insulating vacuum barrier selfconsistently. For the conductance the Landauer
formula is evaluated in the ballistic limit as function of the magnetic
configuration. Based on these conductances the tunnel magnetoresistance (TMR)
ratio is obtained. We investigate the relation between TMR ratio and spin
polarization of the electronic structure at the metal/insulator interface.

###The Effects of Resonant Tunneling on Magnetoresistance through a Q uantum Dot|Tetsufumi Tanamoto,Shinobu Fujita###

The Effects of Resonant Tunneling on Magnetoresistance through a Q uantum Dot. The effect of resonant tunneling on magnetoresistance (MR) is studied
theoretically in a double junction system. We have found that the ratio of the
MR of the resonant peak current is reduced more than that of the single
junction, whereas that of the valley current is enhanced depending on the
change of the discrete energy-level under the change of magnetic field. We also
found that the peak current-valley current (PV) ratio decreases when the
junction conductance increases.

###A ferromagnetic oxide semiconductor as spin injection electrode in magnetic tunnel junction|H. Toyosaki,T. Fukumura,K. Ueno,M. Nakano,M. Kawasaki###

A ferromagnetic oxide semiconductor as spin injection electrode in magnetic tunnel junction. A magnetic tunnel junctions composed of room temperature ferromagnetic
semiconductor rutile Ti1-xCoxO2-d and ferromagnetic metal Fe0.1Co0.9 separated
by AlOx barrier showed positive tunneling magnetoresistance (TMR) with a ratio
of ~11 % at 15 K, indicating that Ti1-xCoxO2-d can be used as a spin injection
electrode. The TMR decreased with increasing temperature and vanished above 180
K. TMR action at high temperature is likely prohibited by the inelastic
tunneling conduction due to the low quality of the amorphous barrier layer
and/or the junction interface.

###High TMR ratio in Co2FeSi and Fe2CoSi based magnetic tunnel junctions|Christian Sterwerf,Markus Meinert,Jan-Michael Schmalhorst,Günter Reiss###

High TMR ratio in Co2FeSi and Fe2CoSi based magnetic tunnel junctions. Magnetic tunnel junctions with Fe1+xCo2-xSi (0 < x < 1) electrodes and MgO
barrier were prepared on MgO substrates by magnetron co-sputtering. Maximum
tunnel magnetoresistance (TMR) ratios of 262 % at 15 K and 159 % at room
temperature were observed for x=0.75. Correlations of the annealing temperature
dependent atomic ordering and TMR amplitude are discussed. The high TMR for an
intermediate stoichiometry is ascribed to the adjustment of the Fermi energy
within a minority spin pseudo gap.

###Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier|Matthias Althammer,Amit Vikam Singh,Sahar Keshavarz,Mehmet Kenan Yurtisigi,Rohan Mishra,Albina Borisevich,Patrick LeClair,Arunava Gupta###

Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier. We experimentally investigate the structural, magnetic and electrical
transport properties of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ based magnetic tunnel
junctions with a SrSnO$_3$ barrier. Our results show that despite the large
number of defects in the strontium stannate barrier, due to the large lattice
mismatch, the observed tunnel magnetoresistance is comparable to tunnel
junctions with a better lattice matched STiO$_3$ barrier, reaching values of up
to 350% at T=5 K. Further analysis of the current-voltage characteristics of
the junction and the bias voltage dependence of the observed tunnel
magnetoresistance show a decrease of the TMR with increasing bias voltage. In
addition, the observed TMR vanishes for T>200 K. Our results suggest that by
employing a better lattice matched ferromagnetic electrode and thus reducing
the structural defects in the strontium stannate barrier even larger TMR ratios
might be possible in the future.

###Large Tunneling Anisotropic Magneto-Seebeck Effect in a CoPt|MgO|Pt Tunnel Junction|V. P. Amin,J. Zemen,J. Železný,T. Jungwirth,Jairo Sinova###

Large Tunneling Anisotropic Magneto-Seebeck Effect in a CoPt|MgO|Pt Tunnel Junction. We theoretically investigate the Tunneling Anisotropic Magneto-Seebeck effect
in a realistically-modeled CoPt|MgO|Pt tunnel junction using coherent transport
calculations. For comparison we study the tunneling magneto-Seebeck effect in
CoPt|MgO|CoPt as well. We find that the magneto-Seebeck ratio of CoPt|MgO|Pt
exceeds that of CoPt|MgO|CoPt for small barrier thicknesses, reaching 175% at
room temperature. This result provides a sharp contrast to the
magnetoresistance, which behaves oppositely for all barrier thicknesses and
differs by one order of magnitude between devices. Here the magnetoresistance
results from differences in transmission brought upon by changing the tunnel
junction's magnetization configuration. The magneto-Seebeck effect results from
variations in asymmetry of the energy-dependent transmission instead. We report
that this difference in origin allows for CoPt|MgO|Pt to possess strong thermal
magnetic-transport anisotropy.

###Impact of a ferromagnetic insulating barrier in magnetic tunnel junctions|M. Abbasi Eskandari,S. Ghotb,P. Fournier###

Impact of a ferromagnetic insulating barrier in magnetic tunnel junctions. We investigate spin-dependent conductance across a magnetic tunnel junction
(MTJ) including a ferromagnetic insulating barrier. The MTJ consists of two
half-metallic ferromagnetic La2/3Sr1/3MnO3 (LSMO) manganites as electrodes and
La2NiMnO6 (LNMO) double perovskite as a ferromagnetic insulating barrier. The
resistance of the junction is strongly dependent not only on the orientation of
the magnetic moments in LSMO electrodes, but also on the direction of the
magnetization of the LNMO barrier with respect to that of LSMO. The ratio of
tunnel magnetoresistance reaches a maximum value of 24% at 10 K, and it
decreases with temperature until it completely disappears above the critical
temperature of LNMO at 280 K. The tunneling process is described using a
mechanism which involves both empty and filled eg states of the LNMO barrier
acting as a spin-filter. A magnetic insulating barrier is an interesting path
for achieving room temperature magnetoresistance in oxide-based
heterostructures.

###Superpoissonian shot noise in organic magnetic tunnel junctions|Juan Pedro Cascales,Jhen-Yong Hong,Isidoro Martinez,Minn-Tsong Lin,Tomasz Szczepanski,Vitalii K. Dugaev,Jozef Barnas,Farkad G. Aliev###

Superpoissonian shot noise in organic magnetic tunnel junctions. Organic molecules have recently revolutionized ways to create new spintronic
devices. Despite intense studies, the statistics of tunneling electrons through
organic barriers remains unclear. Here we investigate conductance and shot
noise in magnetic tunnel junctions with PTCDA barriers a few nm thick. For
junctions in the electron tunneling regime, with magnetoresistance ratios
between 10 and 40\%, we observe superpoissonian shot noise. The Fano factor
exceeds in 1.5-2 times the maximum values reported for magnetic tunnel
junctions with inorganic barriers, indicating spin dependent bunching in
tunneling. We explain our main findings in terms of a model which includes
tunneling through a two level (or multilevel) system, originated from
interfacial bonds of the PTCDA molecules. Our results suggest that interfaces
play an important role in the control of shot noise when electrons tunnel
through organic barriers.

###Tunneling magnetoresistance in diluted magnetic semiconductor tunnel junctions|Pin Lyu,Kyungsun Moon###

Tunneling magnetoresistance in diluted magnetic semiconductor tunnel junctions. Using the spin-polarized tunneling model and taking into account the basic
physics of ferromagnetic semiconductors, we study the temperature dependence of
the tunneling magnetoresistance (TMR) in the diluted magnetic semiconductor
(DMS) trilayer heterostructure system (Ga,Mn)As/AlAs/(Ga,Mn)As. The
experimentally observed TMR ratio is in reasonable agreement with our result
based on the typical material parameters. It is also shown that the TMR ratio
has a strong dependence on both the itinerant-carrier density and the magnetic
ion density in the DMS electrodes. This can provide a potential way to achieve
larger TMR ratio by optimally adjusting the material parameters.

###Room temperature tunneling anisotropic and collinear magnetoresistance|A. N. Grigorenko,K. S. Novoselov,D. J. Mapps###

Room temperature tunneling anisotropic and collinear magnetoresistance. We report a room temperature tunneling anisotropic magnetoresistance in
Co/Al2O3/NiFe junctions containing magnetic electrodes oxidized prior to
forming the Al2O3 layer. A significant change in a tunnel magnetoresistance is
observed when the layer magnetizations are rotated collinearly in the junction
plane by an applied external field. The angular dependence of the tunneling
anisotropic magnetoresistance could be explained by the presence of an
antiferromagnetic oxide layer formed within the barrier.

###Tunnel magnetoresistance of Fe3O4/MgO/Fe nanostructures|S. G. Chigarev,E. M. Epshtein,I. V. Malikov,G. M. Mikhailov,P. E. Zilberman###

Tunnel magnetoresistance of Fe3O4/MgO/Fe nanostructures. A magnetic tunnel junction Fe3O4/MgO/Fe with (001) layer orientation is
considered. The junction magnetic energy is analyzed as a function of the angle
between the layer magnetization vectors under various magnetic fields. The
tunnel magnetoresistance is calculated as a function of the external magnetic
field. In contrast with junctions with unidirectional anisotropy, a
substantially lower magnetic field is required for the junction switching.

###Large inverse tunneling magnetoresistance in Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al/MgO/CoFe magnetic tunnel junctions|A. D. Rata,H. Braak,D. E. Buergler,C. M. Schneider###

Large inverse tunneling magnetoresistance in Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al/MgO/CoFe magnetic tunnel junctions. Magnetic tunnel junctions with the layer sequence
Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al/MgO/CoFe were fabricated by magnetron sputtering
at room temperature (RT). The samples exhibit a large inverse tunneling
magnetoresistance (TMR) effect of up to -66% at RT. The largest value of -84%
at 20 K reflects a rather weak influence of temperature. The dependence on the
voltage drop shows an unusual behavior with two almost symmetric peaks at
$\pm600$ mV with large inverse TMR ratios and small positive values around zero
bias.

###Dependence of tunnel magnetoresistance in MgO based magnetic tunnel junctions on Ar pressure during MgO sputtering|Shoji Ikeda,Jun Hayakawa,Young Min Lee,Ryutaro Sasaki,Toshiyasu Meguro,Fumihiro Matsukura,Hideo Ohno###

Dependence of tunnel magnetoresistance in MgO based magnetic tunnel junctions on Ar pressure during MgO sputtering. We investigated dependence of tunnel magnetoresistance effect in
CoFeB/MgO/CoFeB magnetic tunnel junctions on Ar pressure during MgO-barrier
sputtering. Sputter deposition of MgO-barrier at high Ar pressure of 10 mTorr
resulted in smooth surface and highly (001) oriented MgO. Using this MgO as a
tunnel barrier, tunnel magnetoresistance (TMR) ratio as high as 355% at room
temperature (578% at 5K) was realized after annealing at 325 C or higher, which
appears to be related to a highly (001) oriented CoFeB texture promoted by the
smooth and highly oriented MgO. Electron-beam lithography defined
deep-submicron MTJs having a low-resistivity Au underlayer with the
high-pressure deposited MgO showed high TMR ratio at low resistance-area
product (RA) below 10 ohm-um^2 as 27% at RA = 0.8 ohm-um^2, 77% at RA = 1.1
ohm-um^2, 130% at RA = 1.7 ohm-um^2, and 165% at RA = 2.9 ohm-um^2.

###Tunnel magnetoresistance in scandium nitride magnetic tunnel junctions using first principles|Suyogya Karki,Vivian Rogers,Priyamvada Jadaun,Daniel S. Marshall,Jean Anne C. Incorvia###

Tunnel magnetoresistance in scandium nitride magnetic tunnel junctions using first principles. The magnetic tunnel junction is a cornerstone of spintronic devices and
circuits, providing the main way to convert between magnetic and electrical
information. In state-of-the-art magnetic tunnel junctions, magnesium oxide is
used as the tunnel barrier between magnetic electrodes, providing a uniquely
large tunnel magnetoresistance at room temperature. However, the wide bandgap
and band alignment of magnesium oxide-iron systems increases the
resistance-area product and causes challenges of device-to-device variability
and tunnel barrier degradation under high current. Here, we study using first
principles narrower-bandgap scandium nitride tunneling properties and transport
in magnetic tunnel junctions in comparison to magnesium oxide. These
simulations demonstrate a high tunnel magnetoresistance in Fe/ScN/Fe MTJs via
{\Delta}_1 and {\Delta}_2' symmetry filtering with low wavefunction decay
rates, allowing a low resistance-area product. The results show that scandium
nitride could be a new tunnel barrier material for magnetic tunnel junction
devices to overcome variability and current-injection challenges.

###Tunneling Magnetoresistance in Junctions Composed of Ferromagnets and Time-Reversal Invariant Topological Superconductors|Zhongbo Yan,Shaolong Wan###

Tunneling Magnetoresistance in Junctions Composed of Ferromagnets and Time-Reversal Invariant Topological Superconductors. Tunneling Magnetoresistance between two ferrromagnets is an issue of
fundamental importance in spintronics. In this work, we show that tunneling
magnetoresistance can also emerge in junctions composed of ferromagnets and
time-reversal invariant topological superconductors without spin-rotation
symmetry. Here the physical origin is that when the spin-polarization direction
of injected electron from the ferromagnet lying in the same plane of the
spin-polarization direction of Majorana zero modes, the electron will undergo a
perfect spin-equal Andreev reflection, while injected electrons with other
spin-polarization direction will be partially Andreev reflected and partially
normal reflected, which consequently have a lower conductance, and therefore,
the magnetoresistance effect emerges. Compared to conventional magnetic tunnel
junctions, an unprecedented advantage of the junctions studied here is that
arbitrary high tunneling magnetoresistance can be obtained even the
magnetization of the ferromagnets are weak and the insulating tunneling
barriers are featureless. Our findings provide a new fascinating mechanism to
obtain high tunneling magnetoresistance.

###Quasi-reversible Magnetoresistance in Exchange Spring Tunnel Junctions|M. Zhu,M. J. Wilson,P. Mitra,P. Schiffer,N. Samarth###

Quasi-reversible Magnetoresistance in Exchange Spring Tunnel Junctions. We report a large, quasi-reversible tunnel magnetoresistance in
exchange-biased ferromagnetic semiconductor tunnel junctions wherein a soft
ferromagnetic semiconductor (\gma) is exchange coupled to a hard ferromagnetic
metal (MnAs). Our observations are consistent with the formation of a region of
inhomogeneous magnetization (an "exchange spring") within the biased \gma
layer. The distinctive tunneling anisotropic magnetoresistance of \gma produces
a pronounced sensitivity of the magnetoresistance to the state of the exchange
spring.

###Spin-polarized transport in magnetic tunnel junctions with ZnTe barriers|W. G. Wang,C. Ni,A. Ozbay,L. R. Shah,X. Fan,X. M. Kou,E. R. Nowak,J. Q. Xiao###

Spin-polarized transport in magnetic tunnel junctions with ZnTe barriers. Magnetic tunnel junctions with wide band gap semiconductor ZnTe barrier were
fabricated. A very low barrier height and sizable magnetoresistance were
observed in the Fe/ZnTe/Fe junctions at room temperature. The nonlinear I-V
characteristic curve confirmed the observed magnetoresistance is due to
spin-dependent tunneling effect. Temperature dependent study indicated that the
total conductance of the junction is dominated by direct tunneling, with only a
small portion from the hopping conduction through the defect states inside the
barrier.

###Magnetoresistance of atomic-scale electromigrated nickel nanocontacts|Z. K. Keane,L. H. Yu,D. Natelson###

Magnetoresistance of atomic-scale electromigrated nickel nanocontacts. We report measurements of the electron transport through atomic-scale
constrictions and tunnel junctions between ferromagnetic electrodes. Structures
are fabricated using a combination of e-beam lithography and controlled
electromigration. Sample geometries are chosen to allow independent control of
electrode bulk magnetizations. As junction size is decreased to the single
channel limit, conventional anisotropic magnetoresistance (AMR) increases in
magnitude, approaching the size expected for tunneling magnetoresistance (TMR)
upon tunnel junction formation. Significant mesoscopic variations are seen in
the magnitude and sign of the magnetoresistance, and no evidence is found of
large ballistic magnetoresistance effects.

###Tailoring tunnel magnetoresistance by ultrathin Cr and Co interlayers: A first-principles investigation of Fe/MgO/Fe junctions|P. Bose,P. Zahn,J. Henk,I. Mertig###

Tailoring tunnel magnetoresistance by ultrathin Cr and Co interlayers: A first-principles investigation of Fe/MgO/Fe junctions. We report on systematic ab-initio investigations of Co and Cr interlayers
embedded in Fe(001)/MgO/Fe(001) magnetic tunnel junctions, focusing on the
changes of the electronic structure and the transport properties with
interlayer thickness. The results of spin-dependent ballistic transport
calculations reveal options to specifically manipulate the tunnel
magnetoresistance ratio. The resistance area products and the tunnel
magnetoresistance ratios show a monotonous trend with distinct oscillations as
a function of the Cr thickness. These modulations are directly addressed and
interpreted by means of magnetic structures in the Cr films and by complex band
structure effects. The characteristics for embedded Co interlayers are
considerably influenced by interface resonances which are analyzed by the local
electronic structure.

###Anisotropic tunneling magnetoresistance and tunneling anisotropic magnetoresistance: spin-orbit coupling in magnetic tunnel junctions|Alex Matos-Abiague,Jaroslav Fabian###

Anisotropic tunneling magnetoresistance and tunneling anisotropic magnetoresistance: spin-orbit coupling in magnetic tunnel junctions. The effects of the spin-orbit interaction on the tunneling magnetoresistance
of ferromagnet/semiconductor/normal metal tunnel junctions are investigated.
Analytical expressions for the tunneling anisotropic magnetoresistance (TAMR)
are derived within an approximation in which the dependence of the
magnetoresistance on the magnetization orientation in the ferromagnet
originates from the interference between Bychkov-Rashba and Dresselhaus
spin-orbit couplings that appear at junction interfaces and in the tunneling
region. We also investigate the transport properties of
ferromagnet/semiconductor/ferromagnet tunnel junctions and show that in such
structures the spin-orbit interaction leads not only to the TAMR effect but
also to the anisotropy of the conventional tunneling magnetoresistance (TMR).
The resulting anisotropic tunneling magnetoresistance (ATMR) depends on the
absolute magnetization directions in the ferromagnets. Within the proposed
model, depending on the magnetization directions in the ferromagnets, the
interplay of Bychkov-Rashba and Dresselhaus spin-orbit couplings produces
differences between the rates of transmitted and reflected spins at the
ferromagnet/seminconductor interfaces, which results in an anisotropic local
density of states at the Fermi surface and in the TAMR and ATMR effects. Model
calculations for Fe/GaAs/Fe tunnel junctions are presented. Furthermore, based
on rather general symmetry considerations, we deduce the form of the
magnetoresistance dependence on the absolute orientations of the magnetizations
in the ferromagnets.

###Spin transport through a single self-assembled InAs quantum dot with ferromagnetic leads|K. Hamaya,S. Masubuchi,M. Kawamura,T. Machida,M. Jung,K. Shibata,K. Hirakawa,T. Taniyama,S. Ishida,Y. Arakawa###

Spin transport through a single self-assembled InAs quantum dot with ferromagnetic leads. We have fabricated a lateral double barrier magnetic tunnel junction (MTJ)
which consists of a single self-assembled InAs quantum dot (QD) with
ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance
(TMR) effect, which is evidence for spin transport through a single
semiconductor QD. The TMR ratio and the curve shapes are varied by changing the
gate voltage.

###Effect of Image Potential on Spin Polarized Transport through Magnetic Tunnel Junctions|Tehseen Zahra Raza,Hassan Raza###

Effect of Image Potential on Spin Polarized Transport through Magnetic Tunnel Junctions. We study the effect of image potential on spin polarized transport through
Fe/MgO/Fe magnetic tunnel junctions in the presence of symmetry filtering. The
image potential is included within the Simmon's model coupled with the
non-equilibrium Green's function formalism to calculate the quantum transport.
The increase in the current densities for the $\Delta_1$ symmetry and the
$\Delta_5$ symmetry bands due to the image potential is more pronounced at
higher bias, whereas, the increase in the magnitude of the tunnel
magnetoresistance ratio is more prominent at lower bias for various barrier
thicknesses.

###Nearly total spin polarization in La2/3Sr1/3MnO3 from tunneling experiments|M. Bowen,M. Bibes,A. Barthelemy,J. -P. Contour,A. Anane,Y. Lemaitre,A. Fert###

Nearly total spin polarization in La2/3Sr1/3MnO3 from tunneling experiments. We have performed magnetotransport measurements on La2/3Sr1/3MnO3 / SrTiO3 /
La2/3Sr1/3MnO3 magnetic tunnel junctions. A magnetoresistance ratio of more
than 1800 % is obtained at 4K, from which we infer an electrode spin
polarization of at least 95 %. This result strongly underscores the
half-metallic nature of mixed-valence manganites and demonstrates its
capability as a spin analyzer. The magnetoresistance extends up to temperatures
of more than 270K. We argue that these improvements over most previous works
may result from optimizing the patterning process for oxide heterostructures.

###Observation of plateau-like magnetoresistance in twisted Fe3GeTe2/Fe3GeTe2 junction|Junghyun Kim,Suhan Son,Matthew. J. Coak,Inho Hwang,Youjin Lee,Kaixuan Zhang,Je-Geun Park###

Observation of plateau-like magnetoresistance in twisted Fe3GeTe2/Fe3GeTe2 junction. Controlling the stacking of van der Waals (vdW) materials is found to produce
exciting new findings, since hetero- or homo- structures have added the diverse
possibility of assembly and manipulated functionalities. However, so far, the
homostructure with a twisted angle based on the magnetic vdW materials remains
unexplored. Here, we achieved a twisted magnetic vdW Fe3GeTe2/Fe3GeTe2 junction
with broken crystalline symmetry. A clean and metallic vdW junction is
evidenced by the temperature-dependent resistance and the linear I-V curve.
Unlike the pristine FGT, a plateau-like magnetoresistance (PMR) is observed in
the magnetotransport of our homojunction due to the antiparallel magnetic
configurations of the two FGT layers. The PMR ratio is found to be ~0.05% and
gets monotonically enhanced as temperature decreases like a metallic giant
magnetoresistance (GMR). Such a tiny PMR ratio is at least three orders of
magnitude smaller than the tunneling magnetoresistance (TMR) ratio, justifying
our clean metallic junction without a spacer. Our findings demonstrate the
feasibility of the controllable homostructure and shed light on future
spintronics using magnetic vdW materials.

###Dependence of tunnel magnetoresistance on ferromagnetic electrode materials in MgO-barrier magnetic tunnel junctions|Shoji Ikeda,Jun Hayakawa,Young Min Lee,Fumihiro Matsukura,Hideo Ohno###

Dependence of tunnel magnetoresistance on ferromagnetic electrode materials in MgO-barrier magnetic tunnel junctions. We investigated the relationship between the tunnel magnetoresistance (TMR)
ratio and the electrode structure in MgO-barrier magnetic tunnel junctions
(MTJs). The TMR ratio in a MTJ with Co40Fe40B20 reference and free layers
reached 355% at the post-deposition annealing temperature of Ta=400 degree C.
When Co50Fe50 or Co90Fe10 is used for the reference layer material, no high TMR
ratio was observed. The key to have high TMR ratio is to have highly oriented
(001) MgO barrier/CoFeB crystalline electrodes. The highest TMR ratio obtained
so far is 450% at Ta = 450 degree C in a pseudo spin-valve MTJ.

###Giant thermoelectric effect in Al2O3 magnetic tunnel junctions|Weiwei Lin,Michel Hehn,Laurent Chaput,Béatrice Negulescu,Stéphane Andrieu,François Montaigne,Stéphane Mangin###

Giant thermoelectric effect in Al2O3 magnetic tunnel junctions. Thermoelectric effects in magnetic nanostructures and the so-called spin
caloritronics are attracting much interest. Indeed it provides a new way to
control and manipulate spin currents which are key elements of spin-based
electronics. Here we report on giant magnetothermoelectric effect in Al2O3
magnetic tunnel junctions. The thermovoltage in this geometry can reach 1 mV.
Moreover a magneto-thermovoltage effect could be measured with ratio similar to
the tunnel magnetoresistance ratio. The Seebeck coefficient can then be tuned
by changing the relative magnetization orientation of the two magnetic layers
in the tunnel junction. Therefore our experiments extend the range of
spintronic devices application to thermoelectricity and provide a crucial piece
of information for understanding the physics of thermal spin transport.

###Biaxial strain effect of spin dependent tunneling in MgO magnetic tunnel junctions|Ajeesh M. Sahadevan,Ravi K. Tiwari,Gopinadhan Kalon,Charanjit S. Bhatia,Mark Saeys,Hyunsoo Yang###

Biaxial strain effect of spin dependent tunneling in MgO magnetic tunnel junctions. We study the effect of strain on magnetic tunnel junctions (MTJ) induced by a
diamond like carbon (DLC) film. The junction resistance as well as the tunnel
magnetoresistance (TMR) reduces with the DLC film. Non-equilibrium Green's
function quantum transport calculations show that the application of biaxial
strain increases the conductance for both the parallel and anti-parallel
configurations. However, the conductance for the minority channel and for the
anti-parallel configuration is significantly more sensitive to strain, which
drastically increases transmission through a MgO tunnel barrier, therefore, the
TMR ratio decreases with biaxial strain.

###Correlation of tunnel magnetoresistance with the magnetic properties in perpendicular CoFeB-based junctions with exchange bias|Orestis Manos,Panagiota Bougiatioti,Denis Dyck,Torsten Huebner,Karsten Rott,Jan-Michael Schmalhorst,Günter Reiss###

Correlation of tunnel magnetoresistance with the magnetic properties in perpendicular CoFeB-based junctions with exchange bias. We investigate the dependence of magnetic properties on the post-annealing
temperature/time, the thickness of soft ferromagnetic electrode and Ta dusting
layer in the pinned electrode as well as their correlation with the tunnel
magnetoresistance ratio, in a series of perpendicular magnetic tunnel junctions
of materials sequence
Ta/Pd/IrMn/CoFe/Ta$(\textit{x})$/CoFeB/MgO$(\textit{y})$/CoFeB$(\textit{z})$/Ta/Pd.
We obtain a large perpendicular exchange bias of 79.6$\,$kA/m for $x=0.3\,$nm.
For stacks with $z=1.05\,$nm, the magnetic properties of the soft electrode
resemble the characteristics of superparamagnetism. For stacks with
$x=0.4\,$nm, $y=2\,$nm, and $z=1.20\,$nm, the exchange bias presents a
significant decrease at post annealing temperature
$T_\textrm{ann}=330\,^{\circ}$C for 60 min, while the interlayer exchange
coupling and the saturation magnetization per unit area sharply decay at
$T_\textrm{ann}=340\,^{\circ}$C for 60 min. Simultaneously, the tunnel
magnetoresistance ratio shows a peak of $65.5\%$ after being annealed at
$T_\textrm{ann}=300\,^{\circ}$C for 60 min, with a significant reduction down
to $10\%$ for higher annealing temperatures
($T_\textrm{ann}\geq330\,^{\circ}$C) and down to $14\%$ for longer annealing
times ($T_\textrm{ann}=300\,^{\circ}$C for 90 min). We attribute the large
decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the
pinned electrode.

###Low Voltage I-V Characteristics in Magnetic Tunnel Junctions|G. G. Cabrera,N. Garcia###

Low Voltage I-V Characteristics in Magnetic Tunnel Junctions. We show that elastic currents that take into account variations of the tunnel
transmitivity with voltage and a large ratio of majority to minority spin
densities of states of the $s$ band, can account for the low voltage current
anomalies observed in magnet-oxide-magnet junctions. The anomalies can be
positive, negative or have a mixed form, depending of the position of the Fermi
level in the $s$ band, in agreement with observations. Magnon contribution is
negligible small to account for the sharp drop of the magnetoresistance with
the voltage bias.

###Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer|Young Min Lee,Jun Hayakawa,Shoji Ikeda,Fumihiro Matsukura,Hideo Ohno###

Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer. We investigated the relationship between tunnel magnetoresistance (TMR) ratio
and the crystallization of CoFeB layers through annealing in magnetic tunnel
junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet
pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased
with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C,
whereas the TMR ratio of the MTJs with pinned layers without Ru spacers
decreased at Ta over 325C. Ruthenium spacers play an important role in forming
an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through
annealing at high temperatures.

###Sub-Poissonian shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions|Tomonori Arakawa,Koji Sekiguchi,Shuji Nakamura,Kensaku Chida,Yoshitaka Nishihara,Daichi Chiba,Kensuke Kobayashi,Akio Fukushima,Shinji Yuasa,Teruo Ono###

Sub-Poissonian shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions. We measured the shot noise in the CoFeB/MgO/CoFeB-based magnetic tunneling
junctions with a high tunneling magnetoresistance ratio (over 200% at 3 K).
Although the Fano factor in the anti-parallel configuration is close to unity,
it is observed to be typically 0.91\pm0.01 in the parallel configuration. It
indicates the sub-Poissonian process of the electron tunneling in the parallel
configuration due to the relevance of the spin-dependent coherent transport in
the low bias regime.

###Surface Acoustic Wave induced modulation of tunneling magnetoresistance in magnetic tunnel junctions|Dhritiman Bhattacharya,Peng Sheng,Md Ahsanul Abeed,Zhengyang Zhao,Hongshi Li,Jian-Ping Wang,Supriyo Bandyopadhyay,Bin Ma,Jayasimha Atulasimha###

Surface Acoustic Wave induced modulation of tunneling magnetoresistance in magnetic tunnel junctions. We show that a surface acoustic wave (SAW) applied across the terminals of a
magnetic tunnel junction (MTJ) decreases both the (time-averaged) parallel and
antiparallel resistances of the MTJ, with the latter decreasing much more than
the former. This results in a decrease of the tunneling magnetoresistance (TMR)
ratio. The coercivities of the free and fixed layer of the MTJ, however, are
not affected significantly, suggesting that the SAW does not cause large-angle
magnetization rotation in the magnetic layers through the inverse
magnetostriction (Villari) effect at the power levels used. This study sheds
light on the dynamical behavior of an MTJ under periodic compressive and
tensile strain.

###Spin-orbit induced anisotropy in the tunneling magnetoresistance of magnetic tunnel junctions|A. Matos-Abiague,J. Fabian###

Spin-orbit induced anisotropy in the tunneling magnetoresistance of magnetic tunnel junctions. The effects of the spin-orbit interaction on the tunneling magnetoresistance
of magnetic tunnel junctions are investigated. A model in which the
experimentally observed two-fold symmetry of the anisotropic tunneling
magnetoresistance (TAMR) originates from the interference between Dresselhaus
and Bychkov-Rashba spin-orbit couplings is formulated. Bias induced changes of
the Bychkov-Rashba spin-orbit coupling strength can result in an inversion of
the TAMR. The theoretical calculations are in good agreement with the TAMR
experimentally observed in epitaxial Fe/GaAs/Au tunnel junctions.

###Enhanced magnetoresistance in perpendicular magnetic tunneling junctions with MgAl2O4 barrier|Pravin Khanal,Bowei Zhou,Magda Andrade,Christopher Mastrangelo,Ali Habiboglu,Arthur Enriquez,Daulton Fox,Kennedy Warrilow,Wei-Gang Wang###

Enhanced magnetoresistance in perpendicular magnetic tunneling junctions with MgAl2O4 barrier. Perpendicular magnetic tunnel junction with MgAl2O4 barrier is investigated.
It is found that reactive RF sputtering with O2 is essential to obtain strong
perpendicular magnetic anisotropy and large tunneling magnetoresistance in
MgAl2O4-based junctions. An interfacial perpendicular magnetic anisotropy
energy density of 2.25 mJ/m2 is obtained for the samples annealed at 400C. An
enhanced magnetoresistance of 60% has also been achieved. The Vhalf, bias
voltage at which tunneling magnetoresistance drops to half of the zero-bias
value, is found to be about 1V, which is substantially higher than that of
MgO-based junctions.

###Diffusive model of current-in-plane-tunneling in double magnetic tunnel junctions|Pierre-Yves Clément,Clarisse Ducruet,Claire Baraduc,Mair Chshiev,Bernard Diény###

Diffusive model of current-in-plane-tunneling in double magnetic tunnel junctions. We propose a model that describes current-in-plane tunneling transport in
double barrier magnetic tunnel junctions in diffusive regime. Our study shows
that specific features appear in double junctions that are described by
introducing two typical length scales. The model may be used to measure the
magnetoresistance and the resistance area product of both barriers in
unpatterned stacks of double barrier magnetic tunnel junctions.

###Pinhole and tunneling conduction channels superimposed in magnetic tunnel junction: results and inferences|Soumik Mukhopadhyay,I. Das###

Pinhole and tunneling conduction channels superimposed in magnetic tunnel junction: results and inferences. The influence of ballistic channels superimposed on tunneling conduction
channels in magnetic tunnel junctions has been studied in a manganese oxide
based tunneling device. Inversion of magnetoresistance has been observed in
magnetic tunnel junctions with pinhole nanocontacts over a broad temperature
range. The tunnel magnetoresistance undergoes a change of sign at higher bias
and temperature. This phenomenon is attributed to the parallel conduction
channels consisting of spin conserved ballistic transport through the pinhole
contact where the transmission probability is close to unity and spin polarized
tunneling across the insulating spacer with weak transmittivity. The results
seem to resolve a controversy regarding ballistic magnetoresistance in
ferromagnetic nanocontacts and establishes that ballistic magnetoresistance do
exist even if the previous results are attributed to magnetostriction and
magnetostatic force related artifacts.

###Effect of high annealing temperature on giant tunnel magnetoresistance ratio of CoFeB/MgO/CoFeB magnetic tunnel junctions|Jun Hayakawa,Shoji Ikeda,Young Min Lee,Fumihiro Matsukura,Hideo Ohno###

Effect of high annealing temperature on giant tunnel magnetoresistance ratio of CoFeB/MgO/CoFeB magnetic tunnel junctions. We report tunnel magnetoresistance (TMR) ratios as high as 472% at room
temperature and 804% at 5 K in pseudo-spin valve (SV) CoFeB/MgO/CoFeB magnetic
tunnel junctions (MTJs) annealed at 450oC, which is approaching the
theoretically predicted value. By contrast, the TMR ratios for exchange-biased
(EB) SV MTJs with a MnIr antiferromagnetic layer are found to drop when they
are annealed at 450oC. Energy dispersive X-ray analysis shows that annealing at
450oC induces interdiffusion of Mn and Ru atoms into the MgO barrier and
ferromagnetic layers in EB-SV MTJs. Mechanisms behind the different annealing
behavior are discussed.

###Understanding stability diagram of perpendicular magnetic tunnel junctions|Witold Skowroński,Maiej Czapkiewicz,Sławomir Ziętek,Jakub Chęciński,Marek Frankowski,Piotr Rzeszut,Jerzy Wrona###

Understanding stability diagram of perpendicular magnetic tunnel junctions. Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference
layer and a composite free layer (FL) are investigated. Different thicknesses
of the FL were tested to obtain an optimal balance between tunneling
magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After
annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer
reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier
thickness corresponding to the resistance area product RA = 10
Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagrams
measured in pillar-shaped MTJs with 130 nm diameter indicate the competition
between spin transfer torque (STT), voltage controlled magnetic anisotropy
(VCMA) and temperature effects in the switching process. An extended stability
phase diagram model that takes into account all three parameters and the
effective damping measured independently using broadband ferromagnetic
resonance technique enabled the determination of both STT and VCMA coefficients
that are responsible for the FL magnetization switching.

###Theory of magnon-mediated tunnel magneto-Seebeck effect|Benedetta Flebus,Gerrit E. W. Bauer,Rembert A. Duine,Yaroslav Tserkovnyak###

Theory of magnon-mediated tunnel magneto-Seebeck effect. The tunnel magneto-Seebeck effect is the dependence of the thermopower of
magnetic tunnel junctions on the magnetic configuration. It is conventionally
interpreted in terms of a thermoelectric generalization of the tunnel
magnetoresistance. Here, we investigate the heat-driven electron transport in
these junctions associated with electron-magnon scattering, using stochastic
Landau-Lifshitz phenomenology and quantum kinetic theory. Our findings
challenge the widely accepted single-electron picture of the tunneling
thermopower in magnetic junctions.

###Tunneling Anisotropic Magnetoresistance of Helimagnet Tunnel Junctions|Chenglong Jia,Jamal Berakdar###

Tunneling Anisotropic Magnetoresistance of Helimagnet Tunnel Junctions. We theoretically investigate the angular and spin dependent transport in
normal-metal/helical-multiferroic/ferromagnetic heterojunctions. We find a
tunneling anisotropic magnetoresistance (TAMR) effect due to the spiral
magnetic order in the tunnel junction and to an effective spin-orbit coupling
induced by the topology of the localized magnetic moments in the multiferroic
spacer.
  The predicted TAMR effect is efficiently controllable by an external electric
field due to the magnetoelectric coupling.

###GaMnAs-based magnetic tunnel junctions with an AlMnAs barrier|Shinobu Ohya,Iriya Muneta,Pham Nam Hai,Masaaki Tanaka###

GaMnAs-based magnetic tunnel junctions with an AlMnAs barrier. We investigate the spin-dependent transport of GaMnAs-based magnetic tunnel
junctions (MTJs) containing a paramagnetic AlMnAs barrier with various
thicknesses. The barrier height of AlMnAs with respect to the Fermi level of
GaMnAs is estimated to be 110 meV. We observe tunneling magnetoresistance (TMR)
ratios up to 175% (at 2.6 K), which is higher than those of the GaMnAs-based
MTJs with other barrier materials in the same temperature region. These high
TMR ratios can be mainly attributed to the relatively high crystal quality of
AlMnAs and the suppression of the tunneling probability near at the in-plane
wave-vector k||=0.

###Inversion of magnetoresistance in magnetic tunnel junctions : effect of pinhole nanocontacts|Soumik Mukhopadhyay,I. Das###

Inversion of magnetoresistance in magnetic tunnel junctions : effect of pinhole nanocontacts. Inverse magnetoresistance has been observed in magnetic tunnel junctions with
pinhole nanocontacts over a broad temperature range. The tunnel
magnetoresistance undergoes a change of sign at higher bias and temperature.
This phenomenon is attributed to the competition between the spin conserved
ballistic transport through the pinhole contact where the transmission
probability is close to unity and spin polarized tunneling across the
insulating spacer with weak transmittivity.

###Perpendicular magnetic tunnel junctions with multi-interface free layer|Pravin Khanal,Bowei Zhou,Magda Andrade,Yanliu Dang,Albert Davydov,Ali Habiboglu,Jonah Saidian,Adam Laurie,Jian-Ping Wang,Daniel B Gopman,Weigang Wang###

Perpendicular magnetic tunnel junctions with multi-interface free layer. Future generations of magnetic random access memory demand magnetic tunnel
junctions that can provide simultaneously high magnetoresistance, strong
retention, low switching energy and small cell size below 10nm. Here we study
perpendicular magnetic tunnel junctions with composite free layers where
multiple ferromagnet/nonmagnet interfaces can contribute to the thermal
stability. Different nonmagnetic materials (MgO, Ta, Mo) have been employed as
the coupling layers in these multi-interface free layers. The evolution of
junction properties under different annealing conditions is investigated. A
strong dependence of tunneling magnetoresistance on the thickness of the first
CoFeB layer has been observed. In junctions where Mo and MgO are used as
coupling layers, large tunneling magnetoresistance above 200% has been achieved
after 400{\deg}C annealing.

###Crossed-anisotropy films for magnetic tunnel junctions and magnetic memory applications|A. N. Grigorenko,D. J. Mapps###

Crossed-anisotropy films for magnetic tunnel junctions and magnetic memory applications. A prototype of magnetoresistive random access memory (MRAM) based on magnetic
tunnel junctions (MTJ) was fabricated with crossed-anisotropy of magnetic
layers on either side of the tunnelling barrier layer. It is demonstrated that
the introduction of crossed-anisotropy results in smaller switching fields and
better switching times compared to the conventional case of aligned
anisotropies. The magnetoresistive properties of fabricated devices are in good
agreement with the micromagnetic model.

###MgGa2O4 spinel barrier for magnetic tunnel junctions: coherent tunneling and low barrier height|Hiroaki Sukegawa,Yushi Kato,Mohamed Belmoubarik,P. -H. Cheng,Tadaomi Daibou,Naoharu Shimomura,Yuuzo Kamiguchi,Junichi Ito,Hiroaki Yoda,Tadakatsu Ohkubo,Seiji Mitani,Kazuhiro Hono###

MgGa2O4 spinel barrier for magnetic tunnel junctions: coherent tunneling and low barrier height. Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel
junctions (MTJs) were fabricated by magnetron sputtering. Tunnel
magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4 K) was
observed, suggesting a TMR enhancement by the coherent tunneling effect in the
MgGa2O4 barrier. The MgGa2O4 layer had a spinel structure and it showed good
lattice matching with the Fe layers owing to slight tetragonal lattice
distortion of MgGa2O4. Barrier thickness dependence of the tunneling resistance
and current-voltage characteristics revealed that the barrier height of the
MgGa2O4 barrier is much lower than that in an MgAl2O4 barrier. This study
demonstrates the potential of Ga-based spinel oxides for MTJ barriers having a
large TMR ratio at a low resistance area product.

###Current-driven magnetization switching in CoFeB/MgO/CoFeB magnetic tunnel junctions|Jun Hayakawa,Shoji Ikeda,Young Min Lee,Ryutaro Sasaki,Toshiyasu Meguro,Fumihiro Matsukura,Hiromasa Takahashi,Hideo Ohno###

Current-driven magnetization switching in CoFeB/MgO/CoFeB magnetic tunnel junctions. Current-driven magnetization switching in low-resistance
Co40Fe40B20/MgO/Co40Fe40B20 magnetic tunnel junctions (MTJs) is reported. The
critical-current densities Jc required for current-driven switching in samples
annealed at 270C and 300C are found to be as low as 7.8 x 10^5 A/cm^2 and 8.8 x
10^5 A/cm^2 with accompanying tunnel magnetoresistance (TMR) ratios of 49% and
73 %, respectively. Further annealing of the samples at 350C increases TMR
ratio to 160 %, while accompanying Jc increases to 2.5 x 10^6 A/cm^2. We
attribute the low Jc to the high spin-polarization of tunnel current and small
MsV product of the CoFeB single free layer, where Ms is the saturation
magnetization and V the volume of the free layer.

###Electrical detection of a skyrmion in a magnetic tunneling junction|Keita Hamamoto,Naoto Nagaosa###

Electrical detection of a skyrmion in a magnetic tunneling junction. We theoretically investigated a method to detect a single skyrmion in a
magnetic tunneling junction (MTJ) geometry. Using the tunneling Hamiltonian
approach, we calculated the tunneling magnetoresistance (TMR) ratio of the
skyrmion-ferromagnet bilayer system. We show the TMR ratio is determined sorely
by the spin profile of the skyrmion and geometrical factor of the device, if
only the system is reasonably clean such that the spectral broadening is
smaller than the exchange coupling between the local and the itinerant magnetic
moment. The TMR ratio in that case can amount to $30\%$ or higher when the
diameter of the skyrmion is as large as the size of the device. Since this
criterion is easily achievable in real systems, MTJ geometry can be a good
candidate of the electrical detection of a single skyrmion i.e., the reading
process of the information in the future skyrmionics memory devices.

###Spin-transfer torque switching below 20 kA/cm$^2$ in perpendicular magnetic tunnel junctions|Johannes Christian Leutenantsmeyer,Marvin Walter,Steffen Wittrock,Patrick Peretzki,Henning Schuhmann,Michael Seibt,Markus Münzenberg###

Spin-transfer torque switching below 20 kA/cm$^2$ in perpendicular magnetic tunnel junctions. We demonstrate the reduction of critical spin-transfer torque (STT) switching
currents in Co-Fe-B/MgO based magnetic tunnel junctions (MTJ) with
perpendicular magnetization anisotropy (PMA). The junctions yield tunnel
magnetoresistance (TMR) ratios of up to 64% at 4 monolayer (ML) tunnel barrier
thickness. In this paper, the reduction of the critical switching current
density is studied. By optimizing the applied bias field during DC-STT
measurements, ultra low critical switching current densities of less than 20
kA/cm$^2$, even down to 9 kA/cm$^2$, are found. With the reduced switching
currents, our samples are ideal candidates for further experimental studies
such as the theoretical predicted thermally driven spin-transfer torque effect.

###Field-free all-optical switching and electrical read-out of Tb/Co-based magnetic tunnel junctions|D. Salomoni,Y. Peng,L. Farcis,S. Auffret,M. Hehn,G. Malinowski,S. Mangin,B. Dieny,L. D. Buda-Prejbeanu,R. C. Sousa,I. L. Prejbeanu###

Field-free all-optical switching and electrical read-out of Tb/Co-based magnetic tunnel junctions. Switching of magnetic tunnel junction using femto-second laser enables a
possible path for THz frequency memory operation, which means writing speeds 2
orders of magnitude faster than alternative electrical approaches based on spin
transfer or spin orbit torque. In this work we demonstrate successful
field-free 50fs single laser pulse driven magnetization reversal of [Tb/Co]
based storage layer in a perpendicular magnetic tunnel junction. The
nanofabricated magnetic tunnel junction devices have an optimized bottom
reference electrode and show Tunnel Magnetoresistance Ratio values (TMR) up to
74\% after patterning down to sub-100nm lateral dimensions. Experiments on
continuous films reveal peculiar reversal patterns of concentric rings with
opposite magnetic directions, above certain threshold fluence. These rings have
been correlated to patterned device switching probability as a function of the
applied laser fluence. Moreover, the magnetization reversal is independent on
the duration of the laser pulse. According to our macrospin model, the
underlying magnetization reversal mechanism can be attributed to an in-plane
reorientation of the magnetization due to a fast reduction of the out-of-plane
uniaxial anisotropy. These aspects are of great interest both for the physical
understanding of the switching phenomenon and their consequences for
all-optical-switching memory devices, since they allow for a large fluence
operation window with high resilience to pulse length variability.

###Spin effects in single-electron tunneling in magnetic junctions|J. Martinek,J. Barnas,G. Michalek,B. R. Bulka,A. Fert###

Spin effects in single-electron tunneling in magnetic junctions. Spin dependent single electron tunneling in ferromagnetic double junctions is
analysed theoretically in the limit of sequential tunneling. The influence of
discrete energy spectrum of the central electrode (island)on the spin
accumulation, spin fluctuations and tunnel magnetoresistance is analysed
numerically in the case of a nonmagnetic island. It is shown that spin
fluctuations are significant in magnetic as well as in nonmagnetic junctions.

###Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl|Ali Habiboglu,Yash Chandak,Pravin Khanal,Bowei Zhou,Carter Eckel,Jacob Cutshall Kennedy Warrilow,John O'Brien,John R. Schaibley,Brian J. Leroy,Wei-Gang Wang###

Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl. Heusler alloys based magnetic tunnel junctions can potentially provide high
magnetoresistance, small damping and fast switching. Here junctions with
Co2FeAl as a ferromagnetic electrode are fabricated by room temperature
sputtering on Si/SiO2 substrates. The doping of Boron in Co2FeAl is found to
have a large positive impact on the structural, magnetic and transport
properties of the junctions, with a reduced interfacial roughness and
substantial improved tunneling magnetoresistance. A two-level magnetoresistance
is also observed in samples annealed at low temperature, which is believed to
be related to the memristive effect of the tunnel barrier with impurities.

###Measurement of the Spin-Transfer-Torque Vector in Magnetic Tunnel Junctions|J. C. Sankey,Y. -T. Cui,R. A. Buhrman,D. C. Ralph,J. Z. Sun,J. C. Slonczewski###

Measurement of the Spin-Transfer-Torque Vector in Magnetic Tunnel Junctions. Spin-polarized currents can transfer spin angular momentum to a ferromagnet,
generating a torque that can efficiently reorient its magnetization. Achieving
quantitative measurements of the spin-transfer-torque vector in magnetic tunnel
junctions (MTJs) is important for understanding fundamental mechanisms
affecting spin-dependent tunneling, and for developing magnetic memories and
nanoscale microwave oscillators. Here we present direct measurements of both
the magnitude and direction of the spin torque in Co60Fe20B20/MgO/Co60Fe20B20
MTJs. At low bias V, the differential torque vector d{tau}/dV lies in the plane
defined by the electrode magnetizations, and its magnitude is in excellent
agreement with a prediction for highly-spin-polarized tunneling. With
increasing bias, the in-plane component d{tau}_{parallel}/dV remains large, in
striking contrast to the decreasing magnetoresistance ratio. The differential
torque vector also rotates out of the plane under bias; we measure a
perpendicular component tau_{perp}(V) with bias dependence proportional to V^2
for low V, that becomes as large as 30% of the in-plane torque.

###Dependence of Giant Tunnel Magnetoresistance of Sputtered CoFeB/MgO/CoFeB Magnetic Tunnel Junctions on MgO Barrier Thickness and Annealing Temperatur|Jun Hayakawa,Shoji Ikeda,Fumihiro Matsukura,Hiromasa Takahashi,Hideo Ohno###

Dependence of Giant Tunnel Magnetoresistance of Sputtered CoFeB/MgO/CoFeB Magnetic Tunnel Junctions on MgO Barrier Thickness and Annealing Temperatur. We investigated the dependence of giant tunnel magnetoresistance (TMR) on the
thickness of an MgO barrier and on the annealing temperature of sputtered
CoFeB/MgO/CoFeB magnetic tunnel junctions deposited on SiO2/Si wafers. The
resistance-area product exponentially increases with MgO thickness, indicating
that the quality of MgO barriers is high in the investigated thickness range of
1.15-2.4 nm. High-resolution transmission electron microscope images show that
annealing at 375 C results in the formation of crystalline CoFeB/MgO/CoFeB
structures, even though CoFeB electrodes are amorphous in the as-sputtered
state. The TMR ratio increases with annealing temperature and is as high as
260% at room temperature and 403% at 5 K.

###Current induced resistance change of magnetic tunnel junctions with ultra-thin MgO tunnel barriers|Patryk Krzysteczko,Xinli Kou,Karsten Rott,Andy Thomas,Günter Reiss###

Current induced resistance change of magnetic tunnel junctions with ultra-thin MgO tunnel barriers. Ultra-thin magnetic tunnel junctions with low resistive MgO tunnel barriers
are prepared to examine their stability under large current stress. The devices
show magnetoresistance ratios of up to 110 % and an area resistance product of
down to 4.4 ohm micrometer squared. If a large current is applied, a reversible
resistance change is observed, which can be attributed to two different
processes during stressing and one relaxation process afterwards. Here, we
analyze the time dependence of the resistance and use a simple model to explain
the observed behavior. The explanation is further supported by numerical fits
to the data in order to quantify the timescales of the involved phenomena.

###Impurity-limited quantum transport variability in magnetic tunnel junctions|Jianing Zhuang,Yin Wang,Yan Zhou,Jian Wang,Hong Guo###

Impurity-limited quantum transport variability in magnetic tunnel junctions. We report an extensive first-principles investigation of impurity-induced
device-to-device variability of spin-polarized quantum tunneling through
Fe/MgO/Fe magnetic tunnel junctions (MTJ). In particular, we calculated the
tunnel magnetoresistance ratio (TMR) and the average values and variances of
the currents and spin transfer torque (STT) of an interfacially doped Fe/MgO/Fe
MTJ. Further, we predicted that N-doped MgO can improve the performance of a
doped Fe/MgO/Fe MTJ. Our first-principles calculations of the fluctuations of
the on/off currents and STT provide vital information for future predictions of
the long-term reliability of spintronic devices, which is imperative for
high-volume production.

###Planar Hall Effect MRAM|Y. Bason,L. Klein,J. -B. Yau,X. Hong,J. Hoffman,C. H. Ahn###

Planar Hall Effect MRAM. We suggest a new type of magnetic random access memory (MRAM) that is based
on the phenomenon of the planar Hall effect (PHE) in magnetic films, and we
demonstrate this idea with manganite films. The PHE-MRAM is structurally
simpler than currently developed MRAM that is based on magnetoresistance tunnel
junctions (MTJ), with the tunnel junction structure being replaced by a single
layer film.

###Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited $MgAl_{2}O_{4}$/Fe(001) magnetic tunnel junctions|Mohamed Belmoubarik,Hiroaki Sukegawa,Tadakatsu Ohkubo,Seiji Mitani,Kazuhiro Hono###

Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited $MgAl_{2}O_{4}$/Fe(001) magnetic tunnel junctions. We investigated the effect of a Mg-Al layer insertion at the bottom interface
of epitaxial Fe/$MgAl_{2}O_{4}$/Fe(001) magnetic tunnel junctions (MTJs) on
their spin-dependent transport properties. The tunnel magnetoresistance (TMR)
ratio and differential conductance spectra for the parallel magnetic
configuration exhibited clear dependence on the inserted Mg-Al thickness. A
slight Mg-Al insertion (thickness < 0.1 nm) was effective for obtaining a large
TMR ratio above 200% at room temperature and observing a distinct local minimum
structure in conductance spectra. In contrast, thicker Mg-Al (> 0.2 nm) induced
a reduction of TMR ratios and featureless conductance spectra, indicating a
degradation of the bottom-Fe/$MgAl_{2}O_{4}$ interface. Therefore, a minimal
Mg-Al insertion was found to be effective to maximize the TMR ratio for a
sputtered $MgAl_{2}O_{4}$-based MTJ.

###Circuit model for spin-bottleneck resistance in magnetic-tunnel-junction devices|T. Jungwirth,A. H. MacDonald###

Circuit model for spin-bottleneck resistance in magnetic-tunnel-junction devices. Spin-bottlenecks are created in magnetic-tunnel-junction devices by spatial
inhomogeneity in the relative resistances for up and down spins. We propose a
simple electrical circuit model for these devices which incorporates
spin-bottleneck effects and can be used to calculate their overall resistance
and magnetoresistance. The model permits a simple understanding of the
dependence of device magnetoresistance on spin diffusion lengths, tunneling
magnetoresistance, and majority and minority spin resistivities in the
ferromagnetic electrodes. The circuit model is in a good quantitative agreement
with detailed transport calculations.

###Stoner-Wohlfart model applied to bicrystal magnetoresistance hysteresis|R. Gunnarsson,M. Hanson,C. Dubourdieu###

Stoner-Wohlfart model applied to bicrystal magnetoresistance hysteresis. We calculate numerically the magnetization direction as function of magnetic
field in the Stoner-Wohlfart theory and are able to reproduce the shape of the
low-field magnetoresistance hysteresis observed in manganite grain boundary
junctions. Moreover, we show that it is necessary to include biaxial
magnetocrystalline anisotropy to fully describe the grain boundary
magnetoresistance in La$_{0.7}$Sr$_{0.3}$MnO$_3$/SrTiO$_3$ bicrystal tunnel
junctions.

###L10 Fe-Pd Synthetic Antiferromagnet through an fcc Ru Spacer Utilized for Perpendicular Magnetic Tunnel Junctions|De-Lin Zhang,Congli Sun,Yang Lv,Karl B. Schliep,Zhengyang Zhao,Jun-Yang Chen,Paul M. Voyles,Jian-Ping Wang###

L10 Fe-Pd Synthetic Antiferromagnet through an fcc Ru Spacer Utilized for Perpendicular Magnetic Tunnel Junctions. Magnetic materials that possess large bulk perpendicular magnetic anisotropy
(PMA) are essential for the development of magnetic tunnel junctions (MTJs)
used in future spintronic memory and logic devices. The addition of an
antiferromagnetic layer to these MTJs was recently predicted to facilitate
ultra-fast magnetization switching. Here, we report a demonstration of a bulk
perpendicular synthetic antiferromagnetic (P-SAFM) structure comprised of a
(001) textured FePd/Ru/FePd trilayer with a face-centered-cubic (fcc) phase Ru
spacer. The L10 FePd P-SAFM structure shows a large bulk PMA (~10.2 Merg/cc)
and strong antiferromagnetic coupling (~2.60 erg/cm2). Full perpendicular
magnetic tunnel junctions (P-MTJs) with a L10 FePd P-SAFM layer are then
fabricated. Tunneling magnetoresistance ratios of up to ~25% (~60%) are
observed at room temperature (5K) after post-annealing at 350 C. Exhibiting
high thermal stabilities and large Ku, the bulk P-MTJs with an L10 FePd P-SAFM
layer could pave a way for next-generation ultrahigh-density and
ultra-low-energy spintronic applications.

###Spin-dependent resonant tunneling through quantum-well states in magnetic metallic thin films|Zhong-Yi Lu,X. -G. Zhang,Sokrates T. Pantelides###

Spin-dependent resonant tunneling through quantum-well states in magnetic metallic thin films. Quantum-well (QW) states in {\it nonmagnetic} metal layers contained in
magnetic multilayers are known to be important in spin-dependent transport, but
the role of QW states in {\it magnetic} layers remains elusive. Here we
identify the conditions and mechanisms for resonant tunneling through QW states
in magnetic layers and determine candidate structures. We report
first-principles calculations of spin-dependent transport in epitaxial
Fe/MgO/FeO/Fe/Cr and Co/MgO/Fe/Cr tunnel junctions. We demonstrate the
formation of sharp QW states in the Fe layer and show discrete conductance
jumps as the QW states enter the transport window with increasing bias. At
resonance, the current increases by one to two orders of magnitude. The
tunneling magnetoresistance ratio is several times larger than in simple spin
tunnel junctions and is positive (negative) for majority- (minority-) spin
resonances, with a large asymmetry between positive and negative biases. The
results can serve as the basis for novel spintronic devices.

###Spin Transfer Switching and Spin Polarization in Magnetic Tunnel Junctions with Mgo and Alox Barriers|Zhitao Diao,Dmytro Apalkov,Mahendra Pakala,Alex Panchula,Yiming Huai###

Spin Transfer Switching and Spin Polarization in Magnetic Tunnel Junctions with Mgo and Alox Barriers. We present spin transfer switching results for MgO based magnetic tunneling
junctions (MTJs)with large tunneling magnetoresistance (TMR) ratio of up to
150% and low intrinsic switching current density of 2-3 x 10 MA/cm2. The
switching data are compared to those obtained on similar MTJ nanostructures
with AlOx barrier. It is observed that the switching current density for MgO
based MTJs is 3-4 times smaller than that for AlOx based MTJs, and that can be
attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In
addition, we report a qualitative study of TSP for a set of samples, ranging
from 0.22 for AlOx to 0.46 for MgO based MTJs, and that shows the TSP (at
finite bias) responsible for the current-driven magnetization switching is
suppressed as compared to zero-bias tunneling spin polarization determined from
TMR.

###Enhanced Tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) Magnetic Tunnel Junctions|Thomas Scheike,Zhenchao Wen,Hiroaki Sukegawa,Seiji Mitani###

Enhanced Tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) Magnetic Tunnel Junctions. Spinel MgAl2O4 and family oxides are emerging barrier materials useful for
magnetic tunnel junctions (MTJs). We report large tunnel magnetoresistance
(TMR) ratios up to 429% at room temperature (RT) and 1,034% at 10 K in a
Fe/MgAl2O4/Fe(001)-based MTJ prepared using electron-beam evaporation of
Mg4Al-Ox. Resistance oscillations with a MTJ barrier thickness of 0.3-nm were
significantly enhanced compared to those of a Fe/MgO/Fe(001) MTJ, resulting in
a large TMR oscillation peak-to-valley difference of 125% at RT. The
differential conductance spectra were symmetric with bias polarity, and the
spectrum in the parallel magnetization state at low temperature demonstrate
significant peaks within broad local minima at |0.2-0.6| V, indicating improved
barrier interfaces by the Mg4Al-Ox barrier. This study demonstrates that TMR
ratios in Fe(001)-MTJs can still be improved.

###Supramolecular Spin Valves|Matias Urdampilleta,Svetlana Klyatskaya,Jean-Pierre Cleuziou,Mario Ruben,Wolfgang Wernsdorfer###

Supramolecular Spin Valves. Magnetic molecules possess a high potential as building blocks for the design
of spintronic devices. Moreover, the use of molecular materials opens the way
for the controlled use of bottom-up, e.g. supramolecular, processing techniques
combining massively parallel self-fabrication with conventional top-down
nanostructuring techniques. The development of solid state spintronic devices
based on the giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), and
spin valve effects has revolutionized the field of magnetic memory
applications. Recently, organic semiconductors were inserted into nanometer
sized tunnel junctions allowing enhancement of spin reversal, giant
magneto-resistance behaviour was observed in single non-magnetic molecules
coupled to magnetic electrodes, and the use of the quantum tunnelling
properties of single-molecule magnets (SMMs) in hybrid devices was proposed.
Herein, we present an original device in which a non-magnetic molecular quantum
dot, made of a single-wall carbon nanotube (SWCNT) contacted with non-magnetic
electrodes, is laterally coupled via supramolecular interactions to a TbPc2-SMM
(Pc = phthalocyanine), which provides a localized magnetic moment. The
conductance through the SWCNT is modulated by sweeping the magnetic field,
exhibiting magnetoresistance ratios up to 300% between fully polarized and
non-polarized SMMs below 1 K. We thus demonstrate the functionality of a
supramolecular spin valve without magnetic leads. Our results open up prospects
of circuit-integration and implementation of new device capabilities.

###Colossal Magnetoresistance Manganites and Related Prototype Devices|Yukuai Liu,Yuewei Yin,Xiaoguang Li###

Colossal Magnetoresistance Manganites and Related Prototype Devices. We review colossal magnetoresistance in single phase manganites, as related
to the field sensitive spin charge interactions and phase separation; the
rectifying property and negative/positive magnetoresistance in
manganite/Nb:SrTiO3 pn junctions in relation to the special interface
electronic structure; magnetoelectric coupling in manganite/ferroelectric
structures that takes advantage of strain, carrier density, and magnetic field
sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric,
ferroelectric, and organic semiconductor spacers using the fully spin polarized
nature of manganites; and the effect of particle size on magnetic properties in
manganite nanoparticles

###Spin-Dependent Coulomb Blockade in Ferromagnet/Normal-Metal/Ferromagnet Double Tunnel Junctions|Hiroshi Imamura,Saburo Takahashi,Sadamichi Maekawa###

Spin-Dependent Coulomb Blockade in Ferromagnet/Normal-Metal/Ferromagnet Double Tunnel Junctions. We study theoretically the spin-dependent transport in
ferromagnet/normal-metal/ferromagnet double tunnel junctions by special
attention to cotunneling in the Coulomb blockade region. The spin accumulation
caused by cotunneling squeezes the Coulomb blockade region when the
magnetizations in the ferromagnetic electrodes are antiparallel. Outside the
squeezed Coulomb blockade region, we propose a new anomalous region, where the
sequential tunneling in one of the spin bands is suppressed by the Coulomb
blockade and that in the other is not. In this region, the tunnel
magnetoresistance oscillates as a function of bias voltage. The temperature
dependences of the tunnel magnetoresistance and the magnitude of the spin
accumulation are calculated.

###Interplay of symmetry-conserved tunneling, interfacial oxidation and perpendicular magnetic anisotropy in CoFeB/MgO-based junctions|Pravin Khanal,Bowei Zhou,Hamid Almasi,Ali Habiboglu,Magda Andrade,Jack O'Brien,Arthur Enriquez,Carter Eckel,Christopher Mastrangelo,Wei-Gang Wang###

Interplay of symmetry-conserved tunneling, interfacial oxidation and perpendicular magnetic anisotropy in CoFeB/MgO-based junctions. The interfacial oxidation level and thermodynamic properties of the MgO-based
perpendicular magnetic tunneling junctions are investigated. The
symmetry-conserved tunneling effect depends sensitively on the MgO adatom
energy during the RF sputtering, as well as the thermal stability of the
structure during the post-growth thermal annealing. Two different failure modes
of the magnetoresistance are highlighted, involving with the decay of
perpendicular magnetic anisotropy and destruction of coherent tunneling
channels, respectively. Through the careful control of interfacial oxidation
level and proper selection of the heavy metal layers, both perpendicular
magnetic anisotropy and tunneling magnetoresistance of the junctions can be
increased.

###Spin flip scattering in magnetic junctions|F. Guinea###

Spin flip scattering in magnetic junctions. Processes which flip the spin of an electron tunneling in a junction made up
of magnetic electrodes are studied. It is found that: i) Magnetic impurities
give a contribution which increases the resistance and lowers the
magnetoresistance, which saturates at low temperatures. The conductance
increases at high fields. ii) Magnon assisted tunneling reduces the
magnetoresistance as $T^{3/2}$, and leads to a non ohmic contribution to the
resistance which goes as $V^{3/2}$, iii) Surface antiferromagnetic magnons,
which may appear if the interface has different magnetic properties from the
bulk, gives rise to $T^2$ and $V^2$ contributions to the magnetoresistance and
resistance, respectively, and, iv) Coulomb blockade effects may enhance the
magnetoresistance, when transport is dominated by cotunneling processes.

###Strain-programmable van der Waals magnetic tunnel junctions|John Cenker,Dmitry Ovchinnikov,Harvey Yang,Daniel G. Chica,Catherine Zhu,Jiaqi Cai,Geoffrey Diederich,Zhaoyu Liu,Xiaoyang Zhu,Xavier Roy,Ting Cao,Matthew W. Daniels,Jiun-Haw Chu,Di Xiao,Xiaodong Xu###

Strain-programmable van der Waals magnetic tunnel junctions. The magnetic tunnel junction (MTJ) is a backbone device for spintronics.
Realizing next generation energy efficient MTJs will require operating
mechanisms beyond the standard means of applying magnetic fields or large
electrical currents. Here, we demonstrate a new concept for programmable MTJ
operation via strain control of the magnetic states of CrSBr, a layered
antiferromagnetic semiconductor used as the tunnel barrier. Switching the CrSBr
from antiferromagnetic to ferromagnetic order generates a giant tunneling
magnetoresistance ratio without external magnetic field at temperatures up to ~
140 K. When the static strain is set near the phase transition, applying small
strain pulses leads to active flipping of layer magnetization with controlled
layer number and thus magnetoresistance states. Further, finely adjusting the
static strain to a critical value turns on stochastic switching between
metastable states, with a strain-tunable sigmoidal response curve akin to the
stochastic binary neuron. Our results highlight the potential of
strain-programmable van der Waals MTJs towards spintronic applications, such as
magnetic memory, random number generation, and probabilistic and neuromorphic
computing.

###Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions|Li Ming Loong,Xuepeng Qiu,Zhi Peng Neo,Praveen Deorani,Yang Wu,Charanjit S. Bhatia,Mark Saeys,Hyunsoo Yang###

Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions. While the effects of lattice mismatch-induced strain, mechanical strain, as
well as the intrinsic strain of thin films are sometimes detrimental, resulting
in mechanical deformation and failure, strain can also be usefully harnessed
for applications such as data storage, transistors, solar cells, and strain
gauges, among other things. Here, we demonstrate that quantum transport across
magnetic tunnel junctions (MTJs) can be significantly affected by the
introduction of controllable mechanical strain, achieving an enhancement factor
of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further
correlate this strain-enhanced TMR with coherent spin tunneling through the MgO
barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium
Green's function (NEGF) quantum transport calculations. Our results help
elucidate the TMR mechanism at the atomic level and can provide a new way to
enhance, as well as tune, the quantum properties in nanoscale materials and
devices.

###Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide|Miho Arai,Rai Moriya,Naoto Yabuki,Satoru Masubuchi,Keiji Ueno,Tomoki Machida###

Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide. We investigate the micromechanical exfoliation and van der Waals (vdW)
assembly of ferromagnetic layered dichalcogenide Fe0.25TaS2. The vdW interlayer
coupling at the Fe-intercalated plane of Fe0.25TaS2 allows exfoliation of
flakes. A vdW junction between the cleaved crystal surfaces is constructed by
dry transfer method. We observe tunnel magnetoresistance in the resulting
junction under an external magnetic field applied perpendicular to the plane,
demonstrating spin-polarized tunneling between the ferromagnetic layered
material through the vdW junction.

###Spin- and Symmetry-Filtering Combined Tunnel Magnetoresistance through Epitaxial MgO/EuS Tunnel Barriers|Zhiwei Gao,Yihang Yang,Fen Liu,Qian Xue,Guo-Xing Miao###

Spin- and Symmetry-Filtering Combined Tunnel Magnetoresistance through Epitaxial MgO/EuS Tunnel Barriers. We created epitaxial magnetic tunnel junctions of FeCo/MgO/EuS on MgO
buffered Si (100). Tunnel magnetoresistance reached up to 64% at 4.2 K. An
unexpected fast drop of magnetoresistance was recorded for MgO thickness above
1 nm, which is attributed to the forced nonspecular conductance across the EuS
conduction band minimum located at the X point, rather than the desired Delta_1
conductance centered around the Gamma point.

###Magnetic tunneling junctions with the Heusler compound Co_2Cr_{0.6}Fe_{0.4}Al|A. Conca,S. Falk,G. Jakob,M. Jourdan,H. Adrian###

Magnetic tunneling junctions with the Heusler compound Co_2Cr_{0.6}Fe_{0.4}Al. The Heusler alloy is used as an electrode of magnetic tunneling junctions.
The junctions are deposited by magnetron dc sputtering using shadow mask
techniques with AlO_{x} as a barrier and cobalt as counter electrode.
Measurements of the magnetoresistive differential conductivity in a temperature
range between 4K and 300K are shown. An analysis of the barrier properties
applying the Simmons model to the bias dependent junction conductivity is
performed. VSM measurements were carried out to examine the magnetic properties
of the samples.

###MgO barrier-perpendicular magnetic tunnel junctions with CoFe/Pd multilayers and ferromagnetic insertion layers|K. Mizunuma,S. Ikeda,J. H. Park,H. Yamamoto,H. Gan,K. Miura,H. Hasegawa,J. Hayakawa,F. Matsukura,H. Ohno###

MgO barrier-perpendicular magnetic tunnel junctions with CoFe/Pd multilayers and ferromagnetic insertion layers. The authors studied an effect of ferromagnetic (Co20Fe60B20 or Fe) layer
insertion on tunnel magnetoresistance (TMR) properties of MgO-barrier magnetic
tunnel junctions (MTJs) with CoFe/Pd multilayer electrodes. TMR ratio in MTJs
with CoFeB/MgO/Fe stack reached 67% at an-nealing temperature (Ta) of 200
degree C and then decreased rapidly at Ta over 250 degree C. The degradation of
the TMR ratio may be related to crystallization of CoFe(B) into fcc(111) or
bcc(011) texture result-ing from diffusion of B into Pd layers. MTJs which were
in-situ annealed at 350oC just after depo-siting bottom CoFe/Pd multilayer
showed TMR ratio of 78% by post annealing at Ta =200 degree C.

###Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy|Tomoki Tsuchiya,Tufan Roy,Kelvin Elphick,Jun Okabayashi,Lakhan Bainsla,Tomohiro Ichinose,Kazuya Suzuki,Masahito Tsujikawa,Masafumi Shirai,Atsufumi Hirohata,Shigemi Mizukami###

Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy. The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for
spin-gapless semiconductors (SGSs). However, to date, there have been no
experimental attempts at fabricating a junction device. This paper reports a
fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with
CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction
measurements show that the (001) CoFeCrAl electrode films with atomically flat
surfaces have a $B2$-ordered phase. The saturation magnetization is 380
emu/cm$^3$, almost the same as the value given by the Slater--Pauling--like
rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87%
and 165%, respectively. Cross-sectional electron diffraction analysis shows
that the MTJs have MgO interfaces with fewer dislocations. The temperature- and
bias-voltage-dependence of the transport measurements indicates magnon-induced
inelastic electron tunneling overlapping with the coherent electron tunneling.
X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic
arrangement of the Co and Fe magnetic moments of $B2$-ordered CoFeCrAl, in
contrast to the ferrimagnetic arrangement predicted for the $Y$-ordered state
possessing SGS characteristics. Ab-initio calculations taking account of the
Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect
of the Cr-Fe swap disorder on the ability for electronic states to allow
coherent electron tunneling is discussed.

###On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect|Alexander Boehnke,Marius Milnikel,Marvin Walter,Vladyslav Zbarsky,Christian Franz,Michael Czerner,Karsten Rott,Andy Thomas,Christian Heiliger,Markus Münzenberg,Günter Reiss###

On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect. Thermoelectric effects in magnetic tunnel junctions are currently an
attractive research topic. Here, we demonstrate that the tunnel magneto-Seebeck
effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic
1 state and off to 0 by simply changing the magnetic state of the CoFeB
electrodes. We enable this new functionality of magnetic tunnel junctions by
combining a thermal gradient and an electric field. This new technique unveils
the bias-enhanced tunnel magneto-Seebeck effect, which can serve as the basis
for logic devices or memories in a green information technology with a pure
thermal write and read process. Furthermore, the thermally generated voltages
that are referred to as the Seebeck effect are well known to sensitively depend
on the electronic structure and therefore have been valued in solid-state
physics for nearly one hundred years. Here, we lift Seebeck's historic
discovery from 1821 to a new level of current spintronics. Our results show
that the signal crosses zero and can be adjusted by tuning a bias voltage that
is applied between the electrodes of the junction; hence, the name of the
effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and
energy-dependent transmission of electrons in the junction, the bTMS effect can
be configured using the bias voltage with much higher control than the tunnel
magnetoresistance (TMR) and even completely suppressed for only one magnetic
configuration, which is either parallel (P) or anti-parallel (AP). This option
allows a readout contrast for the magnetic information of -3000% at room
temperature while maintaining a large signal for one magnetic orientation. This
contrast is much larger than the value that can be obtained using the TMR
effect. Moreover, our measurements are a step towards the experimental
realization of high TMS ratios, which are predicted for specific Co-Fe
compositions.

###Spin-dependent tunneling through high-k LaAlO3|V. Garcia,M. Bibes,J. -L. Maurice,E. Jacquet,K. Bouzehouane,J. -P. Contour,A. Barthelemy###

Spin-dependent tunneling through high-k LaAlO3. We report on the use of the LaAlO3 (LAO) high-k dielectric as a tunnel
barrier in magnetic tunnel junctions. From tunnel magnetoresistance (TMR)
measurements on epitaxial La2/3Sr1/3MnO3/LAO/La2/3Sr1/3MnO3 junctions, we
estimate a spin polarization of 77% at low temperature for the
La2/3Sr1/3MnO3/LAO interface. Remarkably, the TMR of La2/3Sr1/3MnO3/LAO/Co
junctions at low bias is negative, evidencing a negative spin polarization of
Co at the interface with LAO, and its bias dependence is very similar to that
of La2/3Sr1/3MnO3/STO/Co junctions. We discuss possible reasons for this
behaviour.

###Tunneling magnetoresistance of Fe/ZnSe (001) single- and double-barrier junctions as a function of interface structure|J. Peralta-Ramos,A. M. Llois###

Tunneling magnetoresistance of Fe/ZnSe (001) single- and double-barrier junctions as a function of interface structure. In this contribution, we calculate the spin-dependent ballistic and coherent
transport through epitaxial Fe/ZnSe (001) simple and double magnetic tunnel
junctions with two different interface terminations: Zn-terminated and
Se-terminated. The electronic structure of the junctions is modeled by a
second-nearest neighbors {\it spd} tight-binding Hamiltonian parametrized to
{\it ab initio} calculated band structures, while the conductances and the
tunneling magnetoresistance are calculated within Landauer's formalism. The
calculations are done at zero bias voltage and as a function of energy. We show
and discuss the influence of the interface structure on the spin-dependent
transport through simple and double tunnel junctions.

###Band-folding-driven high tunnel magnetoresistance ratios in (111)-oriented junctions with SrTiO$_3$ barriers|Keisuke Masuda,Hiroyoshi Itoh,Yoshiaki Sonobe,Hiroaki Sukegawa,Seiji Mitani,Yoshio Miura###

Band-folding-driven high tunnel magnetoresistance ratios in (111)-oriented junctions with SrTiO$_3$ barriers. We theoretically study the tunnel magnetoresistance (TMR) effect in
(111)-oriented magnetic tunnel junctions (MTJs) with SrTiO$_{3}$ barriers,
Co/SrTiO$_{3}$/Co(111) and Ni/SrTiO$_{3}$/Ni(111). Our analysis combining the
first-principles calculation and the Landauer formula shows that the Co-based
MTJ has a high TMR ratio over 500%, while the Ni-based MTJ has a smaller value
(290%). Since the in-plane lattice periodicity of SrTiO$_{3}$ is about twice
that of the primitive cell of fcc Co (Ni), the original bands of Co (Ni) are
folded in the $k_x$-$k_y$ plane corresponding to the $ab$ plane of the MTJ
supercell. We find that this band folding gives a half-metallic band structure
in the $\Lambda_1$ state of Co (Ni) and the coherent tunneling of such a
half-metallic $\Lambda_1$ state yields a high TMR ratio. We also reveal that
the difference in the TMR ratio between the Co- and Ni-based MTJs can be
understood by different $s$-orbital weights in the $\Lambda_1$ band at the
Fermi level.

###Parallel-leaky capacitance equivalent circuit model for MgO magnetic tunnel junctions|Ajeesh M. Sahadevan,Kalon Gopinadhan,Charanjit S. Bhatia,Hyunsoo Yang###

Parallel-leaky capacitance equivalent circuit model for MgO magnetic tunnel junctions. The capacitance of MgO based magnetic tunnel junctions (MTJs) has been
observed to be magnetic field dependent. We propose an equivalent circuit for
the MTJs with a parallel-leaky capacitance (Cl) across the series combination
of geometric and interfacial capacitance. The analysis of junctions with
different tunneling magnetoresistance values suggests higher Cl for low TMR
junctions. Using Cole-Cole plots the capacitive nature of MTJs is manifested.
Fitting with Maxwell-Wagner capacitance model validates the RC parallel network
model for MTJs and the extracted field dependent parameters match with the
experimental values.

###Tunneling Magnetoresistance and Spin-Dependent Diode Performance in Fully Epitaxial Magnetic Tunnel Junctions with Rock-salt Type ZnO/MgO|Hidekazu Saito,Sai Krishna Narayananellore,Norihiro Matsuo,Naoki Doko,Shintaro Kon,Yukiko Yasukawa,Hiroshi Imamura,Shinji Yuasa###

Tunneling Magnetoresistance and Spin-Dependent Diode Performance in Fully Epitaxial Magnetic Tunnel Junctions with Rock-salt Type ZnO/MgO. We fabricate fully epitaxial Fe/ZnO/MgO/Fe magnetic tunnel junctions (MTJs)
with a bilayer tunnel barrier, in which ZnO has a metastable rock-salt crystal
structure. We observe a high magnetoresistance ratio up to 96% at room
temperature (RT) and find that these MTJs have asymmetric current-voltage
characteristics, and their rectifying performances are largely dependent on the
magnetization alignments of the Fe electrodes. Diode responsibilities at a
zero-bias voltage ($\beta_{0}$), which is an important performance index for
harvesting applications, are observed up to 1.3 A/W at RT in the antiparallel
alignment of the magnetizations while maintaining rather low resistance-area
(RA) products (a few tens of k${\Omega\mu}$m$^2$). Even with the same top and
bottom electrodes (Fe), the obtained $\beta_{0}$ values are comparable to those
of reported high-performance tunnel diodes consisting of amorphous bilayer
tunnel barriers with polycrystalline dissimilar electrodes. This strongly
suggests that the epitaxial ZnO/MgO bilayer tunnel barrier is effective for
enhancing the $\beta_{0}$ without significant increase in the RA. In addition,
we demonstrate that a zero-bias anomaly in thetunnel conductance, which
originates from the magnon excitations at the Fe/barrier interfaces, plays a
crucial role in observed spin-dependent diode performance. The results indicate
that a fully epitaxial MTJ with a bilayer tunnel barrier is a promising
candidate to establish a high-performance high-frequency rectifying system.

###Second order anisotropy contribution in perpendicular magnetic tunnel junctions|A. A. Timopheev,R. Sousa,M. Chshiev,T. Nguyen,B. Dieny###

Second order anisotropy contribution in perpendicular magnetic tunnel junctions. Magnetoresistance loops under in-plane applied field were measured on
perpendicularly magnetized magnetic tunnel junction (pMTJ) pillars with nominal
diameters ranging from 50 to 150 nm. By fitting the hard-axis magnetoresistance
loops to an analytical model, the effective anisotropy fields in both free and
reference layers were derived and their variations in temperature range between
340K and 5K were determined. It is found that an accurate fitting is possible
only if a second-order anisotropy term of the form $-K_{2}cos^4{\theta}$, is
added to the fitting model. This higher order contribution exists both in the
free and reference layers and its sign is opposite to that of the first order
anisotropy constant, $K_{1}$. At room temperatures the estimated $-K_{2}/K_{1}$
ratios are 0.1 and 0.24 for the free and reference layers, respectively. The
ratio is more than doubled at low temperatures altering the ground state of the
reference layer from 'easy-axis' to 'easy-cone' regime. Easy-cone state has
clear signatures in the shape of the hard-axis magnetoresistance loops. The
same behavior was observed in all measured devices regardless of their
diameter. The existence of this higher order anisotropy was confirmed
experimentally on FeCoB/MgO sheet films by ferromagnetic resonance technique.
It is of interfacial nature and is believed to be linked to spatial
fluctuations at the nanoscale of the anisotropy parameter at the FeCoB/MgO
interface, in agreement with Dieny-Vedyayev model.

###Spin filtering in CrI$_3$ tunnel junctions|Tula R. Paudel,Evgeny Y. Tsymbal###

Spin filtering in CrI$_3$ tunnel junctions. The recently discovered magnetism of two-dimensional (2D) van der Waals
crystals have attracted a lot of attention. Among these materials is CrI$_3$ -
a magnetic semiconductor exhibiting transitions between antiferromagnetic and
ferromagnetic orderings under the influence of an applied magnetic field. Here,
using first-principles methods based on density functional theory, we explore
spin-dependent transport in tunnel junctions formed of fcc Cu (111) electrodes
and a CrI$_3$ tunnel barrier. We find about 100% spin polarization of the
tunneling current for a ferromagnetically-ordered four-monolayer CrI$_3$ and
tunneling magnetoresistance of about 3,000% associated with a change of
magnetic ordering in CrI$_3$. This behavior is understood in terms of the spin
and wave-vector dependent evanescent states in CrI$_3$ which control the
tunneling conductance. We find a sizable charge transfer from Cu to CrI$_3$
which adds new features to the mechanism of spin-filtering in CrI$_3$-based
tunnel junctions. Our results elucidate the mechanisms of spin filtering in
CrI3 tunnel junctions and provide important insights for the design of
magnetoresistive devices based on 2D magnetic crystals.

###Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers|A. V. Ramos,M. -J. Guittet,J. -B. Moussy,R. Mattana,C. Deranlot,F. Petroff,C. Gatel###

Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers. We report direct experimental evidence of room temperature spin filtering in
magnetic tunnel junctions (MTJs) containing CoFe2O4 tunnel barriers via
tunneling magnetoresistance (TMR) measurements.
Pt(111)/CoFe2O4(111)/gamma-Al2O3(111)/Co(0001) fully epitaxial MTJs were grown
in order to obtain a high quality system, capable of functioning at room
temperature. Spin polarized transport measurements reveal significant TMR
values of -18% at 2 K and -3% at 290 K. In addition, the TMR ratio follows a
unique bias voltage dependence that has been theoretically predicted to be the
signature of spin filtering in MTJs containing magnetic barriers. CoFe2O4
tunnel barriers therefore provide a model system to investigate spin filtering
in a wide range of temperatures.

###Spin-Transfer Effects in Nanoscale Magnetic Tunnel Junctions|G. D. Fuchs,N. C. Emley,I. N. Krivorotov,P. M. Braganca,E. M. Ryan,S. I. Kiselev,J. C. Sankey,J. A. Katine,D. C. Ralph,R. A. Buhrman###

Spin-Transfer Effects in Nanoscale Magnetic Tunnel Junctions. We report measurements of magnetic switching and steady-state magnetic
precession driven by spin-polarized currents in nanoscale magnetic tunnel
junctions with low-resistance, < 5 Ohm-micron-squared, barriers. The current
densities required for magnetic switching are similar to values for
all-metallic spin-valve devices. In the tunnel junctions, spin-transfer-driven
switching can occur at voltages that are high enough to quench the tunnel
magnetoresistance, demonstrating that the current remains spin-polarized at
these voltages.

###Exceeding 400% tunnel magnetoresistance at room temperature in epitaxial Fe/MgO/Fe(001) spin-valve-type magnetic tunnel junctions|Thomas Scheike,Qingyi Xiang,Zhenchao Wen,Hiroaki Sukegawa,Tadakatsu Ohkubo,Kazuhiro Hono,Seiji Mitani###

Exceeding 400% tunnel magnetoresistance at room temperature in epitaxial Fe/MgO/Fe(001) spin-valve-type magnetic tunnel junctions. Giant tunnel magnetoresistance (TMR) ratios of 417% at room temperature (RT)
and 914% at 3 K were demonstrated in epitaxial Fe/MgO/Fe(001) exchanged-biased
spin-valve magnetic tunnel junctions (MTJs) by tuning growth conditions for
each layer, combining sputter deposition for the Fe layers, electron-beam
evaporation of the MgO barrier, and barrier interface tuning. Clear TMR
oscillation as a function of the MgO thickness with a large peak-to-valley
difference of ~80% was observed when the layers were grown on a highly
(001)-oriented Cr buffer layer. Specific features of the observed MTJs are
symmetric differential conductance (dI/dV) spectra for the bias polarity and
plateau-like deep local minima in dI/dV (parallel configuration) at |V| =
0.2~0.5 V. At 3K, fine structures with two dips emerge in the plateau-like
dI/dV, reflecting highly coherent tunneling through the Fe/MgO/Fe. We also
observed a 496% TMR ratio at RT by a 2.24-nm-thick-CoFe insertion at the
bottom-Fe/MgO interface.

###High tunnel magnetoresistance and magnetism in metastable bcc Co$_{1-x}$Mn$_x$-based magnetic tunnel junctions|Kazuma Kunimatsu,Tufan Roy,Jun Okabayashi,Kelvin Elphick,Tomoki Tsuchiya,Tomohiro Ichinose,Masahito Tsujikawa,Atsufumi Hirohata,Masafumi Shirai,Shigemi Mizukami###

High tunnel magnetoresistance and magnetism in metastable bcc Co$_{1-x}$Mn$_x$-based magnetic tunnel junctions. Co-rich Co$_{1-x}$Mn$_x$ alloys have hcp or fcc disordered phases and those
ferromagnetic orderings are significantly deteriorated with increasing Mn
concentration $x$ in bulk. On the other hand, those metastable bcc phases show
properties attractive to spintronics, e.g., high tunnel magnetoresistance (TMR)
ratio of more than 200% (600%) at 300 K (10 K) in magnetic tunnel junctions
(MTJs) with the $x$ = 0.25 bcc alloy electrodes [Kunimatsu et al., Appl. Phys.
Express 13, 083007 (2020)]. Here, we report systematic study of structure and
magnetism for epitaxial thin films as well as the TMR effect in
MgO(001)-barrier MTJs with electrodes comprising those bcc films. The single
phase bcc Co$_{1-x}$Mn$_x$(001) films were pseudomorphically grown on Cr(001)
for 0.14 < $x$ < 0.50 with a sputtering technique. The magnetization was larger
than that of pure Co for $x$ = 0.14-0.25 and deceased with further increasing
$x$. This behavior mainly stemmed from the composition dependence of magnetic
moment of Mn that exceeded 2 $\mu _B$ at the maximum, unveiled by X-ray
magnetic circular dichroism. Correspondingly, within the range of 0.25 < $x$ <
0.37, the TMR ratio decreased from 620% (229%) to 450% (194%) at 10 K (300 K)
as $x$ increased. We discussed the relationship between the magnetism and high
TMR ratio with different $x$ with the aid of the ab-initio band structure
calculations.

###High Bias Voltage Effect on Spin-Dependent Conductivity and Shot Noise in Carbon-doped Fe(001)/MgO(001)/Fe(001) Magnetic Tunnel Junctions|R. Guerrero,D. Herranz,F. G. Aliev,F. Greullet,C. Tiusan,M. Hehn,F. Montaigne###

High Bias Voltage Effect on Spin-Dependent Conductivity and Shot Noise in Carbon-doped Fe(001)/MgO(001)/Fe(001) Magnetic Tunnel Junctions. Low temperature (10K) high voltage bias dynamic conductivity (up to 2.7V) and
shot noise (up to 1V) were studied in epitaxial Fe(100)/Fe-C/MgO(100)/Fe(100)
magnetic tunnel junctions, as a function of the magnetic state. The junctions
show large tunnel magnetoresistance (185% at 300K and 330% at 4K). Multiple
sign inversion of the magnetoresistance is observed for bias polarity when the
electrons scan the electronic structure of the bottom Fe-C interface. The
shot-noise shows a Poissonian character. This demonstrates a pure spin
dependent direct tunneling mechanism and validates the high structural quality
of the MgO barrier.

###Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions|K. Watanabe,B. Jinnai,S. Fukami,H. Sato,H. Ohno###

Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions. Nanoscale magnetic tunnel junction plays a pivotal role in magnetoresistive
random access memories. Successful implementation depends on a simultaneous
achievement of low switching current for the magnetization switching by
spin-transfer torque and high thermal stability, along with a continuous
reduction of junction size. Perpendicular-easy-axis CoFeB/MgO stacks possessing
interfacial anisotropy have paved the way down to 20-nm scale, below which a
new approach needs to be explored. Here we show magnetic tunnel junctions that
satisfy the requirements at ultrafine scale by revisiting shape anisotropy,
which is a classical part of magnetic anisotropy but has not been fully
utilized in the current perpendicular systems. Magnetization switching solely
driven by current is achieved for junctions smaller than 10 nm where sufficient
thermal stability is provided by shape anisotropy without adopting new material
systems. This work is expected to push forward the development of magnetic
tunnel junctions towards single-digit-nm-scale nano-magnetics/spintronics.

###Crossover from Kondo assisted suppression to co-tunneling enhancement of tunneling magnetoresistance via ferromagnetic nanodots in MgO tunnel barriers|Hyunsoo Yang,See-Hun Yang,Stuart Parkin###

Crossover from Kondo assisted suppression to co-tunneling enhancement of tunneling magnetoresistance via ferromagnetic nanodots in MgO tunnel barriers. Recently, it has been shown that magnetic tunnel junctions with thin MgO
tunnel barriers exhibit extraordinarily high tunneling magnetoresistance (TMR)
values at room temperature1, 2. However, the physics of spin dependent
tunneling through MgO barriers is only beginning to be unravelled. Using planar
magnetic tunnel junctions in which ultra-thin layers of magnetic metals are
deposited in the middle of a MgO tunnel barrier here we demonstrate that the
TMR is strongly modified when these layers are discontinuous and composed of
small pancake shaped nanodots. At low temperatures, in the Coulomb blockade
regime, for layers less than ~1 nm thick, the conductance of the junction is
increased at low bias consistent with Kondo assisted tunneling. In the same
regime we observe a suppression of the TMR. For slightly thicker layers, and
correspondingly larger nanodots, the TMR is enhanced at low bias, consistent
with co-tunneling.

###Tunneling Magneto-Thermopower in Magnetic Tunnel Junctions|Carlos López-Monís,Alex Matos-Abiague,Jaroslav Fabian###

Tunneling Magneto-Thermopower in Magnetic Tunnel Junctions. Thermally induced spin-dependent transport across magnetic tunnel junctions
is theoretically investigated. We analyze the thermal analog of Slonczewski's
model (as well as its limiting case---Julliere's model) of tunneling
magnetoresistance and obtain analytical expressions for the junction
thermopower and the tunneling magneto-thermopower (TMT). The analytical model
is tested numerically for the special case of an Al$_2$O$_3$-based MTJ, for
which we analyze the dependence of the thermopower and TMT on the relative
magnetization orientations, as well as on the barrier height and thickness. We
show that at a certain barrier height TMT vanishes, separating the region of
positive and negative TMT. As its electrical prototype, this thermal spin
transport model should serve as a phenomenological benchmark for analyzing
experimental and first-principles calculations of thermopower in magnetic
tunnel junctions. The analytical expressions can be used as a first estimate of
the magneto-thermopower of the junctions using {\it ab initio} band structure
data of the junction ferromagnets.

###Spin-filter magnetoresistance in magnetic barrier junctions|Alireza Saffarzadeh###

Spin-filter magnetoresistance in magnetic barrier junctions. The tunnel current and magnetoresistance (TMR) are investigated in magnetic
tunnel junctions consisting of a spin-filter tunnel barrier, sandwiched between
a ferromagnetic (FM) electrode and a nonmagnetic (NM) electrode. The
investigations are based on the transfer matrix method and the free-electron
approximation. The numerical results show that the spin transport depends on
the relative magnetization orientation of the FM electrode and the spin-filter
barrier, such that the tunnel current reaches its maximum when the magnetic
moments of the FM electrode and the magnetic barrier are parallel. It is also
found that the TMR increases with increasing the applied voltage.

###A first-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions|Yoshio Miura,Shingo Muramoto,Kazutaka Abe,Masafumi Shirai###

A first-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions. We investigated the spin-dependent transport properties of Fe/MgAl2O4/Fe(001)
magnetic tunneling junctions (MTJs) on the basis of first-principles
calculations of the electronic structures and the ballistic conductance. The
calculated tunneling magnetoresistance (TMR) ratio of a Fe/MgAl2O4/Fe(001) MTJ
was about 160%, which was much smaller than that of a Fe/MgO/Fe(001) MTJ
(1600%) for the same barrier thickness. However, there was an evanescent state
with delta 1 symmetry in the energy gap around the Fermi level of normal spinel
MgAl2O4, indicating the possibility of a large TMR in Fe/MgAl2O4/Fe(001) MTJs.
The small TMR ratio of the Fe/MgAl2O4/Fe(001) MTJ was due to new conductive
channels in the minority spin states resulting from a band-folding effect in
the two-dimensional (2-D) Brillouin zone of the in-plane wave vector (k//) of
the Fe electrode. Since the in-plane cell size of MgAl2O4 is twice that of the
primitive in-plane cell size of bcc Fe, the bands in the boundary edges are
folded, and minority-spin states coupled with the delta 1 evanescent state in
the MgAl2O4 barrier appear at k//=0, which reduces the TMR ratio of the MTJs
significantly.

###Tremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe$_3$GaTe$_2$ with highly spin-polarized Fermi surfaces|Xinlu Li,Meng Zhu,Yaoyuan Wang,Fanxing Zheng,Jianting Dong,Ye Zhou,Long You,Jia Zhang###

Tremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe$_3$GaTe$_2$ with highly spin-polarized Fermi surfaces. Recently, van der Waals (vdW) magnetic heterostructures have received
increasing research attention in spintronics. However, the lack of
room-temperature magnetic order of vdW material has largely impedes its
development in practical spintronics devices. Inspired by the recently
discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic
order above room temperature and sizable perpendicular magnetic anisotropy, we
investigate the basic electronic structure and magnetic properties of Fe3GaTe2
as well as tunneling magnetoresistance effect in magnetic tunnel junctions
(MTJs) with structure of Fe3GaTe2/Insulator/Fe3GaTe2 by using first-principles
calculations. It is found that Fe3GaTe2 with highly spin-polarized Fermi
surface ensures that such magnetic tunnel junctions may have prominent
tunneling magnetoresistance effect at room temperature even comparable to
existing conventional AlOx and MgO-based MTJs. Our results suggest that
Fe3GaTe2-based MTJs may be the promising candidate for realizing long-waiting
full magnetic vdW spintronic devices.

###Tunneling magnetoresistance of perpendicular CoFeB-based junctions with exchange bias|Orestis Manos,Alexander Böhnke,Panagiota Bougiatioti,Robin Klett,Karsten Rott,Alessia Niesen,Jan-Michael Schmalhorst,Günter Reiss###

Tunneling magnetoresistance of perpendicular CoFeB-based junctions with exchange bias. Recently, magnetic tunnel junctions with perpendicular magnetized electrodes
combined with exchange bias films have attracted large interest. In this paper
we examine the tunnel magnetoresistance of
Ta/Pd/IrMn/Co-Fe/Ta/Co-Fe-B/MgO/Co-Fe-B/capping/Pd magnetic tunnel junctions in
dependence on the capping layer, i.e., Hf or Ta. In these stacks perpendicular
exchange bias fields of -500\,Oe along with perpendicular magnetic anisotropy
are combined. A tunnel magnetoresistance of $(47.2\pm 1.4)\%$ for the Hf-capped
sample was determined compared to the Ta one $(42.6\pm 0.7)\%$ at room
temperature. Interestingly, this observation is correlated to the higher boron
absorption of Hf compared to Ta which prevents the suppression of
$\Delta_{\textrm{1}}$ channel and leads to higher tunnel magnetoresistance
values. Furthermore, the temperature dependent coercivities of the soft
electrodes of both samples are mainly described by the Stoner-Wohlfarth model
including thermal fluctuations. Slight deviations at low temperatures can be
attributed to a torque on the soft electrode that is generated by the pinned
magnetic layer system.

###Large magnetoresistance in an electric field controlled antiferromagnetic tunnel junction|Yurong Su,Jia Zhang,Jing-Tao Lü,Jeongmin Hong,Long You###

Large magnetoresistance in an electric field controlled antiferromagnetic tunnel junction. Large magnetoresistance effect controlled by electric field rather than
magnetic field or electric current is a preferable routine for designing low
power consumption magnetoresistance-based spintronic devices. Here we propose
an electric-field controlled antiferromagnetic (AFM) tunnel junction with
structure of piezoelectric substrate/Mn3Pt/SrTiO3/Pt operating by the magnetic
phase transition (MPT) of antiferromagnet Mn3Pt through its magneto-volume
effect. The transport properties of the proposed AFM tunnel junction have been
investigated by employing first-principles calculations. Our results show that
a magnetoresistance over hundreds of percent is achievable when Mn3Pt undergoes
MPT from a collinear AFM state to a non-collinear AFM state. Band structure
analysis based on density functional calculations shows that the large TMR can
be attributed to the joint effect of significant different Fermi surface of
Mn3Pt at two AFM phases and the band symmetry filtering effect of the SrTiO3
tunnel barrier. In addition, other than single-crystalline tunnel barrier, we
also discuss the robustness of the proposed magnetoresistance effect by
considering amorphous AlOx barrier. Our results may open perspective way for
effectively electrical writing and reading of the AFM state and its application
in energy efficient magnetic memory devices.

###Giant oscillatory tunnel magnetoresistance in CoFe/MgO/CoFe(001) junctions|Thomas Scheike,Zhenchao Wen,Hiroaki Sukegawa,Seiji Mitani###

Giant oscillatory tunnel magnetoresistance in CoFe/MgO/CoFe(001) junctions. The tunnel magnetoresistance (TMR) effect observed in magnetic tunnel
junctions (MTJs) is commonly used in many spintronic applications because the
effect can easily convert from local magnetic states to electric signals in a
wide range of device resistances. In this study, we demonstrated TMR ratios of
up to 631% at room temperature (RT), which is two or more times larger than
those used currently for magnetoresistive random access memory (MRAM) devices,
using CoFe/MgO/CoFe(001) epitaxial MTJs. The TMR ratio increased up to 1143% at
10 K, which corresponds to an effective tunneling spin polarization of 0.923.
The observed large TMR ratios resulted from the fine-tuning of atomic-scale
structures of the MTJs, such as crystallographic orientations and MgO interface
oxidation, in which the well-known Delta1 coherent tunneling mechanism for the
giant TMR effect is expected to be pronounced. However, behavior that is not
covered by the standard coherent tunneling theory was unexpectedly manifested;
i.e., (i) TMR saturation at a thick MgO barrier region and (ii) enhanced TMR
oscillation with a 0.32 nm period in MgO thickness. Particularly, the TMR
oscillatory behavior dominates the transport in a wide range of MgO
thicknesses; the peak-to-valley difference of the TMR oscillation exceeded 140%
at RT, attributable to the appearance of large oscillatory components in
resistance area product (RA). Further, we found that the oscillatory behaviors
of the TMR ratio and RA survive, even under a +-1 V bias voltage application,
indicating the robustness of the oscillation. Our demonstration of the giant
RT-TMR ratio will be an essential step for establishing spintronic
architectures, such as large-capacity MRAMs and spintronic artificial neural
networks. More essentially, the present observations can trigger us to revisit
the true TMR mechanism in crystalline MTJs.

###Machine learning analysis of tunnel magnetoresistance of magnetic tunnel junctions with disordered MgAl2O4|Shenghong Ju,Yoshio Miura,Kaoru Yamamoto,Keisuke Masuda,Ken-ichi Uchida,Junichiro Shiomi###

Machine learning analysis of tunnel magnetoresistance of magnetic tunnel junctions with disordered MgAl2O4. Through Bayesian optimization and the least absolute shrinkage and selection
operator (LASSO) technique combined with first-principles calculations, we
investigated the tunnel magnetoresistance (TMR) effect of
Fe/disordered-MgAl2O4(MAO)/Fe(001) magnetic tunnel junctions (MTJs) to
determine structures of disordered-MAO that give large TMR ratios. The optimal
structure with the largest TMR ratio was obtained by Bayesian optimization with
1728 structural candidates, where the convergence was reached within 300
structure calculations. Characterization of the obtained structures suggested
that the in-plane distance between two Al atoms plays an important role in
determining the TMR ratio. Since the Al-Al distance of disordered MAO
significantly affects the imaginary part of complex band structures, the
majority-spin conductance of the {\Delta}1 state in Fe/disordered-MAO/Fe MTJs
increases with increasing in-plane Al-Al distance, leading to larger TMR
ratios. Furthermore, we found that the TMR ratio tended to be large when the
ratio of the number of Al, Mg, and vacancies in the [001] plane was 2:1:1,
indicating that the control of Al atomic positions is essential to enhancing
the TMR ratio in MTJs with disordered MAO. The present work reveals the
effectiveness and advantage of material informatics combined with
first-principles transport calculations in designing high-performance
spintronic devices based on MTJs.

###Theoretical study on magnetic tunneling junctions with semiconductor barriers CuInSe$_2$ and CuGaSe$_2$ including a detailed analysis of band-resolved transmittances|Keisuke Masuda,Yoshio Miura###

Theoretical study on magnetic tunneling junctions with semiconductor barriers CuInSe$_2$ and CuGaSe$_2$ including a detailed analysis of band-resolved transmittances. We study spin-dependent transport properties in magnetic tunneling junctions
(MTJs) with semiconductor barriers, Fe/CuInSe$_2$/Fe(001) and
Fe/CuGaSe$_2$/Fe(001). By analyzing their transmittances at zero bias voltage
on the basis of the first-principles calculations, we find that spin-dependent
coherent tunneling transport of $\Delta_1$ wave functions yields a relatively
high magnetoresistance (MR) ratio in both the MTJs. We carry out a detailed
analysis of the band-resolved transmittances in both the MTJs and find an
absence of the selective transmission of $\Delta_1$ wave functions in some
energy regions a few eV away from the Fermi level due to small band gaps in
CuInSe$_2$ and CuGaSe$_2$.

###Tunneling magnetoresistance in trilayer structures composed of group-IV ferromagnetic semiconductor Ge1-xFex, MgO, and Fe|Yuki K. Wakabayashi,Kohei Okamoto,Yoshisuke Ban,Shoichi Sato,Masaaki Tanaka,Shinobu Ohya###

Tunneling magnetoresistance in trilayer structures composed of group-IV ferromagnetic semiconductor Ge1-xFex, MgO, and Fe. Group-IV-based ferromagnetic semiconductor Ge1-xFex (GeFe) is one of the most
promising materials for efficient spin injectors and detectors for Si and Ge.
Recent first principles calculations (Sakamoto et al., Ref. 9) suggested that
the Fermi level is located in two overlapping largely spin-polarized bands
formed in the bandgap of GeFe; spin-down d(e) band and spin-up p-d(t2) band.
Thus, it is important to clarify how these bands contribute to spin injection
and detection. In this study, we show the first successful observation of the
tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs)
containing a group-IV ferromagnetic semiconductor, that is, in MTJs composed of
epitaxially grown Fe/MgO/Ge0.935Fe0.065. We find that the p-d(t2) band in GeFe
is mainly responsible for the tunneling transport. Although the obtained TMR
ratio is small (0.3%), the TMR ratio is expected to be enhanced by suppressing
leak current through amorphous-like crystal domains observed in MgO.

###In-Plane Magnetoresistance on the Surface of Topological Insulator|Morteza Salehi,Mohammad Alidoust,Yousef Rahnavard,Gholamreza Rashedi###

In-Plane Magnetoresistance on the Surface of Topological Insulator. We study the tunneling magneto-transport properties of the Ferromagnetic
Insulator-Normal Insulator-Ferromagnetic Insulator(F$\mid$N$\mid$F) and
Ferromagnetic Insulator-Barrier Insulator-Ferromagnetic Insulator
(F$\mid$B$\mid$F) junctions on the surface of topological insulator in which
in-plane magnetization directions of both ferromagnetic sides can be parallel
and antiparallel. We derive analytical expressions for electronic conductances
of the two mentioned junctions with both parallel and antiparallel directions
of magnetization and using them calculate magnetoresistance of the two
junctions. We use thin barrier approximation for investigating the
F$\mid$B$\mid$F junction. We find that although magnetoresistance of the
F$\mid$N$\mid$F and F$\mid$B$\mid$F junctions are tunable by changing the
strength of magnetization texture, they show different behaviors with variation
of magnetization. In contrast to the magnetoresistance of F$\mid$N$\mid$F,
magnetoresistance of F$\mid$B$\mid$F junctions shows very smooth enhance by
increasing the strength of magnetization. We suggest an experimental set up to
detect our predicted effects.

###Integration of antiferromagnetic Heusler compound Ru$_2$MnGe into spintronic devices|Jan Balluff,Teodor Huminiuc,Markus Meinert,Atsufumi Hirohata,Günter Reiss###

Integration of antiferromagnetic Heusler compound Ru$_2$MnGe into spintronic devices. We report on the first integration of an antiferromagnetic Heusler compound
acting as a pinning layer into magnetic tunneling junctions. The
antiferromagnet Ru$_2$MnGe is used to pin the magnetization direction of a
ferromagnetic Fe layer in MgO based thin film tunnelling magnetoresistance
stacks. The samples were prepared using magnetron co-sputtering. We investigate
the structural properties by X-ray diffraction and reflection, as well as
atomic force and high-resolution transmission electron microscopy. We find an
excellent crystal growth quality with low interface roughnesses of 1-3 \r{A},
which is crucial for the preparation of working tunnelling barriers. Using Fe
as a ferromagnetic electrode material we prepared magnetic tunneling junctions
and measured the magnetoresistance. We find a sizeable maximum
magnetoresistance value of 135%, which is comparable to other common Fe based
MTJ systems.

###Interfacial giant tunnel magnetoresistance and bulk-induced large perpendicular magnetic anisotropy in (111)-oriented junctions with fcc ferromagnetic alloys: A first-principles study|Keisuke Masuda,Hiroyoshi Itoh,Yoshiaki Sonobe,Hiroaki Sukegawa,Seiji Mitani,Yoshio Miura###

Interfacial giant tunnel magnetoresistance and bulk-induced large perpendicular magnetic anisotropy in (111)-oriented junctions with fcc ferromagnetic alloys: A first-principles study. We study the tunnel magnetoresistance (TMR) effect and magnetocrystalline
anisotropy in a series of magnetic tunnel junctions (MTJs) with $L1_1$-ordered
fcc ferromagnetic alloys and MgO barrier along the [111] direction. Considering
the (111)-oriented MTJs with different $L1_1$ alloys, we calculate their TMR
ratios and magnetocrystalline anisotropies on the basis of the first-principles
calculations. The analysis shows that the MTJs with Co-based alloys (CoNi,
CoPt, and CoPd) have high TMR ratios over 2000$\%$. These MTJs have
energetically favored Co-O interfaces where interfacial antibonding between Co
$d$ and O $p$ states is formed around the Fermi level. We find that the
resonant tunneling of the antibonding states, called the interface resonant
tunneling, is the origin of the obtained high TMR ratios. Our calculation of
the magnetocrystalline anisotropy shows that many $L1_1$ alloys have large
perpendicular magnetic anisotropy (PMA). In particular, CoPt has the largest
value of anisotropy energy $K_{\rm u} \approx 10\,{\rm MJ/m^3}$. We further
conduct a perturbation analysis of the PMA with respect to the spin-orbit
interaction and reveal that the large PMA in CoPt and CoNi mainly originates
from spin-conserving perturbation processes around the Fermi level.

###Current-driven Magnetization Reversal in a Ferromagnetic Semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As Tunnel Junction|D. Chiba,Y. Sato,T. Kita,F. Matsukura,H. Ohno###

Current-driven Magnetization Reversal in a Ferromagnetic Semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As Tunnel Junction. Current-driven magnetization reversal in a ferromagnetic semiconductor based
(Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K.
Magnetoresistance measurements combined with current pulse application on a
rectangular 1.5 x 0.3 um^2 device revealed that magnetization switching occurs
at low critical current densities of 1.1 - 2.2 x 10^5 A/cm^2 despite the
presence of spin-orbit interaction in the p-type semiconductor system. Possible
mechanisms responsible for the effect are discussed.

###Canted Magnetization Texture in Ferromagnetic Tunnel Junctions|Igor Kuzmenko,Vladimir Fal'ko###

Canted Magnetization Texture in Ferromagnetic Tunnel Junctions. We study the formation of inhomogeneous magnetization texture in the vicinity
of a tunnel junction between two ferromagnetic wires nominally in the
antiparallel configuration and its influence on the magnetoresistance of such a
device. The texture, dependent on magnetization rigidity and crystalline
anisotropy energy in the ferromagnet, appears upon an increase of ferromagnetic
inter-wire coupling above a critical value and it varies with an external
magnetic field.

###Tunneling magnetoresistance devices based on topological insulators: Ferromagnet/insulator/topological-insulator junctions employing Bi$_{2}$Se$_{3}$|Matthias Götte,Tomi Paananen,Günter Reiss,Thomas Dahm###

Tunneling magnetoresistance devices based on topological insulators: Ferromagnet/insulator/topological-insulator junctions employing Bi$_{2}$Se$_{3}$. We theoretically investigate tunneling magnetoresistance (TMR) devices, which
are probing the spin-momentum coupled nature of surface states of the
three-dimensional topological insulator Bi$_{2}$Se$_{3}$. Theoretical
calculations are performed based on a realistic tight-binding model for
Bi$_{2}$Se$_{3}$. We study both three dimensional devices, which exploit the
surface states of Bi$_{2}$Se$_{3}$, as well as two-dimensional devices, which
exploit the edge states of thin Bi$_{2}$Se$_{3}$ strips. We demonstrate that
the material properties of Bi$_{2}$Se$_{3}$ allow a TMR ratio at room
temperature of the order of 1000%. Analytical formulas are derived that allow a
quick estimate of the achievable TMR ratio in these devices. The devices can be
used to measure the spin polarization of the topological surface states as an
alternative to spin-ARPES. Unlike TMR devices based on magnetic tunnel
junctions the present devices avoid the use of a second ferromagnetic electrode
whose magnetization needs to be pinned.

###Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers|Bowei Zhou,Pravin Khanal,Onri Jay Benally,Deyuan Lyu,Daniel B. Gopman,Arthur Enriquez,Ali Habiboglu,Kennedy Warrilow,Jian-Ping Wang,Wei-Gang Wang###

Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers. Nb and its compounds are widely used in quantum computing due to their high
superconducting transition temperatures and high critical fields. Devices that
combine superconducting performance and spintronic non-volatility could deliver
unique functionality. Here we report the study of magnetic tunnel junctions
with Nb as the heavy metal layers. An interfacial perpendicular magnetic
anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO
heterostructures. The tunneling magnetoresistance was evaluated in junctions
with different thickness combinations and different annealing conditions. An
optimized magnetoresistance of 120% was obtained at room temperature, with a
damping parameter of 0.011 determined by ferromagnetic resonance. In addition,
spin-transfer torque switching has also been successfully observed in these
junctions with a quasistatic switching current density of 7.3*10^5 A/cm2.

###Inelastic electron tunneling spectroscopy of local "spin accumulation" devices|Holly N. Tinkey,Pengke Li,Ian Appelbaum###

Inelastic electron tunneling spectroscopy of local "spin accumulation" devices. We investigate the origin of purported "spin accumulation" signals observed
in local "three-terminal" (3T) measurements of ferromagnet/insulator/n-Si
tunnel junctions using inelastic electron tunneling spectroscopy (IETS).
Voltage bias and magnetic field dependences of the IET spectra were found to
account for the dominant contribution to 3T magnetoresistance signals, thus
indicating that it arises from inelastic tunneling through impurities and
defects at junction interfaces and within the barrier, rather than from spin
accumulation due to pure elastic tunneling into bulk Si as has been previously
assumed.

###Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric CoxMnyGez (x : z = 2 : 0.38) Heusler thin films|Siham Ouardi,Gerhard H. Fecher,Stanislav Chadov,Claudia Felser,Benjamin Balke,Xenia Kozina,Tomoyuki Taira,Masafumi Yamamoto###

Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric CoxMnyGez (x : z = 2 : 0.38) Heusler thin films. Fully epitaxial magnetic tunnel junctions (MTJs) with off-stoichiometric
Co2-based Heusler alloy shows a intense dependency of the tunnel
magnetoresistance (TMR) on the Mn composition, demonstrating giant TMR ratios
of up to 1995% at 4.2 K for 1. This work reports on the electronic structure of
non-stoichiometric CoxMnyGez thin films with a fixed Co/Ge ratio of x : z = 2 :
0.38. The electronic structure was investigated by high energy, hard X-ray
photoelectron spectroscopy combined with first-principles calculations. The
high-resolution measurements of the valence band of the non-stoichiometric
CoxMnyGez films close to the Fermi energy indicate a shift of the spectral
weight compared to bulk Co2MnGe. This is in agreement with the changes in the
density of states predicted by the calculations. Furthermore it is shown that
the co-sputtering of Co2MnGe together with additional Mn is an appropriate
technique to adjust the stoichiometry of the CoxMnyGez film composition. The
resulting changes of the electronic structure within the valence band will
allow to tune the magnetoresistive characteristics of CoxMnyGez based tunnel
junctions as verified by the calculations and photoemission experiments.

###Magnetic properties of epitaxial Fe$_3$O$_4$ films with various crystal orientations and TMR effect in room temperature|Taro Nagahama,Yuya Matsuda,Kazuya Tate,Shungo Hiratani,Yusuke Watanabe,Takashi Yanase,Toshihiro Shimada###

Magnetic properties of epitaxial Fe$_3$O$_4$ films with various crystal orientations and TMR effect in room temperature. Fe$_3$O$_4$ is a ferrimagnetic spinel ferrite that exhibits electric
conductivity at room temperature (RT). Although the material has been predicted
to be a half metal according to ab-initio calculations, magnetic tunnel
junctions (MTJs) with Fe$_3$O$_4$ electrodes have demonstrated a small tunnel
magnetoresistance effect. Not even the sign of the TMR ratio has been
experimentally established. Here, we report on the magnetic properties of
epitaxial Fe$_3$O$_4$ films with various crystal orientations. The films
exhibited apparent crystal orientation dependence on hysteresis curves. In
particular, Fe$_3$O$_4$(110) films exhibited in-plane uniaxial magnetic
anisotropy. With respect to the squareness of hysteresis, Fe$_3$O$_4$ (111)
demonstrated the largest squareness. Furthermore, we fabricated MTJs with
Fe$_3$O$_4$(110) electrodes, and obtained an TMR effect of -12\% at RT. The
negative TMR ratio corresponded to the negative spin polarization of
Fe$_3$O$_4$ predicted from band calculations.

###Picosecond Switching of Optomagnetic Tunnel Junctions|Luding Wang,Houyi Cheng,Pingzhi Li,Yang Liu,Youri L. W. van Hees,Reinoud Lavrijsen,Xiaoyang Lin,Kaihua Cao,Bert Koopmans,Weisheng Zhao###

Picosecond Switching of Optomagnetic Tunnel Junctions. Perpendicular magnetic tunnel junctions are one of the building blocks for
spintronic memories, which allow fast nonvolatile data access, offering
substantial potentials to revolutionize the mainstream computing architecture.
However, conventional switching mechanisms of such devices are fundamentally
hindered by spin polarized currents4, either spin transfer torque or spin orbit
torque with spin precession time limitation and excessive power dissipation.
These physical constraints significantly stimulate the advancement of modern
spintronics. Here, we report an optomagnetic tunnel junction using a
spintronic-photonic combination. This composite device incorporates an
all-optically switchable Co/Gd bilayer coupled to a CoFeB/MgO-based
perpendicular magnetic tunnel junction by the Ruderman-Kittel-Kasuya-Yosida
interaction. A picosecond all-optical operation of the optomagnetic tunnel
junction is explicitly confirmed by time-resolved measurements. Moreover, the
device shows a considerable tunnel magnetoresistance and thermal stability.
This proof-of-concept device represents an essential step towards ultrafast
spintronic memories with THz data access, as well as ultralow power
consumption.

###Oxide spintronics|Manuel Bibes,Agnes Barthelemy###

Oxide spintronics. Concomitant with the development of metal-based spintronics in the late
1980's and 1990's, important advances were made on the growth of high-quality
oxide thin films and heterostructures. While this was at first motivated by the
discovery of high-temperature superconductivity in perovskite Cu oxides, this
technological breakthrough was soon applied to other transition metal oxides,
and notably mixed-valence manganites. The discovery of colossal
magnetoresistance in manganite films triggered an intense research activity on
these materials, but the first notable impact of magnetic oxides in the field
of spintronics was the use of such manganites as electrodes in magnetic tunnel
junctions, yielding tunnel magnetoresistance ratios one order of magnitude
larger than what had been obtained with transition metal electrodes. Since
then, the research on oxide spintronics has been intense with the latest
developments focused on diluted magnetic oxides and more recently on
multiferroics. In this paper, we will review the most important results on
oxide spintronics, emphasizing materials physics as well as spin-dependent
transport phenomena, and finally give some perspectives on how the flurry of
new magnetic oxides could be useful for next-generation spintronics devices.

###Impact of lattice strain on the tunnel magneto-resistance in Fe/Insulator/Fe and Fe/Insulator/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ magnetic tunnel junctions|Y. Saeed,N. Singh,N. Useinov,U. Schwingenschlögl###

Impact of lattice strain on the tunnel magneto-resistance in Fe/Insulator/Fe and Fe/Insulator/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ magnetic tunnel junctions. The objective of this work is to describe the tunnel electron current in
single barrier magnetic tunnel junctions within a new approach that goes beyond
the single-band transport model. We propose a ballistic multi-channel electron
transport model that can explain the influence of in-plane lattice strain on
the tunnel magnetoresistance as well as the asymmetric voltage behavior. We
consider as an example single crystal magnetic Fe(110) electrodes for
Fe/Insulator/Fe and Fe/Insulator/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ tunnel
junctions, where the electronic band structures of Fe and
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ are derived by \it{ab-initio} calculations.

###Tunnel magnetoresistance and temperature related effects in magnetic tunnel junctions with embedded nanoparticles|Arthur Useinov,Chih-Huang Lai###

Tunnel magnetoresistance and temperature related effects in magnetic tunnel junctions with embedded nanoparticles. Temperature dependence of the tunnel magnetoresistance (TMR) was calculated
in range of the quantum-ballistic model in the magnetic tunnel junctions (MTJs)
with embedded nanoparticles (NPs). The electron tunnel transport through NP was
simulated in range of double barrier approach, which was integrated into the
model of the magnetic point-like contact. The resonant TMR conditions and
temperature impact were explored in detail. Moreover, the possible reasons of
the temperature induced resonant conditions were discussed in the range of the
lead-tunneling cell-lead model near Kondo temperature. We also found that
redistribution of the voltage drop becomes crucial in this model. Furthermore,
the direct tunneling plays the dominant role and cannot be omitted in the
quantum systems with the total tunneling thickness up to 5-6 nm. Hence, Coulomb
blockade model cannot explain Kondo-induced TMR anomalies in nanometer-sized
tunnel junctions.

###Determination of spin-orbit torque efficiencies in heterostructures with in-plane magnetic anisotropy|Yan-Ting Liu,Tian-Yue Chen,Tzu-Hsiang Lo,Tsung-Yu Tsai,Shan-Yi Yang,Yao-Jen Chang,Jeng-Hua Wei,Chi-Feng Pai###

Determination of spin-orbit torque efficiencies in heterostructures with in-plane magnetic anisotropy. It has been shown that the spin Hall effect from heavy transition metals can
generate sufficient spin-orbit torque and further produce current-induced
magnetization switching in the adjacent ferromagnetic layer. However, if the
ferromagnetic layer has in-plane magnetic anisotropy, probing such switching
phenomenon typically relies on tunneling magnetoresistance measurement of
nano-sized magnetic tunnel junctions, differential planar Hall voltage
measurement, or Kerr imaging approaches. We show that in magnetic
heterostructures with spin Hall metals, there exist current-induced in-plane
spin Hall effective fields and unidirectional magnetoresistance that will
modify their anisotropic magnetoresistance behavior. We also demonstrate that
by analyzing the response of anisotropic magnetoresistance under such
influences, one can directly and electrically probe magnetization switching
driven by the spin-orbit torque, even in micron-sized devices. This pump-probe
method allows for efficient and direct determination of key parameters from
spin-orbit torque switching events without lengthy device fabrication
processes.

###I-V curves of Fe/MgO (001) single- and double-barrier tunnel junctions|J. Peralta-Ramos,A. M. Llois,I. Rungger,S. Sanvito###

I-V curves of Fe/MgO (001) single- and double-barrier tunnel junctions. In this work, we calculate with ab initio methods the current-voltage
characteristics for ideal single- and double-barrier Fe/MgO (001) magnetic
tunnel junctions. The current is calculated in the phase-coherent limit by
using the recently developed SMEAGOL code, combining the nonequilibrium Green
function formalism with density-functional theory. In general we find that
double-barrier junctions display a larger magnetoresistance, which decays with
bias at a slower pace than their single-barrier counterparts. This is explained
in terms of enhanced spin filtering from the middle Fe layer sandwiched in
between the two MgO barriers. In addition, for double-barrier tunnel junctions,
we find a well defined peak in the magnetoresistance at a voltage of V=0.1 V.
This is the signature of resonant tunneling across a majority quantum well
state. Our findings are discussed in relation to recent experiments.

###Skyrmion meets magnetic tunnel junction: an efficient way for electrical skyrmion detection investigated by ab initio theory|Jonas Friedrich Schäfer-Richarz,Philipp Risius,Michael Czerner,Christian Heiliger###

Skyrmion meets magnetic tunnel junction: an efficient way for electrical skyrmion detection investigated by ab initio theory. In our proof-of-principle study we examine the influence of skyrmions on
magnetoresistive transport. In particular, we show that magnetic tunnel
junctions are a technologically appealing and promising way for electrical
detection of non-collinear magnetic structures. The calculated effect is shown
to originate from scattering between different k-states and cannot be
identified through densities of states alone. Our results suggest that the
detection efficiency strongly depends on the utilized materials.

###Dielectric breakdown in underoxidized magnetic tunnel junctions: Dependence on oxidation time and area|J. Ventura,R. Ferreira,J. B. Sousa,P. P. Freitas###

Dielectric breakdown in underoxidized magnetic tunnel junctions: Dependence on oxidation time and area. Magnetic tunnel junctions (MTJs) with partially oxidized 9 \AA
AlO$_x$-barriers were recently shown to have the necessary characteristics to
be used as magnetoresistive sensors in high-density storage devices. Here we
study dielectric breakdown in such underoxidized magnetic tunnel junctions,
focusing on its dependence on tunnel junction area and oxidation time. A clear
relation between breakdown mechanism and junction area is observed for the MTJs
with the highest studied oxidation time: samples with large areas fail usually
due to extrinsic causes (characterized by a smooth resistance decrease at
dielectric breakdown). Small area junctions fail mainly through an intrinsic
mechanism (sharp resistance decrease at breakdown). However, this dependence
changes for lower oxidation times, with extrinsic breakdown becoming dominant.
In fact, in the extremely underoxidized magnetic tunnel junctions, failure is
exclusively related with extrinsic causes, independently of MTJ-area. These
results are related with the presence of defects in the barrier (weak spots
that lead to intrinsic breakdown) and of metallic unoxidized Al
nanoconstrictions (leading to extrinsic breakdown).

###Spin-polarized tunneling through randomly transparent magnetic junctions: Reentrant magnetoresistance approaching the Julliere limit|Grigory Tkachov,Klaus Richter###

Spin-polarized tunneling through randomly transparent magnetic junctions: Reentrant magnetoresistance approaching the Julliere limit. Electron conductance in planar magnetic tunnel junctions with long-range
barrier disorder is studied within Glauber-eikonal approximation enabling exact
disorder ensemble averaging by means of the Holtsmark-Markov method. This
allows us to address a hitherto unexplored regime of the tunneling
magnetoresistance effect characterized by the crossover from
momentum-conserving to random tunneling as a function of the defect
concentration. We demonstrate that such a crossover results in a reentrant
magnetoresistance: It goes through a pronounced minimum before reaching
disorder- and geometry-independent Julliere's value at high defect
concentrations.

###First-principles study on magnetic tunneling junctions with semiconducting CuInSe${}_{2}$ and CuGaSe${}_{2}$ barriers|Keisuke Masuda,Yoshio Miura###

First-principles study on magnetic tunneling junctions with semiconducting CuInSe${}_{2}$ and CuGaSe${}_{2}$ barriers. We theoretically investigate two different magnetic tunneling junctions
(MTJs) with semiconductor barriers, CuInSe${}_{2}$ (CIS) and CuGaSe${}_{2}$
(CGS), which are the terminal compounds of recently reported mixed
semiconductor barrier, CuIn${}_{1-x}$Ga$_{\it x}$Se${}_{2}$. To discuss the
transport properties of these systems, we analyze complex band structures,
magnetoresistance (MR) ratios, and resistance-area products ($RA$) by using
first-principles based calculations in combination with the Landauer formula.
It is found that the $\Delta_{1}$ wave functions have dominant contributions to
the spin-dependent tunneling transport in both CIS- and CGS-based MTJs. We also
find that the CGS-based MTJ has a much larger MR ratio and slightly higher $RA$
than those of the CIS-based MTJ, which indicates that a larger MR ratio is
expected for a higher Ga concentration $x$ in the
CuIn${}_{1-x}$Ga${}_{x}$Se${}_{2}$-based MTJs. We further study the
relationship between the band gaps in the barriers and MR ratios by changing
the Coulomb repulsions in the Cu 3$d$ states of the CIS and CGS. It is shown
that the barrier with a larger band gap yields a larger MR ratio. The
comparison of MR ratios and $RA$ between the CIS-, CGS-, and MgO-based MTJs are
also given.

###Magnetoresistive junctions based on epitaxial graphene and hexagonal boron nitride|Oleg V. Yazyev,Alfredo Pasquarello###

Magnetoresistive junctions based on epitaxial graphene and hexagonal boron nitride. We propose monolayer epitaxial graphene and hexagonal boron nitride (h-BN) as
ultimate thickness covalent spacers for magnetoresistive junctions. Using a
first-principles approach, we investigate the structural, magnetic and spin
transport properties of such junctions based on structurally well defined
interfaces with (111) fcc or (0001) hcp ferromagnetic transition metals. We
find low resistance area products, strong exchange couplings across the
interface, and magnetoresistance ratios exceeding 100% for certain chemical
compositions. These properties can be fine tuned, making the proposed junctions
attractive for nanoscale spintronics applications.

###Exchange bias effect in martensitic epitaxial Ni-Mn-Sn thin films applied to pin CoFeB/MgO/CoFeB magnetic tunnel junctions|Niclas Teichert,Alexander Boehnke,Anna Behler,Bruno Weise,Anja Waske,Andreas Hütten###

Exchange bias effect in martensitic epitaxial Ni-Mn-Sn thin films applied to pin CoFeB/MgO/CoFeB magnetic tunnel junctions. The exchange bias effect is commonly used to shift the coercive field of a
ferromagnet. This technique is crucial for the use of magnetic tunnel junctions
as logic or memory devices. Therefore, an independent switching of the two
ferromagnetic electrodes is necessary to guarantee a reliable readout. Here, we
demonstrate that the intrinsic exchange bias effect of Ni-Mn-Sn can be used to
apply a unidirectional anisotropy to magnetic tunnel junctions. For this, we
use epitaxial Ni-Mn-Sn films as pinning layers for microfabricated
CoFeB/MgO/CoFeB magnetic tunnel junctions. We compare the exchange bias field
($H_{\text{EB}}$) measured after field cooling in $-10$\,kOe external field by
magnetization measurements with $H_{\text{EB}}$ obtained from tunnel
magnetoresistance measurements. Consistent for both methods we find an exchange
bias of about $H_{\text{EB}}=130$\,Oe at 10\,K, which decreases with increasing
temperature and vanishes above 70\,K.

###Spintronics with NSN Junction of one-dimensional quantum wires : A study of Pure Spin Current and Magnetoresistance|Sourin Das,Sumathi Rao,Arijit Saha###

Spintronics with NSN Junction of one-dimensional quantum wires : A study of Pure Spin Current and Magnetoresistance. We demonstrate possible scenarios for production of pure spin current and
large tunnelling magnetoresistance ratios from elastic co-tunnelling and
crossed Andreev reflection across a superconducting junction comprising of
normal metal-superconductor-normal metal, where, the normal metal is a
one-dimensional interacting quantum wire. We show that there are fixed points
in the theory which correspond to the case of pure spin current. We analyze the
influence of electron-electron interaction and see how it stabilizes or
de-stabilizes the production of pure spin current. These fixed points can be of
direct experimental relevance for spintronics application of normal
metal-superconductor-normal metal junctions of one-dimensional quantum wires.
We also calculate the power law temperature dependence of the crossed Andreev
reflection enhanced tunnelling magnetoresistance ratio for the normal
metal-superconductor-normal metal junction.

###High-field magnetoresistance of Fe/GaAs/Fe tunnel junctions|M. Zenger,J. Moser,W. Wegscheider,D. Weiss,T. Dietl###

High-field magnetoresistance of Fe/GaAs/Fe tunnel junctions. We investigate transport through 6 to 10 nm thin epitaxial GaAs(001) barriers
sandwiched between polycrystalline iron films. Apart from a pronounced
tunneling magnetoresistance effect (TMR) at low magnetic fields we observe a
distinct negative magnetoresistance (MR) at low and a positive MR at higher
temperatures. We show that the negative MR contribution is only observed for
the ferromagnetic iron contacts but is absent if iron is replaced by copper or
gold electrodes. Possible explanations of the negative MR involve suppression
of spin-flip scattering or Zeeman splitting of the tunneling barrier.

###Spin injection in a single metallic nanoparticle: a step towards nanospintronics|A. Bernand-Mantel,P. Seneor,N. Lidgi,M. Munoz,V. Cros,S. Fusil,K. Bouzehouane,C. Deranlot,A. Vaures,F. Petroff,A. Fert###

Spin injection in a single metallic nanoparticle: a step towards nanospintronics. We have fabricated nanometer sized magnetic tunnel junctions using a new
nanoindentation technique in order to study the transport properties of a
single metallic nanoparticle. Coulomb blockade effects show clear evidence for
single electron tunneling through a single 2.5 nm Au cluster. The observed
magnetoresistance is the signature of spin conservation during the transport
process through a non magnetic cluster.

###$Ab$ $Initio$ Study of Magnetic Tunnel Junctions Based on Half-Metallic and Spin-Gapless Semiconducting Heusler Compounds: Reconfigurable Diode and Inverse Tunnel-Magnetoresistance Effect|T. Aull,E. Şaşıoğlu,N. F. Hinsche,I. Mertig###

$Ab$ $Initio$ Study of Magnetic Tunnel Junctions Based on Half-Metallic and Spin-Gapless Semiconducting Heusler Compounds: Reconfigurable Diode and Inverse Tunnel-Magnetoresistance Effect. Magnetic tunnel junctions (MTJs) have attracted strong research interest
within the last decades due to their potential use as nonvolatile memory such
as MRAM as well as for magnetic logic applications. Half-metallic magnets
(HMMs) have been suggested as ideal electrode materials for MTJs to achieve an
extremely large tunnel-magnetoresistance (TMR) effect. Despite their high TMR
ratios, MTJs based on HMMs do not exhibit current rectification, i.e., a diode
effect, which was achieved in a magnetic tunnel junction concept based on HMMs
and type-II spin-gapless semiconductors (SGSs). The proposed concept has
recently been experimentally demonstrated using Heusler compounds. In the
present work, we investigate from first-principles MTJs based on type-II SGS
and HMM quaternary Heusler compounds FeVTaAl, FeVTiSi, MnVTiAl, and CoVTiSb.
Our $ab$ $initio$ quantum transport calculations based on a nonequilibrium
Green's function method have demonstrated that the MTJs under consideration
exhibit current rectification with relatively high on:off ratios. We show that,
in contrast to conventional semiconductor diodes, the rectification bias
voltage window (or breakdown voltage) of the MTJs is limited by the spin gap of
the HMM and SGS Heusler compounds. A unique feature of the present MTJs is that
the diode effect can be configured dynamically, i.e., depending on the relative
orientation of the magnetization of the electrodes, the MTJ allows the
electrical current to pass either in one or the other direction, which leads to
an inverse TMR effect. The combination of nonvolatility, reconfigurable diode
functionality, tunable rectification voltage window, and high Curie temperature
of the electrode materials makes the proposed MTJs very promising for
room-temperature spintronic applications and opens ways to magnetic memory and
logic concepts as well as logic-in-memory computing.

###Spin-Imbalance and Magnetoresistance in Ferromagnet/Superconductor/Ferromagnet Double Tunnel Junctions|S. Takahashi,H. Imamura,S. Maekawa###

Spin-Imbalance and Magnetoresistance in Ferromagnet/Superconductor/Ferromagnet Double Tunnel Junctions. We theoretically study the spin-dependent transport in a ferromagnet/super-
conductor/ferromagnet double tunnel junction. The tunneling current in the
antiferromagnetic alignment of the magnetizations gives rise to a spin
imbalance in the superconductor. The resulting nonequilibrium spin density
strongly suppresses the superconductivity with increase of bias voltage and
destroys it at a critical voltage Vc. The results provide a new method not only
for measuring the spin polarization of ferromagnets but also for controlling
superconductivity and tunnel magnetoresistance (TMR) by applying the bias
voltage.

###Effect of interface states on spin-dependent tunneling in Fe/MgO/Fe tunnel junctions|K. D. Belashchenko,J. Velev,E. Y. Tsymbal###

Effect of interface states on spin-dependent tunneling in Fe/MgO/Fe tunnel junctions. The electronic structure and spin-dependent tunneling in epitaxial
Fe/MgO/Fe(001) tunnel junctions are studied using first-principles
calculations. For small MgO barrier thickness the minority-spin resonant bands
at the two interfaces make a significant contribution to the tunneling
conductance for the antiparallel magnetization, whereas these bands are, in
practice, mismatched by disorder and/or small applied bias for the parallel
magnetization. This explains the experimentally observed decrease in tunneling
magnetoresistance (TMR) for thin MgO barriers. We predict that a monolayer of
Ag epitaxially deposited at the interface between Fe and MgO suppresses
tunneling through the interface band and may thus be used to enhance the TMR
for thin barriers.

###Spin torque, tunnel-current spin polarization and magnetoresistance in MgO magnetic tunnel junctions|G. D. Fuchs,J. A. Katine,S. I. Kiselev,D. Mauri,K. S. Wooley,D. C. Ralph,R. A. Buhrman###

Spin torque, tunnel-current spin polarization and magnetoresistance in MgO magnetic tunnel junctions. We examine the spin torque (ST) response of magnetic tunnel junctions (MTJs)
with ultra-thin MgO tunnel barrier layers to investigate the relationship
between the spin-transfer torque and the tunnel magnetoresistance (TMR) under
finite bias. We find that the spin torque per unit current exerted on the free
layer decreases by less than 10% over a bias range where the TMR decreases by
over 40%. We examine the implications of this result for various spin-polarized
tunneling models and find that it is consistent with magnetic-state-dependent
effective tunnel decay lengths.

###Large influence of capping layers on tunnel magnetoresistance in magnetic tunnel junctions|Jiaqi Zhou,Weisheng Zhao,Yin Wang,Shouzhong Peng,Junfeng Qiao,Li Su,Lang Zeng,Na Lei,Lei Liu,Youguang Zhang,Arnaud Bournel###

Large influence of capping layers on tunnel magnetoresistance in magnetic tunnel junctions. It has been reported in experiments that capping layers which enhance the
perpendicular magnetic anisotropy (PMA) of magnetic tunnel junctions (MTJs)
induce great impact on the tunnel magnetoresistance (TMR). To explore the
essential influence caused by capping layers, we carry out ab initio
calculations on TMR in the X(001)|CoFe(001)|MgO(001)|CoFe(001)|X(001) MTJ,
where X represents the capping layer material which can be tungsten, tantalum
or hafnium. We report TMR in different MTJs and demonstrate that tungsten is an
ideal candidate for a giant TMR ratio. The transmission spectrum in Brillouin
zone is presented. It can be seen that in the parallel condition of MTJ, sharp
transmission peaks appear in the minority-spin channel. This phenomenon is
attributed to the resonant tunnel transmission effect and we explained it by
the layer-resolved density of states (DOS). In order to explore transport
properties in MTJs, the density of scattering states (DOSS) was studied from
the point of band symmetry. It has been found that CoFe|tungsten interface
blocks scattering states transmission in the anti-parallel condition. This work
reports TMR and transport properties in MTJs with different capping layers, and
proves that tungsten is a proper capping layer material, which would benefit
the design and optimization of MTJs.

###Magnetoresistance in Co-hBN-NiFe tunnel junctions enhanced by resonant tunneling through single defects in ultrathin hBN barriers|Pablo U. Asshoff,Jose L. Sambricio,Sergey Slizovskiy,Aidan P. Rooney,Takashi Taniguchi,Kenji Watanabe,Sarah J. Haigh,Vladimir Fal'ko,Irina V. Grigorieva,Ivan J. Vera-Marun###

Magnetoresistance in Co-hBN-NiFe tunnel junctions enhanced by resonant tunneling through single defects in ultrathin hBN barriers. Hexagonal boron nitride (hBN) is a prototypical high-quality two-dimensional
insulator and an ideal material to study tunneling phenomena, as it can be
easily integrated in vertical van der Waals devices. For spintronic devices,
its potential has been demonstrated both for efficient spin injection in
lateral spin valves and as a barrier in magnetic tunnel junctions (MTJs). Here
we reveal the effect of point defects inevitably present in mechanically
exfoliated hBN on the tunnel magnetoresistance of Co-hBN-NiFe MTJs. We observe
a clear enhancement of both the conductance and magnetoresistance of the
junction at well-defined bias voltages, indicating resonant tunneling through
magnetic (spin-polarized) defect states. The spin polarization of the defect
states is attributed to exchange coupling of a paramagnetic impurity in the
few-atomic-layer thick hBN to the ferromagnetic electrodes. This is confirmed
by excellent agreement with theoretical modelling. Our findings should be taken
into account in analyzing tunneling processes in hBN-based magnetic devices.
More generally, our study shows the potential of using atomically thin hBN
barriers with defects to engineer the magnetoresistance of MTJs and to achieve
spin filtering, opening the door towards exploiting the spin degree of freedom
in current studies of point defects as quantum emitters.

###Control of sensitivity in vortex-type magnetic tunnel junction magnetometer sensors by the pinned layer geometry|Motoki Endo,Muftah Al-Mahdawi,Mikihiko Oogane,Yasuo Ando###

Control of sensitivity in vortex-type magnetic tunnel junction magnetometer sensors by the pinned layer geometry. The tuning of sensitivity and dynamic range in linear magnetic sensors is
required in various applications. We demonstrate the control and design of the
sensitivity in magnetic tunnel junction (MTJ) sensors with a vortex-type
sensing layer. In this work, we develop sensor MTJs with NiFe sensing layers
having a vortex magnetic configuration. We demonstrate that by varying the
pinned layer size, the sensitivity to magnetic field is tuned linearly. We
obtain a high magnetoresistance ratio of 140 %, and we demonstrate a
controllable sensitivity from 0.85 to 4.43 %/Oe, while keeping the vortex layer
fixed in size. We compare our experimental results with micromagnetic
simulations. We find that the linear displacement of vortex core by an applied
field makes the design of vortex sensors simple. The control of the pinned
layer geometry is an effective method to increase the sensitivity, without
affecting the vortex state of the sensing layer. Furthermore, we propose that
the location of the pinned layer can be used to realize more sensing
functionalities from a single sensor.

###Magnetic Diode Effect in Double Barrier Tunnel Junctions|M. Chshiev,D. Stoeffler,A. Vedyayev,K. Ounadjela###

Magnetic Diode Effect in Double Barrier Tunnel Junctions. A quantum statistical theory of spin-dependent tunneling through asymmetric
magnetic double barrier junctions is presented which describes $both$ ballistic
and diffuse tunneling by a single analytical expression. It is evidenced that
the key parameter for the transition between these two tunneling regimes is the
electron scattering. For these junctions a strong asymmetric behaviour in the
I-V characteristics and the tunnel magnetoresistance (TMR) is predicted which
can be controlled by an applied magnetic field. This phenomenon relates to the
quantum well states in the middle metallic layer. The corresponding resonances
in the current and the TMR are drastically phase shifted under positive and
negative voltage.

###Asymmetric Bias Dependence in Double Spin Filter Tunnel Junctions|G. X. Miao,J. S. Moodera###

Asymmetric Bias Dependence in Double Spin Filter Tunnel Junctions. In double spin filter (SF) tunnel junctions, the spin information is
generated and analyzed purely from the SF effect with nonmagnetic electrodes.
In this article we numerically evaluate the bias dependence of
magnetoresistance in such tunnel junctions (nonmagnetic metal / SF /
nonmagnetic insulator / SF / nonmagnetic metal), particularly in cases when
different SF materials are utilized. A large magnetoresistance with
nonmonotonic and asymmetric bias dependence is expected within the frame of WKB
approximation. We illustrate the systematic influence of tunnel barrier height,
tunnel barrier thickness, and exchange energy splitting on magnetoresistance,
particularly focusing on the asymmetric behavior of the magnetoresistance bias
dependence.

###Quantum-well tunneling anisotropic magnetoresistance above room temperature|Muftah Al-Mahdawi,Qingyi Xiang,Yoshio Miura,Mohamed Belmoubarik,Keisuke Masuda,Shinya Kasai,Hiroaki Sukegawa,Seiji Mitani###

Quantum-well tunneling anisotropic magnetoresistance above room temperature. Quantum-well (QW) devices have been extensively investigated in semiconductor
structures. More recently, spin-polarized QWs were integrated into magnetic
tunnel junctions (MTJs). In this work, we demonstrate the spin-based control of
the quantized states in iron $3d$-band QWs, as observed in experiments and
theoretical calculations. We find that the magnetization rotation in the Fe QWs
significantly shifts the QW quantization levels, which modulate the
resonant-tunneling current in MTJs, resulting in a tunneling anisotropic
magnetoresistance (TAMR) effect of QWs. This QW-TAMR effect is sizable compared
to other types of TAMR effect, and it is present above the room-temperature. In
a QW MTJ of Cr/Fe/MgAl$_2$O$_4$/top electrode, where the QW is formed by a
mismatch between Cr and Fe in the $d$ band with $\Delta_1$ symmetry, a QW-TAMR
ratio of up to 5.4 % was observed at 5 K, which persisted to 1.2 % even at
380K. The magnetic control of QW transport can open new applications for
spin-coupled optoelectronic devices, ultra-thin sensors, and memories.

###Tunneling anisotropic magnetoresistance in Fe/GaAs/Au junctions: orbital effects|M. Wimmer,M. Lobenhofer,J. Moser,A. Matos-Abiague,D. Schuh,W. Wegscheider,J. Fabian,K. Richter,D. Weiss###

Tunneling anisotropic magnetoresistance in Fe/GaAs/Au junctions: orbital effects. We report experiments on epitaxially grown Fe/GaAs/Au tunnel junctions
demonstrating that the tunneling anisotropic magnetoresistance (TAMR) effect
can be controlled by a magnetic field. Theoretical modelling shows that the
interplay of the orbital effects of a magnetic field and the Dresselhaus
spin-orbit coupling in the GaAs barrier leads to an independent contribution to
the TAMR effect with uniaxial symmetry, whereas the Bychkov-Rashba spin-orbit
coupling does not play a role. The effect is intrinsic to barriers with bulk
inversion asymmetry.

###Lattice Softening in Metastable bcc CoxMn100-x(001) Ferromagnetic Layers for a Strain-Less Magnetic Tunnel Junction|Kelvin Elphick,Kenta Yoshida,Tufan Roy,Tomohiro Ichinose,Kazuma Kunimatsu,Tomoki Tsuchiya,Masahito Tsujikawa,Yasuyoshi Nagai,Shigemi Mizukami,Masafumi Shirai,Atsufumi Hirohata###

Lattice Softening in Metastable bcc CoxMn100-x(001) Ferromagnetic Layers for a Strain-Less Magnetic Tunnel Junction. In spintronics, one of the long standing questions is why the MgO-based
magnetic tunnel junction (MTJ) is almost the only option to achieve a large
tunnelling magnetoresistance (TMR) ratio at room temperature (RT) but not as
large as the theoretical prediction. This study focuses on the development of
an almost strain-free MTJ using metastable bcc CoxMn100-x ferromagnetic films.
We have investigated the degree of crystallisation in MTJ consisting of
CoxMn100-x/MgO/CoxMn100-x (x = 66, 75, 83 and 86) in relation to their TMR
ratios. Cross-sectional high resolution transmission electron microscopy
(HRTEM) reveals that almost consistent lattice constants of these layers for 66
< x < 83 with maintaining large TMR ratios of 229% at RT, confirming the soft
nature of the CoxMn100-x layer with some dislocations at the MgO/Co75Mn25
interfaces. For x = 86, on the other hand, the TMR ratio is found to be reduced
to 142% at RT, which is partially attributed to the increased number of the
dislocations at the MgO/Co86Mn14 interfaces and amorphous grains identified in
the MgO barrier. Ab-initio calculations confirm the crystalline deformation
stability across a broad compositional range in CoMn, proving the advantage of
a strain-free interface for much larger TMR ratios.

###Voltage-tunable giant nonvolatile multiple-state resistance in interlayer-sliding ferroelectric h-BN engineered van der Waals multiferroic tunnel junction|Xinlong Dong,Xuemin Shen,Xiaowen Sun,Yuhao Bai,Zhi Yan,Xiaohong Xu###

Voltage-tunable giant nonvolatile multiple-state resistance in interlayer-sliding ferroelectric h-BN engineered van der Waals multiferroic tunnel junction. Multiferroic tunnel junctions (MFTJs) based on two-dimensional (2D) van der
Waals heterostructures with sharp and clean interfaces at the atomic scale are
crucial for applications in nanoscale multi-resistive logic memory devices. The
recently discovered sliding ferroelectricity in 2D van der Waals materials has
opened new avenues for ferroelectric-based devices. Here, we theoretically
investigate the spin-dependent electronic transport properties of
Fe$_3$GeTe$_2$/graphene/bilayer-$h$-BN/graphene/CrI$_3$ (FGT/Gr-BBN-Gr/CrI)
all-vdW MFTJs by employing the nonequilibrium Green's function combined with
density functional theory. We demonstrate that such FGT/Gr-BBN-Gr/CrI MFTJs
exhibit four non-volatile resistance states associated with different staking
orders of sliding ferroelectric BBN and magnetization alignment of
ferromagnetic free layer CrI$_3$, with a maximum tunnel magnetoresistance
(electroresistance) ratio, i.e., TMR (TER) up to $\sim$$3.36\times10^{4}$\%
($\sim$$6.68\times10^{3}$\%) at a specific bias voltage. Furthermore, the
perfect spin filtering and remarkable negative differential resistance effects
are evident in our MFTJs. We further discover that the TMR, TER, and spin
polarization ratio under an equilibrium state can be enhanced by the
application of in-plane biaxial strain. This work shows that the giant
tunneling resistance ratio, multiple resistance states, and excellent
spin-polarized transport properties of sliding ferroelectric BBN-based MFTJs
indicate its significant potential in nonvolatile memories.

###Tunneling Anisotropic Magnetoresistance in Co/AlOx/Au Tunnel Junctions|R. S. Liu,L. Michalak,C. M. Canali,L. Samuelson,H. Pettersson###

Tunneling Anisotropic Magnetoresistance in Co/AlOx/Au Tunnel Junctions. We observe spin-valve-like effects in nano-scaled thermally evaporated
Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and
depends on the relative orientation of the magnetization direction of the Co
electrode with respect to the current direction. We attribute this effect to a
two-step magnetization reversal and an anisotropic density of states resulting
from spin-orbit interaction. The results of this study points to future
applications of novel spintronics devices involving only one ferromagnetic
layer.

###Oxide layer boron leads to reduced symmetry spin filtering magnetic tunnel junctions|Derek A. Stewart###

Oxide layer boron leads to reduced symmetry spin filtering magnetic tunnel junctions. Experimental studies of FeCoB/MgO/FeCoB tunnel junctions indicate that boron
diffuses into MgO during rf-sputtering and forms polycrystalline Mg-B-O
regions. These tunnel junctions provide high tunneling magnetoresistance values
and low RA products. However the crystal structure of the Mg-B-O region remains
unknown. Using density functional techniques, I examine three potential Mg(B)
oxides including Mg$_{2}$B$_{2}$O$_{5}$ (monoclinic and triclinic) and the
orthorhombic mineral Kotoite (Mg$_3$B$_2$O$_6$). Kotoite is the best candidate
for formation in magnetic tunnel junctions. The (100) surface of Kotoite has a
good lattice match with (001) MgO and could template neighboring FeCo into bcc
layers during annealing. Complex band structure analysis of Kotoite shows that
the C$_{2v}$ $\tilde{\Delta}_1$ band has a much smaller imaginary k component
than the C$_{2v}$ $\tilde{\Delta}_4$ band. Based on symmetry analysis, the
majority spin $\Delta_1$ band in FeCo should couple well with the Kotoite
$\tilde{\Delta}_1$ band, while the minority FeCo $\Delta_5$ will couple
partially with the $\tilde{\Delta}_4$ band. Kotoite provides a new route to
high tunneling magnetoresistance based on spin filtering by a lower symmetry
oxide region.

###Magnetic tunnel junctions with ferroelectric barriers: Prediction of four resistance states from first-principles|Julian P. Velev,Chun-Gang Duan,J. D. Burton,Alexander Smogunov,Manish K. Niranjan,Erio Tosatti,S. S. Jaswal,Evgeny Y. Tsymbal###

Magnetic tunnel junctions with ferroelectric barriers: Prediction of four resistance states from first-principles. Magnetic tunnel junctions (MTJs), composed of two ferromagnetic electrodes
separated by a thin insulating barrier layer, are currently used in spintronic
devices, such as magnetic sensors and magnetic random access memories.
Recently, driven by demonstrations of ferroelectricity at the nanoscale,
thin-film ferroelectric barriers were proposed to extend the functionality of
MTJs. Due to the sensitivity of conductance to the magnetization alignment of
the electrodes (tunnelling magnetoresistance) and the polarization orientation
in the ferroelectric barrier (tunnelling electroresistance), these multiferroic
tunnel junctions (MFTJs) may serve as four-state resistance devices. Based on
first-principles calculations we demonstrate four resistance states in
SrRuO3/BaTiO3/SrRuO3 MFTJs with asymmetric interfaces. We find that the
resistance of such a MFTJ is significantly changed when the electric
polarization of the barrier is reversed and/or when the magnetizations of the
electrodes are switched from parallel to antiparallel. These results reveal the
exciting prospects of MFTJs for application as multifunctional spintronic
devices.

###Single-band tight-binding parameters for Fe-MgO-Fe magnetic heterostructures|Tehseen Z. Raza,Hassan Raza###

Single-band tight-binding parameters for Fe-MgO-Fe magnetic heterostructures. We present a computationally efficient transferable single-band tight-binding
model (SBTB) for spin polarized transport in heterostructures with an effort to
capture the band structure effects. As an example, we apply it to study
transport through Fe-MgO-Fe(100) magnetic tunnel junction devices. We propose a
novel approach to extract suitable tight-binding parameters for a material by
using the energy resolved transmission as the benchmark, which inherently has
the bandstructure effects over the two dimensional transverse Brillouin zone.
The SBTB parameters for each of the four symmetry bands for bcc Fe(100) are
first proposed which are complemented with the transferable tight-binding
parameters for the MgO tunnel barrier for the Delta_1 and Delta_5 bands. The
non-equilibrium Green's function formalism is then used to calculate the
transport. Features like I-V characteristics, voltage dependence and the
barrier width dependence of the tunnel magnetoresistance ratio are captured
quantitatively and the trends match well with the ones observed by ab initio
methods.

###Interface Magnetoresistance in Manganite-Titanate Heterojunctions|T. Susaki,N. Nakagawa,H. Y. Hwang###

Interface Magnetoresistance in Manganite-Titanate Heterojunctions. We have found that the current- voltage characteristics of
La0.7Sr0.3MnO3(-delta)/Nb:SrTiO3 rectifying junctions are quantitatively
well-described by (thermally-assisted) tunneling with an effectively
temperature-independent Schottky barrier under no magnetic field, while those
of the oxygen deficient junction remarkably deviate from such a simple behavior
as magnetic field is applied. These results indicate a new form of
magnetoresistance arising from magnetic field changes of the interface band
diagram via the strong electron-spin coupling in manganites.

###Tunneling magnetoresistance in devices based on epitaxial NiMnSb with uniaxial anisotropy|J. Liu,E. Girgis,P. Bach,C. Ruester,C. Gould,G. Schmidt,L. W. Molenkamp###

Tunneling magnetoresistance in devices based on epitaxial NiMnSb with uniaxial anisotropy. We demonstrate tunnel magnetoresistance (TMR) junctions based on a tri layer
system consisting of an epitaxial NiMnSb, aluminum oxide and CoFe tri layer.
The junctions show a tunnelling magnetoresistance of Delta R/R of 8.7% at room
temperature which increases to 14.7% at 4.2K. The layers show clear separate
switching and a small ferromagnetic coupling. A uniaxial in plane anisotropy in
the NiMnSb layer leads to different switching characteristics depending on the
direction in which the magnetic field is applied, an effect which can be used
for sensor applications.

###Magnetoresistance of the double-tunnel-junction Coulomb Blockade with magnetic metals|Kingshuk Majumdar,Selman Hershfield###

Magnetoresistance of the double-tunnel-junction Coulomb Blockade with magnetic metals. We have studied the Junction Magnetoresistance (JMR) and the Differential
junction magnetoresistance (DJMR) for double tunnel junctions with magnetic
metals in the Coulomb Blockade regime. Spikes are seen in both the JMR and the
DJMR vs. voltage curves. They occur at those places where the current increases
by a step. In all cases the large bias limit can be obtained by adding the
resistances of each of the junctions in series. The JMR is positive in all the
cases we studied, whereas the DJMR can be positive or negative as a function of
the voltage. Moreover, the relative variation of the DJMR as a function of the
voltage is larger than the variation of the JMR with the voltage.

###Spin filtering and magnetoresistance in ballistic tunnel junctions|J. C. Egues,C. Gould,G. Richter,L. W. Molenkamp###

Spin filtering and magnetoresistance in ballistic tunnel junctions. We theoretically investigate magnetoresistance (MR) effects in connection
with spin filtering in quantum-coherent transport through tunnel junctions
based on non-magnetic/semimagnetic heterostructures. We find that spin
filtering in conjunction with the suppression/enhancement of the spin-dependent
Fermi seas in semimagnetic contacts gives rise to (i) spin-split kinks in the
MR of single barriers and (ii) a robust beating pattern in the MR of double
barriers with a semimagnetic well. We believe these are unique signatures for
quantum filtering.

###Room-temperature and tunable tunneling magnetoresistance in Fe3GaTe2-based all-2D van der Waals heterojunctions with high spin polarization|Wen Jin,Gaojie Zhang,Hao Wu,Li Yang,Wenfeng Zhang,Haixin Chang###

Room-temperature and tunable tunneling magnetoresistance in Fe3GaTe2-based all-2D van der Waals heterojunctions with high spin polarization. Magnetic tunnel junctions (MTJs) based on all-two dimensional (2D) van der
Waals heterostructures with sharp and clean interfaces in atomic scale are
essential for the application of next-generation spintronics. However, the lack
of room-temperature intrinsic ferromagnetic crystals with perpendicular
magnetic anisotropy has greatly hindered the development of vertical MTJs. The
discovery of room-temperature intrinsic ferromagnetic 2D crystal Fe3GaTe2 has
solved the problem and greatly facilitated the realization of practical
spintronic devices. Here, we demonstrate a room-temperature MTJ based on
Fe3GaTe2/WS2/Fe3GaTe2 heterostructure. The tunnelling magnetoresistance (TMR)
ratio is up to 213% with high spin polarization of 72% at 10 K, the highest
ever reported in Fe3GaTe2-based MTJs up to now. The tunnelling spin-valve
signal robustly exists at room temperature (300 K) with bias current down to 10
nA. Moreover, the spin polarization can be modulated by bias current and the
TMR shows a sign reversal at large bias current. Our work sheds light on the
potential application for low-energy consumption all-2D vdW spintronics and
offers alternative routes for the electronic control of spintronic devices.

###Picosecond all-optical switching of magnetic tunnel junctions|Jun-Yang Chen,Li He,Jian-Ping Wang,Mo Li###

Picosecond all-optical switching of magnetic tunnel junctions. Control of magnetism without using magnetic fields enables large-scale
integration of spintronic devices for memory, computation and communication in
the beyond-CMOS era. Mechanisms including spin torque transfer, spin Hall
effect, and electric field or strain assisted switching have been implemented
to switch magnetization in various spintronic devices. Their operation speed,
however, is fundamentally limited by the spin precession time to be longer than
10-100 picoseconds. Overcoming such a speed constraint is critical for the
prospective development of spintronics. Here we report the demonstration of
picosecond all-optical switching of a magnetic tunnel junction (MTJ)- the
building block of spintronic logic and memory -only using single telecom-band,
infrared laser pulses. This first optically switchable MTJ uses ferrimagnetic
GdFeCo as the free layer, and its switching is directly readout by measuring
its tunneling magnetoresistance with a DR/R ratio of 0.6%. An instrument
limited switching repetition rate at MHz has been demonstrated, but the
fundamental limit should be higher than tens of GHz. This result represents an
important step toward integrated opto-spintronic devices that combines
spintronics and photonics technologies to enable ultrafast conversion between
fundamental information carriers of electron spins and photons.

###Heterogeneous Memristive Devices Enabled by Magnetic Tunnel Junction Nanopillars Surrounded by Resistive Silicon Switches|Yu Zhang,Xiaoyang Lin,Jean-Paul Adam,Guillaume Agnus,Wenlong Cai,Jean-Rene Coudevylle,Nathalie Isac,Jianlei Yang,Huaiwen Yang,Wang Kang,Kaihua Cao,Hushan Cui,Deming Zhang,Youguang Zhang,Chao Zhao,Weisheng Zhao,Dafine Ravelosona###

Heterogeneous Memristive Devices Enabled by Magnetic Tunnel Junction Nanopillars Surrounded by Resistive Silicon Switches. Emerging non-volatile memories (NVMs) have currently attracted great interest
for their potential applications in advanced low-power information storage and
processing technologies. Conventional NVMs, such as magnetic random access
memory (MRAM) and resistive random access memory (RRAM) suffer from limitations
of low tunnel magnetoresistance (TMR), low access speed or finite endurance.
NVMs with synergetic advantages are still highly desired for future computer
architectures. Here, we report a heterogeneous memristive device composed of a
magnetic tunnel junction (MTJ) nanopillar surrounded by resistive silicon
switches, named resistively enhanced MTJ (Re-MTJ), that may be utilized for
novel memristive memories, enabling new functionalities that are inaccessible
for conventional NVMs. The Re-MTJ device features a high ON/OFF ratio of >1000%
and multilevel resistance behaviour by combining magnetic switching together
with resistive switching mechanisms. The magnetic switching originates from the
MTJ, while the resistive switching is induced by a point-switching filament
process that is related to the mobile oxygen ions. Microscopic evidence of
silicon aggregated as nanocrystals along the edges of the nanopillars verifies
the synergetic mechanism of the heterogeneous memristive device. This device
may provide new possibilities for advanced memristive memory and computing
architectures, e.g., in-memory computing and neuromorphics.

###First-principles spin-transfer torque in CuMnAs$|$GaP$|$CuMnAs junctions|Maria Stamenova,Razie Mohebbi,Jamileh Seyedyazdi,Ivan Rungger,Stefano Sanvito###

First-principles spin-transfer torque in CuMnAs$|$GaP$|$CuMnAs junctions. We demonstrate that an all-antiferromagnetic tunnel junction with current
perpendicular to the plane geometry can be used as an efficient spintronics
device with potential high frequency operation. By using state-of-the-art
density functional theory combined with quantum transport, we show that the
N\'eel vector of the electrodes can be manipulated by spin-transfer torque.
This is staggered over the two different magnetic sublattices and can generate
dynamics and switching. At the same time the different magnetization states of
the junction can be read by standard tunnelling magnetoresistance. Calculations
are performed for CuMnAs$|$GaP$|$CuMnAs junctions with different surface
terminations between the anti-ferromagnetic CuMnAs electrodes and the
insulating GaP spacer. In particular we find that the torque remains staggered
regardless of the termination, while the magnetoresistance depends on the
microscopic details of the interface.

###Magnetoresistance and spin-transfer torque in magnetic tunnel junctions|J. Z. Sun,D. C. Ralph###

Magnetoresistance and spin-transfer torque in magnetic tunnel junctions. We comment on both recent progress and lingering puzzles related to research
on magnetic tunnel junctions (MTJs). MTJs are already being used in
applications such as magnetic-field sensors in the read heads of disk drives,
and they may also be the first device geometry in which spin-torque effects are
applied to manipulate magnetic dynamics, in order to make nonvolatile magnetic
random access memory. However, there remain many unanswered questions about
such basic properties as the magnetoresistance of MTJs, how their properties
change as a function of tunnel-barrier thickness and applied bias, and what are
the magnitude and direction of the spin-transfer-torque vector induced by a
tunnel current.

###Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates|Zhenchao Wen,Hiroaki Sukegawa,Shinya Kasai,Koichiro Inomata,Seiji Mitani###

Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates. We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy based
magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate.
Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a
flat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance
(TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure on
a 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switching
was achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a
switching layer. Using a thermal activation model, the intrinsic critical
current density (Jc0) was determined to be 8.2 x 10^6 A/cm^2, which is lower
than 2.9 x 10^7 A/cm^2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett.
100, 182403 (2012)]. We found that the Gilbert damping constant evaluated using
ferromagnetic resonance measurements for the polycrystalline CFA film was
~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0
for the polycrystalline MTJ was mainly attributed to the low damping of the CFA
layer compared with the value in the epitaxial one (~0.04).

###Giant Tunneling Magnetoresistance in Spin-Filter van der Waals Heterostructures|Tiancheng Song,Xinghan Cai,Matisse Wei-Yuan Tu,Xiaoou Zhang,Bevin Huang,Nathan P. Wilson,Kyle L. Seyler,Lin Zhu,Takashi Taniguchi,Kenji Watanabe,Michael A. McGuire,David H. Cobden,Di Xiao,Wang Yao,Xiaodong Xu###

Giant Tunneling Magnetoresistance in Spin-Filter van der Waals Heterostructures. Magnetic multilayer devices that exploit magnetoresistance are the backbone
of magnetic sensing and data storage technologies. Here we report novel
multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals
(vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts
as a spin-filter tunnel barrier sandwiched between graphene contacts. We
demonstrate tunneling magnetoresistance which is drastically enhanced with
increasing CrI3 layer thickness, reaching a record 19,000% for magnetic
multilayer structures using four-layer sf-MTJs at low temperatures. These
devices also show multiple resistance states as a function of magnetic field,
suggesting the potential for multi-bit functionalities using an individual vdW
sf-MTJ. Using magnetic circular dichroism measurements, we attribute these
effects to the intrinsic layer-by-layer antiferromagnetic ordering of the
atomically thin CrI3. Our work reveals the possibility to push magnetic
information storage to the atomically thin limit, and highlights CrI3 as a
superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.

###Quantum oscillation of magnetoresistance in tunneling junctions with a nonmagnetic spacer|H. Itoh,J. Inoue A. Umerski,J. Mathon###

Quantum oscillation of magnetoresistance in tunneling junctions with a nonmagnetic spacer. We make a theoretical study of the quantum oscillations of the tunneling
magnetoresistance (TMR) as a function of the spacer layer thickness. Such
oscillations were recently observed in tunneling junctions with a nonmagnetic
metallic spacer at the barrier-electrode interface. It is shown that momentum
selection due to the insulating barrier and conduction via quantum well states
in the spacer, mediated by diffusive scattering caused by disorder, are
essential features required to explain the observed period of oscillation in
the TMR ratio and its asymptotic value for thick nonmagnetic spacer.

###Demonstration of nanosecond operation in stochastic magnetic tunnel junctions|Christopher Safranski,Jan Kaiser,Philip Trouilloud,Pouya Hashemi,Guohan Hu,Jonathan Z Sun###

Demonstration of nanosecond operation in stochastic magnetic tunnel junctions. Magnetic tunnel junctions operating in the superparamagnetic regime are
promising devices in the field of probabilistic computing, which is suitable
for applications like high-dimensional optimization or sampling problems.
Further, random number generation is of interest in the field of cryptography.
For such applications, a device's uncorrelated fluctuation time-scale can
determine the effective system speed. It has been theoretically proposed that a
magnetic tunnel junction designed to have only easy-plane anisotropy provides
fluctuation rates determined by its easy-plane anisotropy field, and can
perform on nanosecond or faster time-scale as measured by its
magnetoresistance's autocorrelation in time. Here we provide experimental
evidence of nanosecond scale fluctuations in a circular shaped easy-plane
magnetic tunnel junction, consistent with finite-temperature coupled macrospin
simulation results and prior theoretical expectations. We further assess the
degree of stochasticity of such signal.

###Diode effect in magnetic tunnel junctions|F. Kanjouri,N. Ryzhanova,B. Dieny,N. Strelkov,A. Vedyaev###

Diode effect in magnetic tunnel junctions. The influence on the I-V characteristics and tunnel magnetoresistance (TMR),
of impurities embedded into the insulating barrier I separating the two
ferromagnetic electrodes F of a magnetic tunnel junction, was theoretically
investigated. When the energy of the electron's bound state at the impurity
site is close to the Fermi energy, it is shown that the current and TMR are
strongly enhanced in the vicinity of the impurity. If the position of the
impurity inside the barrier is asymmetric, e.g. closer to one of the interfaces
F/I, the I-V characteristic exhibits a quasidiode behavior. The case of a
single impurity and of a random distribution of impurities within a plane were
both studied.

###Non-equilibrium Green's function based single-band tight-binding model for Fe-MgO-Fe magnetic tunnel junction devices|Tehseen Raza,Hassan Raza###

Non-equilibrium Green's function based single-band tight-binding model for Fe-MgO-Fe magnetic tunnel junction devices. Motivated by observation of very high tunnel magnetoresistance (TMR) in
Fe-MgO-Fe magnetic tunnel junction devices, we propose a theoretical model for
these devices based on a single-band tight-binding approximation. An effort is
made to capture the band dispersions over the two dimensional transverse
Brillouin zone. In the transport direction, spin dependent Hamiltonian is
prescribed for Delta_1 and Delta_5 bands. Non-equilibrium Green's function
formalism is then used to calculate transport. Features like voltage dependence
of TMR are captured quantitatively within this simple model and the trends
match well with the ones predicted by ab-initio methods and experiments.

###Low frequency 1/f noise in doped manganite grain-boundary junctions|J. B. Philipp,L. Alff,A. Marx,R. Gross###

Low frequency 1/f noise in doped manganite grain-boundary junctions. We have performed a systematic analysis of the low frequency 1/f-noise in
single grain boundary junctions in the colossal magnetoresistance material
La_{2/3}Ca_{1/3}MnO_{3-delta}. The grain boundary junctions were formed in
epitaxial La_{2/3}Ca_{1/3}MnO_{3-delta} films deposited on SrTiO_3 bicrystal
substrates and show a large tunneling magnetoresistance of up to 300% at 4.2 K
as well as ideal, rectangular shaped resistance versus applied magnetic field
curves. Below the Curie temperature T_C the measured 1/f noise is dominated by
the grain boundary. The dependence of the noise on bias current, temperature
and applied magnetic field gives clear evidence that the large amount of low
frequency noise is caused by localized sites with fluctuating magnetic moments
in a heavily disordered grain boundary region. At 4.2 K additional temporally
unstable Lorentzian components show up in the noise spectra that are most
likely caused by fluctuating clusters of interacting magnetic moments. Noise
due to fluctuating domains in the junction electrodes is found to play no
significant role.

###Spin-orbit-torque magnetization switching of a three terminal perpendicular magnetic tunnel junction|Murat Cubukcu,Olivier Boulle,Marc Drouard,Kevin Garello,Can Onur Avci,Ioan Mihai Miron,Juergen Langer,Berthold Ocker,Pietro Gambardella,Gilles Gaudin###

Spin-orbit-torque magnetization switching of a three terminal perpendicular magnetic tunnel junction. We report on the current-induced magnetization switching of a three-terminal
perpendicular magnetic tunnel junction by spin-orbit torque and the read-out
using the tunnelling magnetoresistance (TMR) effect. The device is composed of
a perpendicular Ta/FeCoB/MgO/FeCoB stack on top of a Ta current line. The
magnetization of the bottom FeCoB layer can be switched reproducibly by the
injection of current pulses with density $5\times10^{11}$ A/m$^2$ in the Ta
layer in the presence of an in-plane bias magnetic field, leading to the
full-scale change of the TMR signal. Our work demonstrates the proof of concept
of a perpendicular spin-orbit torque magnetic memory cell.

###Enhancing Spin Transfer Torque in Magnetic Tunnel Junction Devices: Exploring the Influence of Capping Layer Materials and Thickness on Device Characteristics|Tahereh Sadat Parvini,Elvira Paz,Tim Böhnert,Alejandro Schulman,Luana Benetti,Felix Oberbauer,Jakob Walowski,Farshad Moradi,Ricardo Ferreira,Markus Münzenberg###

Enhancing Spin Transfer Torque in Magnetic Tunnel Junction Devices: Exploring the Influence of Capping Layer Materials and Thickness on Device Characteristics. We have developed and optimized two categories of spin transfer torque
magnetic tunnel junctions (STT-MTJs) that exhibit a high tunnel
magnetoresistance (TMR) ratio, low critical current, high outputpower in the
micro watt range, and auto-oscillation behavior. These characteristics
demonstrate the potential of STT-MTJs for low-power, high-speed, and reliable
spintronic applications, including magnetic memory, logic, and signal
processing. The only distinguishing factor between the two categories, denoted
as A-MTJs and B-MTJs, is the composition of their free layers, 2 CoFeB/0.21
Ta/6 CoFeSiB for A-MTJs and 2 CoFeB/0.21 Ta/7 NiFe for B-MTJs. Our study
reveals that B-MTJs exhibit lower critical currents for auto-oscillation than
A-MTJs. We found that both stacks have comparable saturation magnetization and
anisotropy field, suggesting that the difference in auto-oscillation behavior
is due to the higher damping of A-MTJs compared to B-MTJs. To verify this
hypothesis, we employed the all-optical time-resolved magneto-optical Kerr
effect (TRMOKE) technique, which confirmed that STT-MTJs with lower damping
exhibited auto-oscillation at lower critical current values. Additionally, our
study aimed to optimize the STT-MTJ performance by investigating the impact of
the capping layer on the device's response to electronic and optical stimuli.

###Spin-polarized Tunneling in Hybrid Metal-Semiconductor Magnetic Tunnel Junctions|S. H. Chun,S. J. Potashnik,K. C. Ku,P. Schiffer,N. Samarth###

Spin-polarized Tunneling in Hybrid Metal-Semiconductor Magnetic Tunnel Junctions. We demonstrate efficient spin-polarized tunneling between a ferromagnetic
metal and a ferromagnetic semiconductor with highly mismatched conductivities.
This is indicated by a large tunneling magnetoresistance (up to 30%) at low
temperatures in epitaxial magnetic tunnel junctions composed of a ferromagnetic
metal (MnAs) and a ferromagnetic semiconductor (GaMnAs) separated by a
nonmagnetic semiconductor (AlAs). Analysis of the current-voltage
characteristics yields detailed information about the asymmetric tunnel
barrier. The low temperature conductance-voltage characteristics show a zero
bias anomaly and a V^1/2 dependence of the conductance, indicating a
correlation gap in the density of states of GaMnAs. These experiments suggest
that MnAs/AlAs heterostructures offer well characterized tunnel junctions for
high efficiency spin injection into GaAs.

###Universal angular magnetoresistance and spin torque in ferromagnetic/normal metal hybrids|Gerrit E. W. Bauer,Yaroslav Tserkovnyak,Daniel Huertas-Hernando,Arne Brataas###

Universal angular magnetoresistance and spin torque in ferromagnetic/normal metal hybrids. The electrical resistance of ferromagnetic/normal-metal (F/N)
heterostructures depends on the nature of the junctions which may be tunnel
barriers, point contacts, or intermetallic interfaces. For all junction types,
the resistance of disordered F/N/F perpendicular spin valves as a function of
the angle between magnetization vectors is shown to obey a simple universal
law. The spin-current induced magnetization torque can be measured by the
angular magnetoresistance of these spin valves. The results are generalized to
arbitrary magnetoelectronic circuits.

###Orange Peel coupling in granular ferromagnetic films|D. Barness,A. Frydman###

Orange Peel coupling in granular ferromagnetic films. We present magnetoresistance (MR) measurements performed on magnetic tunnel
junctions in which one of the electrodes is a granular ferromagnetic film.
These junctions exhibit a zero field resistance dip. The dip magnitude depends
on the size of the grains. We interpret these results as a consequence of the
orange peel effect between the continuous ferromagnetic film and the magnetic
grains. The coupling is found to be much stronger than that between continuous
ferromagnetic layers.

###Anomalous tunnel magnetoresistance and spin transfer torque in magnetic tunnel junctions with embedded nanoparticles|Arthur Useinov,Lin-Xiu Ye,Niazbeck Useinov,Te-Ho Wu,Chih-Huang Lai###

Anomalous tunnel magnetoresistance and spin transfer torque in magnetic tunnel junctions with embedded nanoparticles. The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with
embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic
model. The simulation was performed for electron tunneling through the
insulating layer with embedded magnetic and nonmagnetic NPs within the approach
of the double barrier subsystem connected in parallel to the single barrier
one. This model can be applied for both MTJs with in-plane magnetization and
perpendicular one. We also calculated the in-plane component of the spin
transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and
determined that its value can be much larger than in single barrier system
(SBS) for the same tunneling thickness. The reported simulation reproduces
experimental data of the TMR suppression and peak-like TMR anomalies at low
voltages available in literature.

###Mesoscopic Tunneling Magnetoresistance|Gonzalo Usaj,Harold. U. Baranger###

Mesoscopic Tunneling Magnetoresistance. We study spin-dependent transport through
ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic
Coulomb blockade regime. A general transport equation allows us to calculate
the conductance in the absence or presence of spin-orbit interaction and for
arbitrary orientation of the lead magnetizations. The tunneling
magnetoresistance (TMR), defined at the Coulomb blockade conductance peaks, is
calculated and its probability distribution presented. We show that mesoscopic
fluctuations can lead to the optimal value of the TMR.

###Influence of Roughness and Disorder on Tunneling Magnetoresistance|P. X. Xu,V. M. Karpan,K. Xia,M. Zwierzycki,I. Marushchenko,P. J. Kelly###

Influence of Roughness and Disorder on Tunneling Magnetoresistance. A systematic, quantitative study of the effect of interface roughness and
disorder on the magnetoresistance of FeCo$|$vacuum$|$FeCo magnetic tunnel
junctions is presented based upon parameter-free electronic structure
calculations. Surface roughness is found to have a very strong effect on the
spin-polarized transport while that of disorder in the leads (leads consisting
of a substitutional alloy) is weaker but still sufficient to suppress the huge
tunneling magneto-resistance (TMR) predicted for ideal systems.

###Tunneling anisotropic magnetoresistance in single-molecule magnet junctions|Haiqing Xie,Qiang Wang,Hujun Jiao,J. -Q. Liang###

Tunneling anisotropic magnetoresistance in single-molecule magnet junctions. We theoretically investigate quantum transport through single-molecule magnet
(SMM) junctions with ferromagnetic and normal-metal leads in the sequential
regime. The current obtained by means of the rate-equation gives rise to the
tunneling anisotropic magnetoresistance (TAMR), which varies with the angle
between the magnetization direction of ferromagnetic lead and the easy axis of
SMM. The angular dependence of TAMR can serve as a probe to determine
experimentally the easy axis of SMM. Moreover, it is demonstrated that both the
magnitude and sign of TAMR are tunable by the bias voltage, suggesting a
promising TAMR based spintronic molecule-device.

###Local Tunneling Magnetoresistance probed by Low-Temperature Scanning Laser Microscopy|Robert Werner,Mathias Weiler,Aleksandr Yu. Petrov,Bruce A. Davidson,Rudolf Gross,Reinhold Kleiner,Sebastian T. B. Goennenwein,Dieter Koelle###

Local Tunneling Magnetoresistance probed by Low-Temperature Scanning Laser Microscopy. Tunneling magnetoresistance (TMR) in a vertical manganite junction was
investigated by low-temperature scanning laser microscopy (LTSLM) allowing to
determine the local relative magnetization M orientation of the two electrodes
as a function of magnitude and orientation of the external magnetic field H.
Sweeping the field amplitude at fixed orientation revealed magnetic domain
nucleation and propagation in the junction electrodes. For the high-resistance
state an almost single-domain antiparallel magnetization configuration was
achieved, while in the low-resistance state the junction remained in a
multidomain state. Calculated resistance $R_\mathrm{calc}(H)$ based on the
local M configuration obtained by LTSLM is in quantitative agreement with R(H)
measured by magnetotransport.

###Bias voltage effects on tunneling magnetoresistance in Fe/MgAl${}_2$O${}_4$/Fe(001) junctions: Comparative study with Fe/MgO/Fe(001) junctions|Keisuke Masuda,Yoshio Miura###

Bias voltage effects on tunneling magnetoresistance in Fe/MgAl${}_2$O${}_4$/Fe(001) junctions: Comparative study with Fe/MgO/Fe(001) junctions. We investigate bias voltage effects on the spin-dependent transport
properties of Fe/MgAl${}_2$O${}_4$/Fe(001) magnetic tunneling junctions (MTJs)
by comparing them with those of Fe/MgO/Fe(001) MTJs. By means of the
nonequilibrium Green's function method and the density functional theory, we
calculate bias voltage dependences of magnetoresistance (MR) ratios in both the
MTJs. We find that in both the MTJs, the MR ratio decreases as the bias voltage
increases and finally vanishes at a critical bias voltage $V_{\rm c}$. We also
find that the critical bias voltage $V_{\rm c}$ of the MgAl${}_2$O${}_4$-based
MTJ is clearly larger than that of the MgO-based MTJ. Since the in-plane
lattice constant of the Fe/MgAl${}_2$O${}_4$/Fe(001) supercell is twice that of
the Fe/MgO/Fe(001) one, the Fe electrodes in the MgAl${}_2$O${}_4$-based MTJs
have an identical band structure to that obtained by folding the Fe band
structure of the MgO-based MTJs in the Brillouin zone of the in-plane wave
vector. We show that such a difference in the Fe band structure is the origin
of the difference in the critical bias voltage $V_{\rm c}$ between the
MgAl${}_2$O${}_4$- and MgO-based MTJs.

###Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy|Robert Werner,Alexandr Yu. Petrov,Lucero Alvarez Mino,Reinhold Kleiner,Dieter Koelle,Bruce A. Davidson###

Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy. We report resistance versus magnetic field measurements for a
La0.65Sr0.35MnO3/SrTiO3/La0.65Sr0.35MnO3 tunnel junction grown by
molecular-beam epitaxy, that show a large field window of extremely high
tunneling magnetoresistance (TMR) at low temperature. Scanning the in-plane
applied field orientation through 360^/circ, the TMR shows 4-fold symmetry,
i.e. biaxial anisotropy, aligned with the crystalline axes but not the junction
geometrical long axis. The TMR reaches ~ 1900% at 4K, corresponding to an
interfacial spin polarization of > 95% assuming identical interfaces. These
results show that uniaxial anisotropy is not necessary for large TMR, and lay
the groundwork for future improvements in TMR in manganite junctions.

###Tunnel magnetoresistance in double spin filter junctions|Alireza Saffarzadeh###

Tunnel magnetoresistance in double spin filter junctions. We consider a new type of magnetic tunnel junction, which consists of two
ferromagnetic tunnel barriers acting as spin filters (SFs), separated by a
nonmagnetic metal (NM) layer. Using the transfer matrix method and the
free-electron approximation, the dependence of the tunnel magnetoresistance
(TMR) on the thickness of the central NM layer, bias voltage and temperature in
the double SF junction are studied theoretically. It is shown that the TMR and
electron-spin polarization in this structure can reach very large values under
suitable conditions. The highest value of the TMR can reach 99%. By an
appropriate choice of the thickness of the central NM layer, the degree of spin
polarization in this structure will be higher than that of the single SF
junctions. These results may be useful in designing future spin-polarized
tunnelling devices.

###Proposal of Analog In-Memory Computing with Magnified Tunnel Magnetoresistance Ratio and Universal STT-MRAM Cell|Hao Cai,Yanan Guo,Bo Liu,Mingyang Zhou,Juntong Chen,Xinning Liu,Jun Yang###

Proposal of Analog In-Memory Computing with Magnified Tunnel Magnetoresistance Ratio and Universal STT-MRAM Cell. In-memory computing (IMC) is an effectual solution for energy-efficient
artificial intelligence applications. Analog IMC amortizes the power
consumption of multiple sensing amplifiers with analog-to-digital converter
(ADC), and simultaneously completes the calculation of multi-line data with
high parallelism degree. Based on a universal one-transistor one-magnetic
tunnel junction (MTJ) spin transfer torque magnetic RAM (STT-MRAM) cell, this
paper demonstrates a novel tunneling magnetoresistance (TMR) ratio magnifying
method to realize analog IMC. Previous concerns include low TMR ratio and
analog calculation nonlinearity are addressed using device-circuit interaction.
Peripheral circuits are minimally modified to enable in-memory matrix-vector
multiplication. A current mirror with feedback structure is implemented to
enhance analog computing linearity and calculation accuracy. The proposed
design maximumly supports 1024 2-bit input and 1-bit weight
multiply-and-accumulate (MAC) computations simultaneously. The 2-bit input is
represented by the width of the input (IN) pulses, while the 1-bit weight is
stored in STT-MRAM and the x7500 magnified TMR (m-TMR) ratio is obtained by
latching. The proposal is simulated using 28-nm CMOS process and MTJ compact
model. The integral nonlinearity is reduced by 57.6% compared with the
conventional structure. 9.47-25.4 TOPS/W is realized with 2-bit input, 1-bit
weight and 4-bit output convolution neural network (CNN).

###RF amplification property of the MgO-based magnetic tunnel junction using field-induced ferromagnetic resonance|K. Konishi,D. K. Dixit,A. A. Tulapurkar,S. Miwa,T. Nozaki,H. Kubota,A. Fukushima,S. Yuasa,Y. Suzuki###

RF amplification property of the MgO-based magnetic tunnel junction using field-induced ferromagnetic resonance. The radio-frequency (RF) voltage amplification property of a tunnel
magnetoresistance device driven by an RF external-magnetic-field-induced
ferromagnetic resonance was studied. The proposed device consists of a magnetic
tunnel junction (MTJ) and an electrically isolated coplanar waveguide. The
input RF voltage applied to the waveguide can excite the resonant dynamics in
the free layer magnetization, leading to the generation of an output RF voltage
under a DC bias current. The dependences of the RF voltage gain on the static
external magnetic field strength and angle were systematically investigated.
The design principles for the enhancement of the gain factor are also
discussed.

###Interface-driven giant tunnel magnetoresistance in (111)-oriented junctions|Keisuke Masuda,Hiroyoshi Itoh,Yoshio Miura###

Interface-driven giant tunnel magnetoresistance in (111)-oriented junctions. We theoretically study the tunnel magnetoresistance (TMR) effect in
(111)-oriented junctions Co/MgO/Co(111) and Ni/MgO/Ni(111). The Co-based
junction is shown to have a TMR ratio over 2000$\%$, which is one order higher
than that of the Ni-based one. The high TMR ratio is attributed to the
interfacial resonance effect: The interfacial $d$-$p$ antibonding states are
formed close to the Fermi level in the majority-spin channel and these states
in both interfaces resonate with each other. This differs essentially from the
conventional coherent tunneling mechanism of high TMR ratios in
Fe(Co)/MgO/Fe(Co)(001).

###Spin-polarized tunneling spectroscopy in tunnel junctions with half-metallic electrodes|M. Bowen,A. Barthélémy,M. Bibes,E. Jacquet,J. -P. Contour,A. Fert,F. Ciccacci,L. Dùo,R. Bertacco###

Spin-polarized tunneling spectroscopy in tunnel junctions with half-metallic electrodes. We have studied the magnetoresistance (TMR) of tunnel junctions with
electrodes of La2/3Sr1/3MnO3 and we show how the variation of the conductance
and TMR with the bias voltage can be exploited to obtain a precise information
on the spin and energy dependence of the density of states. Our analysis leads
to a quantitative description of the band structure of La2/3Sr1/3MnO3 and
allows the determination of the gap delta between the Fermi level and the
bottom of the t2g minority spin band, in good agreement with data from
spin-polarized inverse photoemission experiments. This shows the potential of
magnetic tunnel junctions with half-metallic electrodes for spin-resolved
spectroscopic studies.

###IrCrMnZ (Z=Al, Ga, Si, Ge) Heusler alloys as electrode materials for MgO-based magnetic tunneling junctions: A first-principles study|Tufan Roy,Masahito Tsujikawa,Masafumi Shirai###

IrCrMnZ (Z=Al, Ga, Si, Ge) Heusler alloys as electrode materials for MgO-based magnetic tunneling junctions: A first-principles study. We study IrCrMnZ (Z=Al, Ga, Si, Ge) systems using first-principles
calculations from the perspective of their application as the electrode
materials of MgO-based MTJs. These materials have highly spin-polarized
conduction electrons with partially occupied $\Delta_1$ band, which is
important for coherent tunneling in parallel magnetization configuration. The
Curie temperatures of IrCrMnAl and IrCrMnGa are very high (above 1300 K) as
predicted from mean-field-approximation. The stability of ordered phase against
various antisite disorders has been investigated. We discuss here the effect of
"spin-orbit-coupling" on the electronic structure around Fermi level. Further,
we investigate the electronic structure of IrCrMnZ/MgO heterojunction along
(001) direction. IrCrMnAl/MgO and IrCrMnGa/MgO maintain half-metallicity even
at the MgO interface, with no interfacial states at/around Fermi level in the
minority-spin channel. Large majority-spin conductance of IrCrMnAl/MgO/IrCrMnAl
and IrCrMnGa/MgO/IrCrMnGa is reported from the calculation of ballistic
spin-transport property for parallel magnetization configuration. We propose
IrCrMnAl/MgO/IrCrMnAl and IrCrMnGa/MgO/IrCrMnGa as promising MTJs with a weaker
temperature dependence of tunneling magnetoresistance ratio, owing to their
very high Curie temperatures.

###Giant tunnel magnetoresistance with a single magnetic phase-transition electrode|Jia Zhang,X. Z. Chen,C. Song,J. F. Feng,H. X. Wei,Jing-Tao Lü###

Giant tunnel magnetoresistance with a single magnetic phase-transition electrode. Magnetic phase transition tunnel magnetoresistance (MPT-TMR) effect with a
single magnetic electrode has been investigated by first-principles
calculations. The calculations show that the MPT-TMR of FeRh/MgO/Cu tunnel
junction can be as high as hundreds of percent when the magnetic structure of
FeRh changes from G-type antiferromagnetic (GAFM) to ferromagnetic order. This
new type of MPT-TMR may be superior to the tunnel anisotropic magnetoresistance
because of its huge magneto-resistance effect and similar structural
simplicity. The main mechanism for the giant MPT-TMR can be attributed to the
formation of interface resonant states at GAFM-FeRh/MgO interface. A direct
FeRh/MgO interface is found to be necessary for achieving high MPT-TMR
experimentally. Moreover, we find the FeRh/MgO interface with FeRh in
ferromagnetic phase has nearly full spin-polarization due to the negligible
majority transmission and significantly different Fermi surface of two spin
channels. Thus, it may act as a highly efficient and tunable spin-injector. In
addition, electric field driven MPT of FeRh-based hetero-magnetic
nanostructures can be utilized to design various energy efficient tunnel
junction structures and the corresponding lower power consumption devices. Our
results will stimulate further experimental investigations of MPT-TMR and other
fascinating phenomenon of FeRh-based tunnel junctions that may be promising in
antiferromagnetic spintronics.

###Fe- and Co-based magnetic tunnel junctions with AlN and ZnO spacers|Gokaran Shukla,Stefano Sanvito,Geunsik Lee###

Fe- and Co-based magnetic tunnel junctions with AlN and ZnO spacers. AlN and ZnO, two wide band-gap semiconductors extensively used in the display
industry, crystallise in the wurtzite structure, which can favour the formation
of epitaxial interfaces to close-packed common ferromagnets. Here we explore
these semiconductors as material for insulating barriers in magnetic tunnel
junctions. In particular, the {\it ab initio} quantum transport code {\it
Smeagol} is used to model the $X$[111]/$Y$[0001]/$X$[111] ($X=$ Co and Fe, $Y=$
AlN and ZnO) family of junctions. Both semiconductors display a valance-band
top with $p$-orbital character, while the conduction band bottom exhibits
$s$-type symmetry. The smallest complex-band decay coefficient in the forbidden
energy-gap along the [0001] direction is associated with the $\Delta_1$
symmetry, and connects across the band gap at the $\Gamma$ point in 2D
Brillouin zones. This feature enables spin filtering and may result in a large
tunnelling magnetoresistance. In general, we find that Co-based junctions
present limited spin filtering and little magnetoresistance at low bias, since
both spin sub-bands cross the Fermi level with $\Delta_1$ symmetry. This
contrasts the situation of Fe, where only the minority $\Delta_1$ band is
available. However, even in the case of Fe the magnitude of the
magnetoresistance at low bias remains relatively small, mostly due to
conduction away from the $\Gamma$ point and through complex bands with symmetry
different than $\Delta_1$. The only exception is for the Fe/AlN/Fe junction,
where we predict a magnetoresitance of around 1,000\% at low bias.

###Half-metallic magnetism and the search for better spin valves|Karin Everschor-Sitte,Matthias Sitte,Allan H. MacDonald###

Half-metallic magnetism and the search for better spin valves. We use a previously proposed theory for the temperature dependence of
tunneling magnetoresistance to shed light on ongoing efforts to optimize spin
valves. First we show that a mechanism in which spin valve performance at
finite temperatures is limited by uncorrelated thermal fluctuations of
magnetization orientations on opposite sides of a tunnel junction is in good
agreement with recent studies of the temperature-dependent magnetoresistance of
high quality tunnel junctions with MgO barriers. Using this insight, we propose
a simple formula which captures the advantages for spin-valve optimization of
using materials with a high spin polarization of Fermi-level tunneling
electrons, and of using materials with high ferromagnetic transition
temperatures. We conclude that half-metallic ferromagnets can yield better
spin-value performance than current elemental transition metal ferromagnet/MgO
systems only if their ferromagnetic transition temperatures exceed $\sim
950~\mathrm{K}$.

###Interfacial Effects of Al-Termination on Spin Transport in Magnetic Tunnel Junctions|T. Tzen Ong,A. M. Black-Schaffer,W. Shen,B. A. Jones###

Interfacial Effects of Al-Termination on Spin Transport in Magnetic Tunnel Junctions. Experiments have shown that the tunneling current in a Co/Al$_2$O$_3$
magnetic tunneling junction (MTJ) is positively spin polarized, opposite to
what is intuitively expected from standard tunneling theory which gives the
spin polarization as exclusively dependent on the density of states (DOS) at
$E_F$ of the Co layers. Here we report theoretical results that give a positive
tunneling spin polarization and tunneling magnetoresistance (TMR) that is in
good agreement with experiments. From density functional theory (DFT)
calculations, an Al-rich interface MTJ with atomic-level disorder is shown to
have a positively polarized DOS near the interface. We also provide an atomic
model calculation which gives insights into the source of the positive
polarization. A layer and spin dependent effective mass model, using values
extracted from the DFT results, is then used to calculate the tunneling
current, which shows positive spin polarization. Finally, we calculate the TMR
from the tunneling spin polarization which shows good agreement with
experiments.

###Impurity-induced tuning of quantum well states in spin-dependent resonant tunneling|A. Kalitsov,A. Coho,N. Kioussis,A. Vedyayev,M. Chshiev,A. Granovsky###

Impurity-induced tuning of quantum well states in spin-dependent resonant tunneling. We report exact model calculations of the spin-dependent tunneling in double
magnetic tunnel junctions in the presence of impurities in the well. We show
that the impurity can tune selectively the spin channels giving rise to a wide
variety of interesting and novel transport phenomena. The tunneling
magnetoresistance, the spin polarization and the local current can be
dramatically enhanced or suppressed by impurities. The underlying mechanism is
the impurity-induced shift of the quantum well states (QWS) which depends on
the impurity potential, impurity position and the symmetry of the QWS.

###Quantum Transport with Spin Dephasing: A Nonequilibrium Green's Function Approach|Ahmet Ali Yanik,Gerhard Klimeck,Supriyo Datta###

Quantum Transport with Spin Dephasing: A Nonequilibrium Green's Function Approach. A quantum transport model incorporating spin scattering processes is
presented using the non-equilibrium Green's function (NEGF) formalism within
the self-consistent Born approximation. This model offers a unified approach by
capturing the spin-flip scattering and the quantum effects simultaneously. A
numerical implementation of the model is illustrated for magnetic tunnel
junction devices with embedded magnetic impurity layers. The results are
compared with experimental data, revealing the underlying physics of the
coherent and incoherent transport regimes. It is shown that small variations in
magnetic impurity spin-states/concentrations could cause large deviations in
junction magnetoresistances.

###Low-frequency noise and tunnelling magnetoresistance in Fe(110)/MgO(111)/Fe(110) epitaxial magnetic tunnel junctions|R. Guerrero,F. G. Aliev,R. Villar,J. Hauch,M. Fraune,G. Guntherodt,K. Rott,H. Bruckl,G. Reiss###

Low-frequency noise and tunnelling magnetoresistance in Fe(110)/MgO(111)/Fe(110) epitaxial magnetic tunnel junctions. We report on tunnelling magnetoresistance (TMR), current-voltage (IV)
characteristics and low frequency noise in epitaxially grown
Fe(110)/MgO(111)/Fe(110) magnetic tunnel junctions (MTJs) with dimensions from
2x2 to 20x20 um2. The evaluated MgO energy barrier (0.50+/-0.08 eV), the
barrier width (13.1+/-0.5 angstrom) as well as the resistance times area
product (7+/-1 Mohmsum2) show relatively small variation, confirming a high
quality epitaxy and uniformity of all MTJs studied. The noise power, though
exhibiting large variation, was observed to be roughly anticorrelated with the
TMR. Surprisingly, for the largest junctions we observed a strong enhancement
of the normalized low-frequency noise in the antiparallel magnetic
configuration. This behaviour could be related to an interplay between the
magnetic state and the local barrier defects structure of the epitaxial MTJs

###Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOx barriers|T. Newhouse-Illige,Y. H. Xu,Y. H. Liu,S. Huang,H. Kato,C. Bi,M. Xu,B. J. LeRoy,W. G. Wang###

Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOx barriers. Perpendicular magnetic tunnel junctions with GdOX tunneling barriers have
shown a unique voltage controllable interlayer magnetic coupling effect. Here
we investigate the quality of the GdOX barrier and the coupling mechanism in
these junctions by examining the temperature dependence of the tunneling
magnetoresistance and the interlayer coupling from room temperature down to 11
K. The barrier is shown to be of good quality with the spin independent
conductance only contributing a small portion, 14%, to the total room
temperature conductance, similar to AlOX and MgO barriers. The interlayer
coupling, however, shows an anomalously strong temperature dependence including
sign changes below 80 K. This non-trivial temperature dependence is not
described by previous models of interlayer coupling and may be due to the large
induced magnetic moment of the Gd ions in the barrier.

###Tunneling magnetoresistance in Mn$_2$Au-based pure antiferromagnetic tunnel junction|Xingtao Jia,Hui-Min Tang,Shi-Zhuo Wan###

Tunneling magnetoresistance in Mn$_2$Au-based pure antiferromagnetic tunnel junction. Antiferromagnetic (AF) spintronics is merit on ultra-high operator speed and
stability in the presence of magnetic field. To fully use the merit, the device
should be pure rather than hybrid with ferromagnet or ferrimagnet. For the
magnetism in the antiferromagnet is canceled by that of different sublattices,
breaking the symmetry in the material can revive the native magnetism, which
can be detected by the magnetoresistance (MR) effect. Achieving noticeable MR
effect in the pure AF device is diffcult but essential for the AF spintronic
applications. Here, we study the tunnel magnetoresistance(TMR) effect in the
Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb pure AF magnetic tunnel junctions (AF-MTJs) based
on a first-principle scattering theory. Giant TMRs with order of 1000% are
predicted in some symmetric junctions, which is originated from the interfacial
resonance tunneling effect related with the k dependent complex band structures
of CdO and Mn$_2$Au in companion with the enhanced spin polarization of the
interfacial magnetic atoms. The effect of voltage bias and interfacial disorder
such as Oxygen vacancy, Manganese vacancy, and Manganese-Cadmium exchanges at
Mn2Au/CdO interfaces are studied also. Our studies suggest
Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb AFMTJs promising material for AF spintronic
application, and rocksalt CdO a potential symmetry filtering material for
spintronic applications.

###Superconducting triplet pairings and anisotropic magnetoresistance effects in ferromagnet/superconductor/ferromagnet double-barrier junctions|Andreas Costa,Jaroslav Fabian###

Superconducting triplet pairings and anisotropic magnetoresistance effects in ferromagnet/superconductor/ferromagnet double-barrier junctions. Ferromagnetic spin valves offer the key building blocks to integrate giant-
and tunneling-magnetoresistance effects into spintronics devices. Starting from
a generalized Blonder-Tinkham-Klapwijk approach, we theoretically investigate
the impact of interfacial Rashba and Dresselhaus spin-orbit couplings on the
tunneling conductance, and thereby the magnetoresistance characteristics, of
ferromagnet/superconductor/ferromagnet spin-valve junctions embedding thin
superconducting spacers between the either parallel or antiparallel magnetized
ferromagnets. We focus on the unique interplay between usual electron
tunnelings-that fully determine the magnetoresistance in the normal-conducting
state-and the peculiar Andreev reflections in the superconducting state. In the
presence of interfacial spin-orbit couplings, special attention needs to be
paid to the spin-flip ("unconventional") Andreev-reflection process that is
expected to induce superconducting triplet correlations in proximitized
regions. As a transport signature of these triplet pairings, we detect
conductance double peaks around the singlet-gap energy, reflecting the
competition between the singlet and an additionally emerging triplet gap; the
latter is an effective superconducting gap that can be ascribed to the
formation of triplet Cooper pairs through interfacial spin-flip scatterings
(i.e., to the generation of an effective triplet-pairing term in the order
parameter). We thoroughly analyze the Andreev reflections' role in connection
with superconducting magnetoresistance phenomena, and eventually unravel huge
conductance and magnetoresistance magnetoanisotropies-easily exceeding their
normal-state counterparts by several orders of magnitude-as another
experimentally accessible fingerprint of unconventional Andreev reflections.

###Resonant TMR inversion in LiF/EuS based spin-filter tunnel junctions|Fen Liu,Yihang Yang,Qian Xue,Zhiwei Gao,Aixi Chen,Guo-Xing Miao###

Resonant TMR inversion in LiF/EuS based spin-filter tunnel junctions. Resonant tunneling can lead to inverse tunnel magnetoresistance when impurity
levels rather than direct tunneling dominate the transport process. We
fabricated hybrid magnetic tunnel junctions of CoFe/LiF/EuS/Ti, with an
epitaxial LiF energy barrier joined with a polycrystalline EuS spin-filter
bar-rier. Due to the water solubility of LiF, the devices were fully packaged
in situ. The devices showed sizeable positive TMR up to 16% at low bias
voltages but clearly inverted TMR at higher bias voltages. The TMR inversion
depends sensitively on the thickness of LiF, and the tendency of inversion
disap-pears when LiF gets thick enough and recovers its intrinsic properties.

###Negative tunneling magnetoresistance by canted magnetization in MgO/NiO tunnel barriers|Hyunsoo Yang,See-Hun Yang,Dong-Chen Qi,Andrivo Rusydi,Hiroyo Kawai,Mark Saeys,Titus Leo,David J. Smith,Stuart S. P. Parkin###

Negative tunneling magnetoresistance by canted magnetization in MgO/NiO tunnel barriers. The influence of insertion of an ultra-thin NiO layer between the MgO barrier
and ferromagnetic electrode in magnetic tunnel junctions has been investigated
by measuring the tunneling magnetoresistance and the X-ray magnetic circular
dichroism (XMCD). The magnetoresistance shows a high asymmetry with respect to
bias voltage, giving rise to a negative value of -16% at 2.8 K. We attribute
this to the formation of non-collinear spin structures in the NiO layer as
observed by XMCD. The magnetic moments of the interface Ni atoms tilt from the
easy axis due to exchange interaction and the tilting angle decreases with
increasing the NiO thickness. The experimental observations are further support
by non-collinear spin density functional theory.

###Strongly suppressed 1/f noise and enhanced magnetoresistance in epitaxial Fe-V/MgO/Fe magnetic tunnel junctions|D. Herranz,F. Bonell,A. Gomez-Ibarlucea,S. Andrieu,F. Montaigne,R. Villar1,C. Tiusan,F. G. Aliev###

Strongly suppressed 1/f noise and enhanced magnetoresistance in epitaxial Fe-V/MgO/Fe magnetic tunnel junctions. Alloying Fe electrodes with V, through reduced FeV/MgO interface mismatch in
epitaxial magnetic tunnel junctions with MgO barriers, notably suppresses both
nonmagnetic (parallel) and magnetic (antiparallel) state 1/f noise and enhances
tunnelling magnetoresistance (TMR). A comparative study of the room temperature
electron transport and low frequency noise in Fe1-xVx/MgO/Fe and Fe/MgO/Fe1-xVx
MTJs with 0 <= x <= 0.25 reveals that V doping of the bottom electrode for x <
0.1 reduces in nearly 2 orders of magnitude the normalized nonmagnetic and
magnetic 1/f noise. We attribute the enhanced TMR and suppressed 1/f noise to
strongly reduced misfit and dislocation density.

###Magnetic Tunnel Junction Performance Under Mechanical Strain|Niklas Roschewsky,Sebastian Schafer,Frances Hellman,Vladimir Nikitin###

Magnetic Tunnel Junction Performance Under Mechanical Strain. In this work we investigate the effect of the mechanical stress on the
performance of magnetic tunnel junctions (MTJ) with perpendicular magnetic
anisotropy. We developed a 4-point bending setup, that allows us to apply a
constant stress over a large substrate area with access to electrical
measurements and external magnetic field. This setup enables us to measure key
device performance parameters, such as tunnel magnetoresistance (TMR),
switching current ($I_c^{50\%}$) and thermal stability ($\Delta$), as a
function of applied stress. We find that variations in these parameters are
negligible: less than $\SI{2}{\percent}$ over the entire measured range between
the zero stress condition and the maximum stress at the point of wafer
breakage.

###Voltage-controlled antiferromagnetism in magnetic tunnel junctions|Meng Xu,Mingen Li,Pravin Khanal,Ali Habiboglu,Blake Insana,Yuzan Xiong,Thomas Peterson,Jason C. Myers,Deborah Ortega,Hongwei Qu,C. L. Chien,Wei Zhang,Jian-Ping Wang,W. G. Wang###

Voltage-controlled antiferromagnetism in magnetic tunnel junctions. We demonstrate a voltage-controlled exchange bias effect in CoFeB/MgO/CoFeB
magnetic tunnel junctions that is related to the interfacial Fe(Co)Ox formed
between the CoFeB electrodes and the MgO barrier. The unique combination of
interfacial antiferromagnetism, giant tunneling magnetoresistance, and sharp
switching of the perpendicularly-magnetized CoFeB allows sensitive detection of
the exchange bias. It is found that the exchange bias field can be isothermally
controlled by magnetic fields at low temperatures. More importantly, the
exchange bias can also be effectively manipulated by the electric field applied
to the MgO barrier due to the voltage-controlled antiferromagnetic anisotropy
in this system.

###Role of quantum confinement and interlayer coupling in CrI$_3$-graphene magnetic tunnel junctions|Jonathan J. Heath,Marcio Costa,Marco Buongiorno-Nardelli,Marcelo A. Kuroda###

Role of quantum confinement and interlayer coupling in CrI$_3$-graphene magnetic tunnel junctions. Recent demonstrations of magnetic ordering and spin transport in
two-dimensional heterostructures have opened research venues in these material
systems. In order to control and enhance the related physical phenomena,
quantitative descriptions linking experimental observations to atomic details
must be produced. Here we combine first principles and quantum ballistic
transport calculations to shed important insights from an atomistic viewpoint
on the underlying mechanisms governing spin transport in graphene/CrI$_3$
junctions. Descriptions of the electronic structure reveal that tunneling is
the dominant transport mechanism in these heterostructures and help
differentiate intermediate metamagnetic states present in the switching
process. We find that quantum confinement and layer-layer interactions are key
to describing transport in these two-dimensional systems. Ballistic transport
calculations further support these findings and yield magnetoresistance values
in remarkable agreement with experiments. The short width of these barriers
limits analysis solely based on the bulk complex band structure often employed
in the description of magnetic tunnel junctions. Our work devises mechanisms to
attain larger tunneling magnetoresistances, proving valuable to the advancement
of spin valves in layered heterostructures.

###Room temperature tunneling magnetoresistance in magnetite based junctions: Influence of tunneling barrier|D. Reisinger,P. Majewski,M. Opel,L. Alff,R. Gross###

Room temperature tunneling magnetoresistance in magnetite based junctions: Influence of tunneling barrier. Magnetite (Fe3O4) based tunnel junctions with turret/mesa structure have been
investigated for different barrier materials (SrTiO3, NdGaO3, MgO, SiO2, and
Al2O(3-x)). Junctions with a Ni counter electrode and an aluminium oxide
barrier showed reproducibly a tunneling magnetoresistance (TMR) effect at room
temperature of up to 5% with almost ideal switching behavior. This number only
partially reflects the intrinsic high spin polarization of Fe3O4. It is
considerably decreased due to an additional series resistance within the
junction. Only SiO2 and Al2O(3-x) barriers provide magnetically decoupled
electrodes as necessary for sharp switching. The observed decrease of the TMR
effect as a function of increasing temperature is due to a decrease in spin
polarization and an increase in spin-scattering in the barrier. Among the oxide
half-metals magnetite has the potential to enhance the performance of TMR based
devices.

###Enhanced tunneling magnetoresistance in Fe|ZnSe double junctions|Jeronimo Peralta Ramos,Ana Maria Llois###

Enhanced tunneling magnetoresistance in Fe|ZnSe double junctions. We calculate the tunneling magnetoresistance (TMR) of Fe|ZnSe|Fe|ZnSe|Fe
(001) double magnetic tunnel junctions as a function of the in-between Fe
layer's thickness, and compare these results with those of Fe|ZnSe|Fe simple
junctions. The electronic band structures are modeled by a parametrized
tight-binding Hamiltonian fitted to ab initio calculations, and the conductance
is calculated within the Landauer formalism expressed in terms of Green's
functions. We find that the conductances for each spin channel and the TMR
strongly depend on the in-between Fe layer's thickness, and that in some cases
they are enhanced with respect to simple junctions, in qualitative agreement
with recent experimental studies performed on similar systems. By using a 2D
double junction as a simplified system, we show that the conductance
enhancement can be explained in terms of the junctions energy spectrum. These
results are relevant for spintronics because they demonstrate that the TMR in
double junctions can be tuned and enhanced by varying the in-between metallic
layer's thickness.

###Enhanced tunneling magnetoresistance in Fe$\mid$ZnSe double junctions|J. Peralta-Ramos,A. M. Llois###

Enhanced tunneling magnetoresistance in Fe$\mid$ZnSe double junctions. We calculate the tunneling magnetoresistance (TMR) of
Fe$\mid$ZnSe$\mid$Fe$\mid$ZnSe$\mid$Fe (001) double magnetic tunnel junctions
as a function of the in-between Fe layer's thickness, and compare these results
with those of Fe$\mid$ZnSe$\mid$Fe simple junctions. The electronic band
structures are modeled by a parametrized tight-binding Hamiltonian fitted to
{\it ab initio} calculations, and the conductance is calculated within the
Landauer formalism expressed in terms of Green's functions. We find that the
conductances for each spin channel and the TMR strongly depend on the
in-between Fe layer's thickness, and that in some cases they are enhanced with
respect to simple junctions, in qualitative agreement with recent experimental
studies performed on similar systems. By using a 2D double junction as a
simplified system, we show that the conductance enhancement can be explained in
terms of the junctions energy spectrum. These results are relevant for
spintronics because they demonstrate that the TMR in double junctions can be
tuned and enhanced by varying the in-between metallic layer's thickness.

###Theory of Zero-Bias Anomaly in Magnetic Tunnel Junctions: Inelastic Tunneling via Impurities|L. Sheng,D. Y. Xing,D. N. Sheng###

Theory of Zero-Bias Anomaly in Magnetic Tunnel Junctions: Inelastic Tunneling via Impurities. Using the closed-time path integral approach, we nonperturbatively study
inelastic tunneling of electrons via magnetic impurities in the barrier
accompanied by phonon emission in a magnetic tunnel junction. The spectrum
density of phonon emission is found to show a power-law infrared singularity
$\sim\omega^{-(1-g)}$ with $g$ the dimensionless electron-phonon coupling. As a
consequence, the tunneling conductance $G(V)$ increases with bias voltage $|
V|$ as $G(V)-G(0)\sim| V|^{2g}$, exhibiting a discontinuity in slope at V=0 for
$g\le 0.5$. This theory can reproduce both cusp-like and non-cusp-like feature
of the zero-bias anomaly of tunneling resistance and magnetoresistance widely
observed in experiments.

###Tunnel magnetoresistance in magnetic tunnel junctions with embedded nanoparticles|Arthur Useinov,Niazbeck Useinov,Lin-Xiu Ye,Te-Ho Wu,Chih-Huang Lai###

Tunnel magnetoresistance in magnetic tunnel junctions with embedded nanoparticles. In this paper, we attempt the theoretical modeling of the magnetic tunnel
junctions with embedded magnetic and nonmagnetic nanoparticles (NPs). A few
abnormal tunnel magnetoresistance (TMR) effects, observed in related
experiments, can be easily simulated within our model: we found, that the
suppressed TMR magnitudes and the TMR sign-reversing effect at small voltages
are related to the electron momentum states of the NP located inside the
insulating layer. All these TMR behaviors can be explained within the tunneling
model, where NP is simulated as a quantum well (QW). The coherent (direct)
double barrier tunneling is dominating over the single barrier one. The origin
of the TMR suppression is the quantized angle transparency for spin polarized
electrons being in one of the lowest QW states. The phenomenon was classified
as the quantized conductance regime due to restricted geometry.

###Local density of states as a probe for tunneling magnetoresistance effect: application to ferrimagnetic tunnel junctions|Katsuhiro Tanaka,Takuya Nomoto,Ryotaro Arita###

Local density of states as a probe for tunneling magnetoresistance effect: application to ferrimagnetic tunnel junctions. We investigate the tunneling magnetoresistance (TMR) effect using the lattice
models which describe the magnetic tunnel junctions (MTJ). First, taking a
conventional ferromagnetic MTJ as an example, we show that the product of the
local density of states (LDOS) at the center of the barrier traces the TMR
effect qualitatively. The LDOS inside the barrier has the information on the
electrodes and the electron tunneling through the barrier, which enables us to
easily evaluate the tunneling conductance more precisely than the conventional
Julliere's picture. We then apply this method to the MTJs with collinear
ferrimagnets and antiferromagnets. We find that the TMR effect in the
ferrimagnetic and antiferromagnetic MTJs changes depending on the interfacial
magnetic structures originating from the sublattice structure, which can also
be captured by the LDOS. Our findings will reduce the computational cost for
the qualitative evaluation of the TMR effect, and be useful for a broader
search for the materials which work as the TMR devices showing high
performance.

###The Origin of Tunneling Anisotropic Magnetoresistance in Break Junctions|J. D. Burton,R. F. Sabirianov,J. P. Velev,O. N. Mryasov,E. Y. Tsymbal###

The Origin of Tunneling Anisotropic Magnetoresistance in Break Junctions. First-principles calculations of electron tunneling transport in Ni and Co
break junctions reveal strong dependence of the conductance on the
magnetization direction, an effect known as tunneling anisotropic
magnetoresistance (TAMR). The origin of this phenomenon stems from resonant
states localized in the electrodes near the junction break. The energy and
broadening of these states is strongly affected by the magnetization
orientation due to spin-orbit coupling, causing TAMR to be sensitive to bias
voltage on a scale of a few mV. Our results bear a resemblance to recent
experimental data and suggest that TAMR driven by resonant states is a general
phenomenon typical for magnetic broken contacts and other experimental
geometries where a magnetic tip is used to probe electron transport.

###Oscillatory tunneling magnetoresistance in magnetic tunnel junctions with inserted nonmagnetic layer|Changsik Choi,Byung Chan Lee###

Oscillatory tunneling magnetoresistance in magnetic tunnel junctions with inserted nonmagnetic layer. Oscillatory tunneling magnetoresistance (TMR) as a function of spacer
thickness is investigated theoretically for a magnetic tunnel junction with a
nonmagnetic layer inserted between the tunnel barrier and the ferromagnetic
layer. TMR is characterized in an analytical form, that is expressed with the
transmission and reflection amplitudes of single interfaces at the Fermi level,
and by the extremal wavevectors. Electronic structures with multiple bands are
taken into account in the derivation characterizing the TMR, and the proposed
analytical expression can be directly applied to real junctions. Based on our
model, the features of TMR dependence on spacer thickness are discussed,
including selection rules for the oscillation period. Numerical calculations
are performed using an envelope-function theory for several cases, and we show
that our model is in good agreement with the exact result.

###Magnetic tunnel junctions based on ferroelectric Hf0.5Zr0.5O2 tunnel barriers|Yingfen Wei,Sylvia Matzen,Guillaume Agnus,Mart Salverda,Pavan Nukala,Thomas Maroutian,Qihong Chen,Jianting Ye,Philippe Lecoeur,Beatriz Noheda###

Magnetic tunnel junctions based on ferroelectric Hf0.5Zr0.5O2 tunnel barriers. A ferroelectric tunnel barrier in between two ferromagnetic electrodes
(multiferroic tunnel junction, MFTJ), is one of the most promising concepts for
future microelectronic devices. In parallel, Hafnia based ferroelectrics are
showing great potential for device miniaturization down to the nanoscale. Here
we utilize ferroelectric Hf0.5Zr0.5O2 (HZO) with thickness of only 2 nm,
epitaxially grown on La0.7Sr0.3MnO3 (LSMO) ferromagnetic electrodes, as a large
band-gap insulating barrier integrated in MFTJs with cobalt top electrodes. As
previously reported for other MFTJs with similar electrodes, the tunneling
magnetoresistance (TMR) can be tuned and its sign can even be reversed by the
bias voltage across the junction. We demonstrate four non-volatile resistance
states generated by magnetic and electric field switching with high
reproducibility in this system.

###Shadow Bands and Tunneling Magnetoresistance in Itinerant Electron Ferromagnets|A. H. MacDonald,T. Jungwirth,M. Kasner###

Shadow Bands and Tunneling Magnetoresistance in Itinerant Electron Ferromagnets. In itinerant electron ferromagnets spectral weight is transferred at finite
temperatures from quasiparticle peaks located at majority and minority-spin
band energies to shadow-band peaks. For a given Bloch wavevector and band
index, the majority-spin shadow-band peak is located near the minority-spin
quasiparticle energy and the minority-spin shadow-band peak is located near the
majority-spin quasiparticle energy. This property can explain much of the
temperature dependence seen in the magnetoresistance of magnetic tunnel
junctions.

###Boosting room temperature tunnel magnetoresistance in hybrid magnetic tunnel junctions under electric bias|César González-Ruano,Coriolan Tiusan,Michel Hehn,Farkhad G. Aliev###

Boosting room temperature tunnel magnetoresistance in hybrid magnetic tunnel junctions under electric bias. Spin-resolved electron symmetry filtering is a key mechanism behind giant
tunneling magnetoresistance (TMR) in Fe/MgO/Fe and similar magnetic tunnel
junctions (MTJs), providing room temperature functionality in modern spin
electronics. However, the core process of the electron symmetry filtering
breaks down under applied bias, dramatically reducing the TMR above 0.5 V. This
strongly hampers the application range of MTJs. To circumvent the problem,
resonant tunneling between ferromagnetic electrodes through quantum well states
in thin layers has been used so far. This mechanism, however, is mainly
effective at low temperatures. Here, a fundamentally different approach is
demonstrated, providing a strong TMR boost under applied bias in
V/MgO/Fe/MgO/Fe/Co hybrids. This pathway uses spin orbit coupling (SOC)
controlled interfacial states in vanadium, which contrary to the V(001) bulk
states are allowed to tunnel to Fe(001) at low biases. The experimentally
observed strong increase of TMR with bias is modelled using two nonlinear
resistances in series, with the low bias conductance of the first (V/MgO/Fe)
element being boosted by the SOC-controlled interfacial states, while the
conductance of the second (Fe/MgO/Fe) junctions controlled by the relative
alignment of the two ferromagnetic layers. These results pave a way to
unexplored and fundamentally different spintronic device schemes, with
tunneling magnetoresistance uplifted under applied electric bias.

###Ferromagnetic tunneling junctions at low voltages: elastic versus inelastic scattering at $T=0 K$|C. A. Dartora,G. G. Cabrera###

Ferromagnetic tunneling junctions at low voltages: elastic versus inelastic scattering at $T=0 K$. In this paper we analyze different contributions to the magnetoresistance of
magnetic tunneling junctions at low voltages. A substantial fraction of the
resistance drop with voltage can be ascribed to variations of the density of
states and the barrier transmission with the bias. However, we found that the
anomaly observed at zero bias and the magnetoresistance behavior at very small
voltages, point to the contribution of inelastic magnon-assisted tunneling. The
latter is described by a transfer parameter $T^{J}$, which is one or two orders
of magnitude smaller than $T^{d}$, the direct transmission for elastic
currents. Our theory is in excellent agreement with experimental data, yielding
estimated values of $T^{J}$ which are of the order of $T^{d}$ / $T^{J}$ ~ 40.

###Spin-torque memristors based on perpendicular magnetic tunnel junctions with a hybrid chiral texture|Xueying Zhang,Wenlong Cai,Mengxing Wang,Kaihua Cao,Tianrui Zhang,Houyi Cheng,Shaoxin Li,Daoqian Zhu,Weisheng Zhao###

Spin-torque memristors based on perpendicular magnetic tunnel junctions with a hybrid chiral texture. Spin-torque memristors were proposed in 2009, which could provide fast,
low-power and infinite memristive behavior for large-density non-volatile
memory and neuromorphic computing. However, the strict requirements of
combining high magnetoresistance, stable intermediate states and spin-polarized
current switching in a single device pose difficulties in physical
implementation. Here, we experimentally demonstrate a nanoscale spin-torque
memristor based on a perpendicular-anisotropy magnetic tunnel junction with a
CoFeB/W/CoFeB composite free layer structure. Its tunneling magnetoresistance
is higher than 200%, and memristive behavior can be realized by spin-transfer
torque switching. Memristive states are maintained by robust domain wall
pinning around clusters of W atoms, where nanoscale vertical chiral spin
textures could be formed through the competition between opposing
Dzyaloshinskii-Moriya interactions and the fluctuating interlayer coupling
caused by the Ruderman-Kittel-Kasuya-Yosida interaction between the two CoFeB
free layers. Spike-timing-dependent plasticity is also demonstrated in this
device.

###Spin filtering effect in intrinsic 2D magnetic semiconductor Cr2Ge2Te6|Honglei Feng,Gang Shi,Dayu Yan,Yong Li,Youguo Shi,Yang Xu,Peng Xiong,Yongqing Li###

Spin filtering effect in intrinsic 2D magnetic semiconductor Cr2Ge2Te6. All van der Waals (vdW) Fe3GeTe2/Cr2Ge2Te6/graphite magnetic heterojunctions
have been fabricated via mechanical exfoliation and stacking, and their
magnetotransport properties are studied in detail. At low bias voltages large
negative junction magnetoresistances have been observed and are attributed to
spin-conserving tunneling transport across the insulating Cr2Ge2Te6 layer. With
increasing bias, a crossover to Fowler-Nordheim tunneling takes place. The
negative sign of the tunneling magnetoresistance (TMR) suggests that the bottom
of conduction band in Cr2Ge2Te6 belongs to minority spins, opposite to the
findings of some first-principles calculations. This work shows that the vdW
heterostructures based on 2D magnetic insulators are a valuable platform to
gain further insight into spin polarized tunneling transport, which is the
basis for pursuing high performance spintronic devices and a large variety of
quantum phenomena.

###Influence of chemical and magnetic interface properties of Co-Fe-B / MgO / Co-Fe-B tunnel junctions on the annealing temperature dependence of the magnetoresistance|J. Schmalhorst,A. Thomas,G. Reiss,X. Kou,E. Arenholz###

Influence of chemical and magnetic interface properties of Co-Fe-B / MgO / Co-Fe-B tunnel junctions on the annealing temperature dependence of the magnetoresistance. The knowledge of chemical and magnetic conditions at the Co40Fe40B20 / MgO
interface is important to interpret the strong annealing temperature dependence
of tunnel magnetoresistance of Co-Fe-B / MgO / Co-Fe-B magnetic tunnel
junctions, which increases with annealing temperature from 20% after annealing
at 200C up to a maximum value of 112% after annealing at 350C. While the well
defined nearest neighbor ordering indicating crystallinity of the MgO barrier
does not change by the annealing, a small amount of interfacial Fe-O at the
lower Co-Fe-B / MgO interface is found in the as grown samples, which is
completely reduced after annealing at 275C. This is accompanied by a
simultaneous increase of the Fe magnetic moment and the tunnel
magnetoresistance. However, the TMR of the MgO based junctions increases
further for higher annealing temperature which can not be caused by Fe-O
reduction. The occurrence of an x-ray absorption near-edge structure above the
Fe and Co L-edges after annealing at 350C indicates the recrystallization of
the Co-Fe-B electrode. This is prerequisite for coherent tunneling and has been
suggested to be responsible for the further increase of the TMR above 275C.
Simultaneously, the B concentration in the Co-Fe-B decreases with increasing
annealing temperature, at least some of the B diffuses towards or into the MgO
barrier and forms a B2O3 oxide.

###Spin effects in single electron tunneling|J. Barnas,I. Weymann###

Spin effects in single electron tunneling. An important consequence of the discovery of giant magnetoresistance in
metallic magnetic multilayers is a broad interest in spin dependent effects in
electronic transport through magnetic nanostructures. An example of such
systems are tunnel junctions -- single-barrier planar junctions or more complex
ones. In this review we present and discuss recent theoretical results on
electron and spin transport through ferromagnetic mesoscopic junctions
including two or more barriers. Such systems are also called ferromagnetic
single-electron transistors. We start from the situation when the central part
of a device has the form of a magnetic (or nonmagnetic) metallic nanoparticle.
Transport characteristics reveal then single-electron charging effects,
including the Coulomb staircase, Coulomb blockade, and Coulomb oscillations.
Single-electron ferromagnetic transistors based on semiconductor quantum dots
and large molecules (especially carbon nanotubes) are also considered. The main
emphasis is placed on the spin effects due to spin-dependent tunnelling through
the barriers, which gives rise to spin accumulation and tunnel
magnetoresistance. Spin effects also occur in the current-voltage
characteristics, (differential) conductance, shot noise, and others. Transport
characteristics in the two limiting situations of weak and strong coupling are
of particular interest. In the former case we distinguish between the
sequential tunnelling and cotunneling regimes. In the strong coupling regime we
concentrate on the Kondo phenomenon, which in the case of transport through
quantum dots or molecules leads to an enhanced conductance and to a pronounced
zero-bias Kondo peak in the differential conductance.

###State of Co and Mn in half-metallic ferromagnet Co$_2$MnSi explored by magnetic circular dichroism in hard X-ray photoelectron emission and soft X-ray absorption spectroscopies|Gerhard H. Fecher,Daniel Ebke,Siham Ouardi,Stefano Agrestini,Chang-Yang Kuo,Nils Hollmann,Zhiwei Hu,Andrei Gloskovskii,Flora Yakhou,Nicholas B. Brookes,Claudia Felser###

State of Co and Mn in half-metallic ferromagnet Co$_2$MnSi explored by magnetic circular dichroism in hard X-ray photoelectron emission and soft X-ray absorption spectroscopies. The half-metallic Heusler compound Co$_2$MnSi is a very attractive material
for spintronic devices because it exhibits very high tunnelling
magnetoresistance ratios. This work reports on a spectroscopic investigation of
thin Co$_2$MnSi films as they are used as electrodes in magnetic tunnel
junctions. The investigated films exhibit a remanent in-plane magnetisation
with a magnetic moment of about 5~$\mu_B$ when saturated, as expected. The low
coercive field of only 4~mT indicates soft magnetic behaviour. Magnetic
dichroism in emission and absorption was measured at the Co and Mn $2p$ core
levels. The photoelectron spectra were excited by circularly polarised hard
X-rays with an energy of of 6~keV and taken from the remanently magnetised
film. The soft X-ray absorption spectra were taken in an induction field of
4~T. Both methods yielded large dichroism effects. An analysis reveals the
localised character of the electrons and magnetic moments attributed to the Mn
atoms, whereas the electrons related to the Co atoms contribute an itinerant
part to the total magnetic moment.

###Anisotropic magnetoresistance and anisotropic tunneling magnetoresistance due to quantum interference in ferromagnetic metal break junctions|Kirill I. Bolotin,Ferdinand Kuemmeth,D. C. Ralph###

Anisotropic magnetoresistance and anisotropic tunneling magnetoresistance due to quantum interference in ferromagnetic metal break junctions. We measure the low-temperature resistance of permalloy break junctions as a
function of contact size and the magnetic field angle, in applied fields large
enough to saturate the magnetization. For both nanometer-scale metallic
contacts and tunneling devices we observe large changes in resistance with
angle, as large as 25% in the tunneling regime. The pattern of
magnetoresistance is sensitive to changes in bias on a scale of a few mV. We
interpret the effect as a consequence of conductance fluctuations due to
quantum interference.

###Large bias-dependent magnetoresistance in all-oxide magnetic tunnel junctions with a ferroelectric barrier|Nuala M. Caffrey,Thomas Archer,Ivan Rungger,Stefano Sanvito###

Large bias-dependent magnetoresistance in all-oxide magnetic tunnel junctions with a ferroelectric barrier. All-oxide magnetic tunnel junctions (MTJs) incorporating functional materials
as insulating barriers have the potential of becoming the founding technology
for novel multi-functional devices. We investigate, by first-principles density
functional theory, the bias-dependent transport properties of an all-oxide
SrRuO3/BaTiO3/SrRuO3 MTJ. This incorporates a BaTiO3 barrier which can be found
either in a non-ferroic or in a ferroelectric state. In such an MTJ not only
can the tunneling magnetoresistance reach enormous values, but also, for
certain voltages, its sign can be changed by altering the barrier electric
state. These findings pave the way for a new generation of
electrically-controlled magnetic sensors.

###Reversal of spin polarization in Fe/GaAs (001) driven by resonant surface states: First-principles calculations|Athanasios N. Chantis,Kirill D. Belashchenko,Darryl L. Smith,Evgeny Y. Tsymbal,Mark van Schilfgaarde,Robert C. Albers###

Reversal of spin polarization in Fe/GaAs (001) driven by resonant surface states: First-principles calculations. A minority-spin resonant state at the Fe/GaAs(001) interface is predicted to
reverse the spin polarization with voltage bias of electrons transmitted across
this interface. Using a Green's function approach within the local spin density
approximation we calculate spin-dependent current in a Fe/GaAs/Cu tunnel
junction as a function of applied bias voltage. We find a change in sign of the
spin polarization of tunneling electrons with bias voltage due to the interface
minority-spin resonance. This result explains recent experimental data on spin
injection in Fe/GaAs contacts and on tunneling magnetoresistance in Fe/GaAs/Fe
magnetic tunnel junctions.

###Effect of interfacial strain on spin injection and spin polarization of Co2CrAl/NaNbO3/Co2CrAl magnetic tunneling junction|Yongqing Cai,Zhaoqiang Bai,Ming Yang,Yuan Ping Feng###

Effect of interfacial strain on spin injection and spin polarization of Co2CrAl/NaNbO3/Co2CrAl magnetic tunneling junction. First-principles calculations were carried out to investigate interfacial
strain effects on spin injection and spin polarization of a magnetic tunnel
junction consisting of half-metallic full-Heusler alloy Co2CrAl and
ferroelectric perovskite NaNbO3. Spin-dependent coherent tunneling was
calculated within the framework of non-equilibrium Green's function technique.
Both spin polarization and tunnel magnetoresistance (TMR) are affected by the
interfacial strain but their responses to compressive and tensile strains are
different. Spin polarization across the interface is fully preserved under a
compressive strain due to stronger coupling between interfacial atoms, whereas
a tensile strain significantly enhances interface states and lead to
substantial drops in spin polarization and TMR.

###Giant anisotropic magnetoresistance in Ising superconductor-magnetic insulator tunnel junctions|Kaifei Kang,Shengwei Jiang,Helmuth Berger,Kenji Watanabe,Takashi Taniguchi,László Forró,Jie Shan,Kin Fai Mak###

Giant anisotropic magnetoresistance in Ising superconductor-magnetic insulator tunnel junctions. Superconductivity and magnetism are generally incompatible because of the
opposing requirement on electron spin alignment. When combined, they produce a
multitude of fascinating phenomena, including unconventional superconductivity
and topological superconductivity. The emergence of two-dimensional (2D)layered
superconducting and magnetic materials that can form nanoscale junctions with
atomically sharp interfaces presents an ideal laboratory to explore new
phenomena from coexisting superconductivity and magnetic ordering. Here we
report tunneling spectroscopy under an in-plane magnetic field of
superconductor-ferromagnet-superconductor (S/F/S) tunnel junctions that are
made of 2D Ising superconductor NbSe2 and ferromagnetic insulator CrBr3. We
observe nearly 100% tunneling anisotropic magnetoresistance (AMR), that is,
difference in tunnel resistance upon changing magnetization direction from
out-of-plane to inplane. The giant tunneling AMR is induced by
superconductivity, particularly, a result of interfacial magnetic exchange
coupling and spin-dependent quasiparticle scattering. We also observe an
intriguing magnetic hysteresis effect in superconducting gap energy and
quasiparticle scattering rate with a critical temperature that is 2 K below the
superconducting transition temperature. Our study paves the path for exploring
superconducting spintronic and unconventional superconductivity in van der
Waals heterostructures.

###Magneto-ionic control of spin polarization in magnetic tunnel junctions|Yingfen Wei,Sylvia Matzen,Cynthia P. Quinteros,Thomas Maroutian,Guillaume Agnus,Philippe Lecoeur,Beatriz Noheda###

Magneto-ionic control of spin polarization in magnetic tunnel junctions. Magnetic tunnel junctions (MTJs) with Hf0.5Zr0.5O2 barriers are reported to
show both tunneling magnetoresistance effect (TMR) and tunneling
electroresistance effect (TER), displaying four resistance states by magnetic
and electric field switching. Here we show that, under electric field cycling
of large enough magnitude, the TER can reach values as large as 10^6%.
Moreover, concomitant with this TER enhancement, the devices develop electrical
control of spin polarization, with sign reversal of the TMR effect. Currently,
this intermediate state exists for a limited number of cycles and understanding
the origin of these phenomena is key to improve its stability. The experiments
presented here point to the magneto-ionic effect as the origin of the large TER
and strong magneto-electric coupling, showing that ferroelectric polarization
switching of the tunnel barrier is not the main contribution.

###Theory of the ac spin-valve effect|Denis Kochan,Martin Gmitra,Jaroslav Fabian###

Theory of the ac spin-valve effect. The spin-valve complex magnetoimpedance of symmetric ferromagnet/normal
metal/ferromagnet junctions is investigated within the drift-diffusion
(standard) model of spin injection. The ac magnetoresistance---the real part
difference of the impedances of the parallel and antiparallel magnetization
configurations---exhibits an overall damped oscillatory behavior, as an
interplay of the diffusion and spin relaxation times. In wide junctions the ac
magnetoresistance oscillates between positive and negative values, reflecting
resonant amplification and depletion of the spin accumulation, while the line
shape for thin tunnel junctions is predicted to be purely Lorentzian. The ac
spin-valve effect could be a technique to extract spin transport and spin
relaxation parameters in the absence of a magnetic field and for a fixed sample
size.

###Gate control of the tunneling magnetoresistance in double-barrier junctions|J. Peralta-Ramos,A. M. Llois###

Gate control of the tunneling magnetoresistance in double-barrier junctions. We calculate the conductances and the tunneling magnetoresistance (TMR) of
double magnetic tunnel junctions, taking as a model example junctions composed
of Fe/ZnSe/Fe/ZnSe/Fe (001). The calculations are done as a function of the
gate voltage applied to the in-between Fe layer slab. We find that the
application of a gate voltage to the in-between Fe slab strongly affects the
junctions' TMR due to the tuning or untuning of conductance resonances mediated
by quantum well states. The gate voltage allows a significant enhancement of
the TMR, in a more controllable way than by changing the thickness of the
in-between Fe slab. This effect may be useful in the design of future
spintronic devices based on the TMR effect, requiring large and controllable
TMR values.

###Evidence of Klein tunneling in graphene p-n junctions|N. Stander,B. Huard,D. Goldhaber-Gordon###

Evidence of Klein tunneling in graphene p-n junctions. Transport through potential barriers in graphene is investigated using a set
of metallic gates capacitively coupled to graphene to modulate the potential
landscape. When a gate-induced potential step is steep enough, disorder becomes
less important and the resistance across the step is in quantitative agreement
with predictions of Klein tunneling of Dirac fermions up to a small correction.
We also perform magnetoresistance measurements at low magnetic fields and
compare them to recent predictions.

###Magnetization reversal in sub-100nm magnetic tunnel junctions with ultrathin MgO barrier biased along hard axis|J. P. Cascales,D. Herranz,J. L. Sambricio,U. Ebels,J. A. Katine,F. G. Aliev###

Magnetization reversal in sub-100nm magnetic tunnel junctions with ultrathin MgO barrier biased along hard axis. We report on room temperature magnetoresistance and low frequency noise in
sub-100nm elliptic CoFeB/MgO/CoFeB magnetic tunnel junctions with ultrathin
(0.9nm) barriers. For magnetic fields applied along the hard axis, we observe
current induced magnetization switching between the antiparallel and parallel
alignments at DC current densities as low as 4*106A/cm2. We attribute the low
value of the critical current to the influence of localized reductions in the
tunnel barrier, which affects the current distribution. The analysis of random
telegraph noise, which appears in the field interval near a magnetization
switch, provides an estimate to the dimension of the pseudo pinholes that
trigger the magnetization switching via local spin torque. Micromagnetic
simulations qualitatively and quantitatively reproduce the main experimental
observations.

###Impurity induced enhancement of perpendicular magnetic anisotropy in Fe/MgO tunnel junctions|A. Hallal,B. Dieny,M. Chshiev###

Impurity induced enhancement of perpendicular magnetic anisotropy in Fe/MgO tunnel junctions. Using first-principles calculations, we investigated the impact of chromium
(Cr) and vanadium (V) impurities on the magnetic anisotropy and spin
polarization in Fe/MgO magnetic tunnel junctions. It is demonstrated using
layer resolved anisotropy calculation technique, that while the impurity near
the interface has a drastic effect in decreasing the perpendicular magnetic
anisotropy (PMA), its position within the bulk allows maintaining high surface
PMA. Moreover, the effective magnetic anisotropy has a strong tendency to go
from in-plane to out-of-plane character as a function of Cr and V concentration
favoring out-of-plane magnetization direction for ~1.5 nm thick Fe layers at
impurity concentrations above 20 %. At the same time, spin polarization is not
affected and even enhanced in most situations favoring an increase of tunnel
magnetoresistance (TMR) values.

###Domain Wall-Magnetic Tunnel Junction Analog Content Addressable Memory Using Current and Projected Data|Harrison Jin,Hanqing Zhu,Keren Zhu,Thomas Leonard,Jaesuk Kwon,Mahshid Alamdar,Kwangseok Kim,Jungsik Park,Naoki Hase,David Z. Pan,Jean Anne C. Incorvia###

Domain Wall-Magnetic Tunnel Junction Analog Content Addressable Memory Using Current and Projected Data. With the rise in in-memory computing architectures to reduce the
compute-memory bottleneck, a new bottleneck is present between analog and
digital conversion. Analog content-addressable memories (ACAM) are being
recently studied for in-memory computing to efficiently convert between analog
and digital signals. Magnetic memory elements such as magnetic tunnel junctions
(MTJs) could be useful for ACAM due to their low read/write energy and high
endurance, but MTJs are usually restricted to digital values. The spin orbit
torque-driven domain wall-magnetic tunnel junction (DW-MTJ) has been recently
shown to have multi-bit function. Here, an ACAM circuit is studied that uses
two domain wall-magnetic tunnel junctions (DW-MTJs) as the analog storage
elements. Prototype DW-MTJ data is input into the magnetic ACAM (MACAM) circuit
simulation, showing ternary CAM function. Device-circuit co-design is carried
out, showing that 8-10 weight bits are achievable, and that designing
asymmetrical spacing of the available DW positions in the device leads to
evenly spaced ACAM search bounds. Analyzing available spin orbit torque
materials shows platinum provides the largest MACAM search bound while still
allowing spin orbit torque domain wall motion, and that the circuit is
optimized with minimized MTJ resistance, minimized spin orbit torque material
resistance, and maximized tunnel magnetoresistance. These results show the
feasibility of using DW-MTJs for MACAM and provide design parameters.

###Controlled Electrode Magnetization Alignment in Planar Elliptical Ferromagnetic Break Junction Devices|Gavin D. Scott,Ting-Chen Hu###

Controlled Electrode Magnetization Alignment in Planar Elliptical Ferromagnetic Break Junction Devices. Controlling the magnetization reversal process of magnetic elements is
important for a wide range of applications that make use of magnetoresistive
effects, but is difficult to achieve for devices that require adjacent thin
film structures capable of contacting an individual molecule or quantum dot. We
report on the fabrication and measurement of ferromagnetic break junction
devices with planar, elliptical leads to address the particular challenge of
controlling the relative magnetization alignment between neighboring
electrodes. Low temperature transport measurements, supported by finite-element
micromagnetic simulations, are used to characterize the magnetoresistance
response across a range of conductance levels. We demonstrate that an in-plane
external field applied parallel to the hard axis of the ellipses may be used to
controllably switch the magnetization of the source and drain electrodes
between monodomain-like parallel and antiparallel configurations for devices in
the tunneling regime.

###Scaling Projections on Spin Transfer Torque Magnetic Tunnel Junctions|Debasis Das,Ashwin Tulapurkar,Bhaskaran Muralidharan###

Scaling Projections on Spin Transfer Torque Magnetic Tunnel Junctions. We investigate scaling of technologically relevant magnetic tunnel junction
devices in the trilayer and pentalayer configurations by varying the
cross-sectional area along the transverse direction using the non-equilibrium
Green's function spin transport formalism. We study the geometry dependence by
considering square and circular cross-sections. As the transverse dimension in
each case reduces, we demonstrate that the transverse mode energy profile plays
a major role in the resistance-area product. Both types of devices show
constant tunnel magnetoresistance at larger cross-sectional areas but achieve
ultra-high magnetoresistance at small cross-sectional areas, while maintaining
low resistance-area products. We notice that although the critical switching
voltage for switching the magnetization of the free layer nanomagnet in the
trilayer case remains constant at larger areas, it needs more energy to switch
at smaller areas. In the pentalayer case, we observe an oscillatory behavior at
smaller areas as a result of double barrier tunneling. We also describe how
switching characteristics of both kinds of devices are affected by the scaling.

###Voltage and temperature dependence of the grain boundary tunneling magnetoresistance in manganites|C. Hoefener,J. B. Philipp,J. Klein,L. Alff,A. Marx,B. Buechner,R. Gross###

Voltage and temperature dependence of the grain boundary tunneling magnetoresistance in manganites. We have performed a systematic analysis of the voltage and temperature
dependence of the tunneling magnetoresistance (TMR) of grain boundaries (GB) in
the manganites. We find a strong decrease of the TMR with increasing voltage
and temperature. The decrease of the TMR with increasing voltage scales with an
increase of the inelastic tunneling current due to multi-step inelastic
tunneling via localized defect states in the tunneling barrier. This behavior
can be described within a three-current model for magnetic tunnel junctions
that extends the two-current Julliere model by adding an inelastic,
spin-independent tunneling contribution. Our analysis gives strong evidence
that the observed drastic decrease of the GB-TMR in manganites is caused by an
imperfect tunneling barrier.

###Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures|Shouzhong Peng,Mengxing Wang,Hongxin Yang,Lang Zeng,Jiang Nan,Jiaqi Zhou,Youguang Zhang,Ali Hallal,Mairbek Chshiev,Kang L. Wang,Qianfan Zhang,Weisheng Zhao###

Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures. Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts
extensive attentions due to its non-volatility, high density and low power
consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel
junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well
as a large value of perpendicular magnetic anisotropy (PMA). It has been
experimentally proven that a capping layer coating on CoFeB layer is essential
to obtain a strong PMA. However, the physical mechanism of such effect remains
unclear. In this paper, we investigate the origin of the PMA in
MgO/CoFe/metallic capping layer structures by using a first-principles
computation scheme. The trend of PMA variation with different capping materials
agrees well with experimental results. We find that interfacial PMA in the
three-layer structures comes from both the MgO/CoFe and CoFe/capping layer
interfaces, which can be analyzed separately. Furthermore, the PMAs in the
CoFe/capping layer interfaces are analyzed through resolving the magnetic
anisotropy energy by layer and orbital. The variation of PMA with different
capping materials is attributed to the different hybridizations of both d and p
orbitals via spin-orbital coupling. This work can significantly benefit the
research and development of nanoscale STT-MRAM.

###Probing magnetism in 2D van der Waals crystalline insulators via electron tunneling|Dahlia R. Klein,David MacNeill,Jose L. Lado,David Soriano,Efrén Navarro-Moratalla,Kenji Watanabe,Takashi Taniguchi,Soham Manni,Paul Canfield,Joaquín Fernández-Rossier,Pablo Jarillo-Herrero###

Probing magnetism in 2D van der Waals crystalline insulators via electron tunneling. Magnetic insulators are a key resource for next-generation spintronic and
topological devices. The family of layered metal halides promises ultrathin
insulating multiferroics, spin liquids, and ferromagnets, but new
characterization methods are required to unlock their potential. Here, we
report tunneling through the layered magnetic insulator CrI3 as a function of
temperature and applied magnetic field. We electrically detect the magnetic
ground state and inter-layer coupling and observe a field-induced metamagnetic
transition. The metamagnetic transition results in magnetoresistances of 95%,
300%, and 550% for bilayer, trilayer, and tetralayer CrI3 barriers,
respectively. We further measure inelastic tunneling spectra for our junctions,
unveiling a rich spectrum of collective magnetic excitations (magnons) in CrI3.
Our results establish vertical tunneling as a versatile probe of magnetism in
atomically thin insulators.

###Assisted Tunneling in Ferromagnetic Junctions and Half-Metallic Oxides|A. M. Bratkovsky###

Assisted Tunneling in Ferromagnetic Junctions and Half-Metallic Oxides. Different mechanisms of spin-dependent tunneling are analyzed with respect to
their role in tunnel magnetoresistance (TMR). Microscopic calculation within a
realistic model shows that direct tunneling in iron group systems leads to
about a 30% change in resistance, which is close but lower than experimentally
observed values. The larger observed values of the tunnel magnetoresistance
(TMR) might be a result of tunneling involving surface polarized states. It is
found that tunneling via resonant defect states in the barrier radically
decreases the TMR by order of magnitude. One-magnon emission is shown to reduce
the TMR, whereas phonons increase the effect. The inclusion of both magnons and
phonons reasonably explains an unusual bias dependence of the TMR. The model
presented here is applied qualitatively to half-metallics with 100% spin
polarization, where one-magnon processes are suppressed and the change in
resistance in the absence of spin-mixing on impurities may be arbitrarily
large. Even in the case of imperfect magnetic configurations, the resistance
change can be a few 1000 percent. Examples of half-metallic systems are
CrO2/TiO2 and CrO2/RuO2.

###Tunnel magnetoresistance and robust room temperature exchange bias with multiferroic BiFeO3 epitaxial thin films|H. Bea,M. Bibes,S. Cherifi,F. Nolting,B. Warot-Fonrose,S. Fusil,G. Herranz,C. Deranlot,E. Jacquet,K. Bouzehouane,A. Barthelemy###

Tunnel magnetoresistance and robust room temperature exchange bias with multiferroic BiFeO3 epitaxial thin films. We report on the functionalization of multiferroic BiFeO3 epitaxial films for
spintronics. A first example is provided by the use of ultrathin layers of
BiFeO3 as tunnel barriers in magnetic tunnel junctions with La2/3Sr1/3MnO3 and
Co electrodes. In such structures, a positive tunnel magnetoresistance up to
30% is obtained at low temperature. A second example is the exploitation of the
antiferromagnetic spin structure of a BiFeO3 film to induce a sizeable (~60 Oe)
exchange bias on a ferromagnetic film of CoFeB, at room temperature.
Remarkably, the exchange bias effect is robust upon magnetic field cycling,
with no indications of training.

###Skyrmions in magnetic tunnel junctions|Xueying Zhang,Wenlong Cai,Xichao Zhang,Zilu Wang,Zhi Li,Yu Zhang,Kaihua Cao,Na Lei,Wang Kang,Yue Zhang,Haiming Yu,Yan Zhou,Weisheng Zhao###

Skyrmions in magnetic tunnel junctions. In this work, we demonstrate that skyrmions can be nucleated in the free
layer of a magnetic tunnel junction (MTJ) with Dzyaloshinskii-Moriya
interactions (DMI) by a spin-polarized current with the assistance of stray
fields from the pinned layer. The size, stability and number of created
skyrmions can be tuned by either the DMI strength or the stray field
distribution. The interaction between the stray field and the DMI effective
field is discussed. A device with multi-level tunneling magnetoresistance is
proposed, which could pave the ways for skyrmion-MTJ-based multi-bit storage
and artificial neural network computation. Our results may facilitate the
efficient nucleation and electrical detection of skyrmions.

###Determination of spin-dependent Seebeck coefficients of CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars|N. Liebing,S. Serrano-Guisan,K. Rott,G. Reiss,J. Langer,B. Ocker,H. W. Schumacher###

Determination of spin-dependent Seebeck coefficients of CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars. We investigate the spin-dependent Seebeck coefficient and the tunneling
magneto thermopower of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) in the
presence of thermal gradients across the MTJ. Thermal gradients are generated
by an electric heater on top of the nanopillars. The thermo power voltage
across the MTJ is found to scale linearly with the heating power and reveals
similar field dependence as the tunnel magnetoresistance. The amplitude of the
thermal gradient is derived from calibration measurements in combination with
finite element simulations of the heat flux. Based on this, large
spin-dependent Seebeck coefficients of the order of (240 \pm 110) \muV/K are
derived. From additional measurements on MTJs after dielectric breakdown, a
tunneling magneto thermopower up to 90% can be derived for 1.5 nm MgO based MTJ
nanopillars.

###Nonvolatile Multilevel States in Multiferroic Tunnel Junctions|Mei Fang,Sangjian Zhang,Wenchao Zhang,Lu Jiang,Eric Vetter,Ho Nyung Lee,Xiaoshan Xu,Dali Sun,Jian Shen###

Nonvolatile Multilevel States in Multiferroic Tunnel Junctions. Manipulation of tunneling spin-polarized electrons via a ferroelectric
interlayer sandwiched between two ferromagnetic electrodes, dubbed Multiferroic
Tunnel Junctions (MFTJs), can be achieved not only by the magnetic alignments
of two ferromagnets but also by the electric polarization of the ferroelectric
interlayer, providing great opportunities for next-generation multi-state
memory devices. Here we show that a La0.67Sr0.33MnO3
(LSMO)/PbZr0.2Ti0.8O3(PZT)/Co structured MFTJ device can exhibit multilevel
resistance states in the presence of gradually reversed ferroelectric domains
via tunneling electro-resistance and tunneling magnetoresistance, respectively.
The nonvolatile ferroelectric control in the MFTJ can be attributed to separate
contributions arising from two independent ferroelectric channels in the PZT
interlayer with opposite polarization. Our study shows the dominant role of
"mixed" ferroelectric states on achieving accumulative electrical modulation of
multilevel resistance states in MFTJs, paving the way for multifunctional
device applications.

###Tunneling anisotropic magnetoresistance driven by resonant surface states: First-principles calculations of Fe(001) surface|Athanasios N. Chantis,Kirill D. Belashchenko,Evgeny Y. Tsymbal,Mark van Schilfgaarde###

Tunneling anisotropic magnetoresistance driven by resonant surface states: First-principles calculations of Fe(001) surface. Fully-relativistic first-principles calculations of the Fe(001) surface
demonstrate that resonant surface (interface) states may produce sizeable
tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a
single magnetic electrode. The effect is driven by the spin-orbit coupling. It
shifts the resonant surface band via the Rashba effect when the magnetization
direction changes. We find that spin-flip scattering at the interface is
controlled not only by the strength of the spin-orbit coupling, but depends
strongly on the intrinsic width of the resonant surface states.

###Large tunneling magnetoresistance in VSe2/MoS2 magnetic tunnel junction|Jiaqi Zhou,Junfeng Qiao,Chun-Gang Duan,Arnaud Bournel,Kang L. Wang,Weisheng Zhao###

Large tunneling magnetoresistance in VSe2/MoS2 magnetic tunnel junction. Two-dimensional (2D) van der Waals (vdW) materials provide the possibility of
realizing heterostructures with coveted properties. Here, we report a
theoretical investigation of the vdW magnetic tunnel junction (MTJ) based on
VSe2/MoS2 heterojunction, where the VSe2 monolayer acts as the ferromagnet with
the room-temperature ferromagnetism. We propose the concept of spin-orbit
torque (SOT) vdW MTJ with reliable reading and efficient writing operations.
The non-equilibrium study reveals a large tunneling magnetoresistance (TMR) of
846 % at 300 Kelvin, identifying significantly its parallel and anti-parallel
states. Thanks to the strong spin Hall conductivity of MoS2, SOT is promising
for the magnetization switching of VSe2 free layer. Quantum-well states come
into being and resonances appear in MTJ, suggesting that the voltage control
can adjust transport properties effectively. The SOT vdW MTJ based on VSe2/MoS2
provides desirable performance and experimental feasibility, offering new
opportunities for 2D spintronics.

###Extraordinary Tunneling Magnetoresistance in Antiferromagnetic Tunnel Junctions with Antiperovskite Electrodes|Gautam Gurung,Ding-Fu Shao,Evgeny Y. Tsymbal###

Extraordinary Tunneling Magnetoresistance in Antiferromagnetic Tunnel Junctions with Antiperovskite Electrodes. Recent theoretical predictions and experimental demonstrations of a large
tunneling magnetoresistance (TMR) effect in antiferromagnetic (AFM) tunnel
junctions (AFMTJs) offer a new paradigm for information technologies where the
AFM N\`eel vector serves as a state variable. A large TMR is beneficial for the
applications. Here, we predict the emergence of an extraordinary TMR (ETMR)
effect in AFMTJs utilizing noncollinear AFM antiperovskite XNMn$_{3}$ (X = Ga,
Sn,...) electrodes and a perovskite oxide ATiO$_{3}$ (A = Sr, Ba,...) barrier
layer. The ETMR effect stems from the perfectly spin-polarized electronic
states in the AFM antiperovskites that can efficiently tunnel through the
low-decay-rate evanescent states of the perovskite oxide while preserving their
spin state. Using an GaNMn$_{3}$/SrTiO$_{3}$/GaNMn$_{3}$ (001) AFMTJ as a
representative example, we demonstrate a giant TMR ratio exceeding $10^{4}$%
and originating from the ETMR effect. These results are promising for the
efficient detection and control of the N\`eel vector in AFM spintronics.

###Low frequency noise characteristics of sub-micron magnetic tunnel junctions|B. Zhong,Y. Chen,S. Garzon,T. M. Crawford,R. A. Webb###

Low frequency noise characteristics of sub-micron magnetic tunnel junctions. We report that low frequency (up to 200 kHz) noise spectra of magnetic tunnel
junctions with areas ~10^{-10}cm^2$ at 10 Kelvin deviate significantly from the
typical 1/f behavior found in large area junctions at room temperature. In most
cases, a Lorentzian-like shape with characteristic time between 0.1 and 10 ms
is observed, which indicates only a small number of fluctuators contribute to
the measured noise. By investigating the dependence of noise on both the
magnitude and orientation of an applied magnetic field, we find that
magnetization fluctuations in both free and reference layers are the main
sources of noise in these devices. At small fields, where the noise from the
free layer is dominant, a linear relation between the measured noise and
angular magnetoresistance susceptibility can be established.

###Tunable giant magnetoresistance in a single-molecule junction|Kai Yang,Hui Chen,Thomas Pope,Yibin Hu,Liwei Liu,Dongfei Wang,Lei Tao,Wende Xiao,Xiangmin Fei,Yu-Yang Zhang,Hong-Gang Luo,Shixuan Du,Tao Xiang,Werner A. Hofer,Hong-Jun Gao###

Tunable giant magnetoresistance in a single-molecule junction. Controlling electronic transport through a single-molecule junction is
crucial for molecular electronics or spintronics. In magnetic molecular
devices, the spin degree-of-freedom can be used to this end since the magnetic
properties of the magnetic ion centers fundamentally impact the transport
through the molecules. Here we demonstrate that the electron pathway in a
single-molecule device can be selected between two molecular orbitals by
varying a magnetic field, giving rise to a tunable anisotropic
magnetoresistance up to 93%. The unique tunability of the electron pathways is
due to the magnetic reorientation of the transition metal center, resulting in
a re-hybridization of molecular orbitals. We obtain the tunneling electron
pathways by Kondo effect, which manifests either as a peak or a dip line shape.
The energy changes of these spin-reorientations are remarkably low and less
than one millielectronvolt. The large tunable anisotropic magnetoresistance
could be used to control electronic transport in molecular spintronics.

###Nanoscopic processes of Current Induced Switching in thin tunnel junctions|J. Ventura,J. P. Araujo,J. B. Sousa,Y. Liu,Z. Zhang,P. P. Freitas###

Nanoscopic processes of Current Induced Switching in thin tunnel junctions. In magnetic nanostructures one usually uses a magnetic field to commute
between two resistance (R) states. A less common but technologically more
interesting alternative to achieve R-switching is to use an electrical current,
preferably of low intensity. Such Current Induced Switching (CIS) was recently
observed in thin magnetic tunnel junctions, and attributed to electromigration
of atoms into/out of the insulator. Here we study the Current Induced
Switching, electrical resistance, and magnetoresistance of thin
MnIr/CoFe/AlO$_x$/CoFe tunnel junctions. The CIS effect at room temperature
amounts to 6.9% R-change between the high and low states and is attributed to
nanostructural rearrangements of metallic ions in the electrode/barrier
interfaces. After switching to the low R-state some electro-migrated ions
return to their initial sites through two different energy channels. A low
(high) energy barrier of $\sim$0.13 eV ($\sim$0.85 eV) was estimated. Ionic
electromigration then occurs through two microscopic processes associated with
different types of ions sites/defects. Measurements under an external magnetic
field showed an additional intermediate R-state due to the simultaneous
conjugation of the MR (magnetic) and CIS (structural) effects.

###Giant Voltage Manipulation of MgO-based Magnetic Tunnel Junctions via Localized Anisotropic Strain: a Potential Pathway to Ultra-Energy-Efficient Memory Technology|Zhengyang Zhao,Mahdi Jamali,Noel D'Souza,Delin Zhang,Supriyo Bandyopadhyay,Jayasimha Atulasimha,Jian-Ping Wang###

Giant Voltage Manipulation of MgO-based Magnetic Tunnel Junctions via Localized Anisotropic Strain: a Potential Pathway to Ultra-Energy-Efficient Memory Technology. Strain-mediated voltage control of magnetization in
piezoelectric/ferromagnetic systems is a promising mechanism to implement
energy-efficient spintronic memory devices. Here, we demonstrate giant voltage
manipulation of MgO magnetic tunnel junctions (MTJ) on a
Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) piezoelectric substrate with (001)
orientation. It is found that the magnetic easy axis, switching field, and the
tunnel magnetoresistance (TMR) of the MTJ can be efficiently controlled by
strain from the underlying piezoelectric layer upon the application of a gate
voltage. Repeatable voltage controlled MTJ toggling between high/low-resistance
states is demonstrated. More importantly, instead of relying on the intrinsic
anisotropy of the piezoelectric substrate to generate the required strain, we
utilize anisotropic strain produced using local gating scheme, which is
scalable and amenable to practical memory applications. Additionally, the
adoption of crystalline MgO-based MTJ on piezoelectric layer lends itself to
high TMR in the strain-mediated MRAM devices.

###Domain Wall-Magnetic Tunnel Junction Spin Orbit Torque Devices and Circuits for In-Memory Computing|Mahshid Alamdar,Thomas Leonard,Can Cui,Bishweshwor P. Rimal,Lin Xue,Otitoaleke G. Akinola,T. Patrick Xiao,Joseph S. Friedman,Christopher H. Bennett,Matthew J. Marinella,Jean Anne C. Incorvia###

Domain Wall-Magnetic Tunnel Junction Spin Orbit Torque Devices and Circuits for In-Memory Computing. There are pressing problems with traditional computing, especially for
accomplishing data-intensive and real-time tasks, that motivate the development
of in-memory computing devices to both store information and perform
computation. Magnetic tunnel junction (MTJ) memory elements can be used for
computation by manipulating a domain wall (DW), a transition region between
magnetic domains. But, these devices have suffered from challenges: spin
transfer torque (STT) switching of a DW requires high current, and the multiple
etch steps needed to create an MTJ pillar on top of a DW track has led to
reduced tunnel magnetoresistance (TMR). These issues have limited experimental
study of devices and circuits. Here, we study prototypes of three-terminal
domain wall-magnetic tunnel junction (DW-MTJ) in-memory computing devices that
can address data processing bottlenecks and resolve these challenges by using
perpendicular magnetic anisotropy (PMA), spin-orbit torque (SOT) switching, and
an optimized lithography process to produce average device tunnel
magnetoresistance TMR = 164%, resistance-area product RA = 31
{\Omega}-{\mu}m^2, close to the RA of the unpatterned film, and lower switching
current density compared to using spin transfer torque. A two-device circuit
shows bit propagation between devices. Device initialization variation in
switching voltage is shown to be curtailed to 7% by controlling the DW initial
position, which we show corresponds to 96% accuracy in a DW-MTJ full adder
simulation. These results make strides in using MTJs and DWs for in-memory and
neuromorphic computing applications.

###Tunneling magnetoresistance enhancement by symmetrization in spin-orbit torque magnetic tunnel junction|Jiaqi Zhou,Weisheng Zhao,Kaihua Cao,Shouzhong Peng,Zilu Wang,Arnaud Bournel###

Tunneling magnetoresistance enhancement by symmetrization in spin-orbit torque magnetic tunnel junction. Heavy metals with strong spin-orbit coupling (SOC) have been employed to
generate spin current to control the magnetization dynamics by spin-orbit
torque (SOT). Magnetic tunnel junction based on SOT (SOT-MTJ) is a promising
application with efficient writing operation. Unfortunately, SOT-MTJ faces the
low tunneling magnetoresistance (TMR) problem. In this work, we present an ab
initio calculation on the TMR in SOT-MTJ. It is demonstrated that TMR would be
enhanced by SOT-MTJ symmetry structure. The symmetrization induces interfacial
resonant states (IRSs). When IRSs match identical resonances at the opposite
barrier interface, resonant tunneling occurs in SOT-MTJ, which significantly
contributes to the conductance in parallel configuration and improves TMR. We
demonstrate the occurrence of resonant tunneling by transmission spectra,
density of scattering states and differential density of states. We also point
out that the thickness of heavy metal has limited influence on TMR. This work
would benefit the TMR optimization in SOT-MTJ, as well as the SOT spintronics
device.

###Effect of resistance feedback on spin torque-induced switching of nanomagnets|Samir Garzon,Richard A. Webb,Mark Covington,Shehzaad Kaka,Thomas M. Crawford###

Effect of resistance feedback on spin torque-induced switching of nanomagnets. In large magnetoresistance devices spin torque-induced changes in resistance
can produce GHz current and voltage oscillations which can affect magnetization
reversal. In addition, capacitive shunting in large resistance devices can
further reduce the current, adversely affecting spin torque switching. Here, we
simultaneously solve the Landau-Lifshitz-Gilbert equation with spin torque and
the transmission line telegrapher's equations to study the effects of
resistance feedback and capacitance on magnetization reversal of both spin
valves and magnetic tunnel junctions. While for spin valves parallel (P) to
anti-parallel (AP) switching is adversely affected by the resistance feedback
due to saturation of the spin torque, in low resistance magnetic tunnel
junctions P-AP switching is enhanced. We study the effect of resistance
feedback on the switching time of MTJ's, and show that magnetization switching
is only affected by capacitive shunting in the pF range.

###First-principles prediction of high Curie temperature for ferromagnetic bcc-Co and bcc-FeCo alloys and its relevance to tunneling magnetoresistance|Marjana Lezaic,Phivos Mavropoulos,Stefan Blügel###

First-principles prediction of high Curie temperature for ferromagnetic bcc-Co and bcc-FeCo alloys and its relevance to tunneling magnetoresistance. We determine from first-principles the Curie temperature Tc for bulk Co in
the hcp, fcc, bcc, and tetragonalized bct phases, for FeCo alloys, and for bcc
and bct Fe. For bcc-Co, Tc=1420 K is predicted. This would be the highest Curie
temperature among the Co phases, suggesting that bcc-Co/MgO/bcc-Co tunnel
junctions offer high magnetoresistance ratios even at room temperature. The
Curie temperatures are calculated by mapping ab initio results to a Heisenberg
model, which is solved by a Monte Carlo method.

###Resonant tunneling magnetoresistance in epitaxial metal-semiconductor heterostructures|J. Varalda,A. J. A. de Oliveira,D. H. Mosca,J. -M. George,M. Eddrief,M. Marangolo,V. H. Etgens###

Resonant tunneling magnetoresistance in epitaxial metal-semiconductor heterostructures. We report on resonant tunneling magnetoresistance via localized states
through a ZnSe semiconducting barrier which can reverse the sign of the
effective spin polarization of tunneling electrons. Experiments performed on
Fe/ZnSe/Fe planar junctions have shown that positive, negative or even its
sign-reversible magnetoresistance can be obtained, depending on the bias
voltage, the energy of localized states in the ZnSe barrier and spatial
symmetry. The averaging of conduction over all localized states in a junction
under resonant condition is strongly detrimental to the magnetoresistance.

###Response of a spin valve to a spin battery|Khuôn-Viêt Pham###

Response of a spin valve to a spin battery. It is shown that spin valves under suitable symmetry conditions exhibit an
ON-OFF response to a spin battery, and are therefore perfect spin transistors.
While a spin valve driven by a charge battery displays the usual GMR (Giant
Magneto-Resistance), this means that a pure spin current or pure spin
accumulation can generate an infinite magnetoresistance (IMR). Magnetic tunnel
junctions as well as CPP (current perpendicular to plane) or CIP (current in
plane) metallic trilayers are discussed.

###Conductance in Co/Al2O3/Si/Al2O3 permalloy with asymmetrically doped barrier|R. Guerrero,F. G. Aliev,R. Villar,T. Santos,J. Moodera,V. K. Dugaev,J. Barnas###

Conductance in Co/Al2O3/Si/Al2O3 permalloy with asymmetrically doped barrier. Permalloy magnetic tunnel junctions. Complementary low frequency noise
measurements are used to understand the conductance results. The obtained data
indicate the breakdown of the Coulomb blockade for thickness of the asymmetric
silicon layer exceeding 1.2\AA . The crossover in the conductance, the
dependence of the tunnelling magnetoresistance with the bias voltage and the
noise below 80K correspond to 1 monolayer coverage. Interestingly, the zero
bias magnetoresistance remains nearly unaffected by the presence of the silicon
layer. The proposed model uses Larkin-Matveev approximation of tunnelling
through a single impurity layer generalized to 3D and takes into account the
variation of the barrier shape with the bias voltage. The main difference is
the localization of all the impurity levels within a single atomic layer. In
the high thickness case, up to 1.8\AA, we have introduced a phenomenological
parameter, which reflects the number of single levels on the total density of
silicon atoms.

###The Kondo effect in magnetic impurities and ferromagnetic contacts|Hyunsoo Yang,See-Hun Yang,Grzegorz Ilnicki,Jan Martinek,Stuart S. P. Parkin###

The Kondo effect in magnetic impurities and ferromagnetic contacts. Planar macroscopic magnetic tunnel junctions exhibit well defined zero bias
anomalies when a thin layer of ferromagnetic CoFe(B) nanodots is inserted
within a MgO based tunnel barrier. The conductance curves exhibit a single and
a double peak, respectively, for anti-parallel and parallel alignment of the
magnetizations of the electrodes which sandwich the tunnel barrier. This leads
to a suppression of the tunneling magnetoresistance near zero bias. We show
that the double peak structure indicates that the zero-bias anomaly is
spin-split due to a magnetic exchange interaction between the magnetic nanodots
and the ferromagnetic electrodes. Using a model based on an Anderson quantum
dot coupled to ferromagnetic leads, we show that these results imply the
coexistence of a Kondo effect and ferromagnetism.

###Micromagnetic study of electrical-field-assisted magnetization switching in MTJ devices|M. Carpentieri,R. Tomasello,M. Ricci,P. Burrascano,G. Finocchio###

Micromagnetic study of electrical-field-assisted magnetization switching in MTJ devices. Perpendicular MgO-based Magnetic Tunnel Junctions are optimal candidates as
building block of Spin Transfer Torque (STT) magnetoresistive memories.
However, up to now, the only STT is not enough to achieve switching current
density below 106 A/cm2. A recent work [Wang et al., Nature Mater., vol. 11, pp
64-68, Jan. 2012] has experimentally demonstrated the possibility to perform
magnetization switching assisted by an electric-field at ultra-low current
density. Theoretically, this switching has been studied by using a macrospin
approach only. Here, we show a full micromagnetic study. We found that the
switching occurs via a complex nucleation process including the nucleation of
magnetic vortexes.

###Spin-transfer dynamics in MgO-based magnetic tunnel junctions with an out-of-plane magnetized free layer and an in-plane polarizer|Ewa Kowalska,Volker Sluka,Attila Kákay,Ciarán Fowley,Jürgen Lindner,Jürgen Fassbender,Alina M. Deac###

Spin-transfer dynamics in MgO-based magnetic tunnel junctions with an out-of-plane magnetized free layer and an in-plane polarizer. Here, we present an analytical and numerical model describing the
magnetization dynamics in MgO-based spin-torque nano-oscillators with an
in-plane magnetized polarizer and an out-of-plane free layer. We introduce the
spin-transfer torque asymmetry by considering the cosine angular dependence of
the resistance between the two magnetic layers in the stack. For the analytical
solution, dynamics are determined by assuming a circular precession trajectory
around the direction perpendicular to the plane, as set by the effective field,
and calculating the energy integral over a single precession period. In a more
realistic approach, we include the bias dependence of the tunnel
magnetoresistance, which is assumed empirically to be a piecewise linear
function of the applied voltage. The dynamical states are found by solving the
stability condition for the Jacobian matrix for out-of-plane static states. We
find that the bias dependence of the tunnel magnetoresistance, which is an
inseparable effect in every tunnel junction, exhibits drastic impact on the
spin-torque nano-oscillator phase diagram, mainly by increasing the critical
current for dynamics and quenching the oscillations at high currents. The
results are in good agreement with our experimental data published elsewhere.

###Quantum Oscillations of Tunnel Magnetoresistance Induced by Spin-Wave Excitations in Ferromagnet-Ferromagnet-Ferromagnet Double Barrier Tunnel Junctions|Xi Chen,Qing-Rong Zheng,Gang Su###

Quantum Oscillations of Tunnel Magnetoresistance Induced by Spin-Wave Excitations in Ferromagnet-Ferromagnet-Ferromagnet Double Barrier Tunnel Junctions. The possibility of quantum oscillations of the tunnel conductance and
magnetoresistance induced by spin-wave excitations in a
ferromagnet-ferromagnet-ferromagnet double barrier tunnel junction, when the
magnetizations of the two side ferromagnets are aligned antiparallel to that of
the middle ferromagnet, is investigated in a self-consistent manner by means of
Keldysh nonequilibrium Green function method. It has been found that owing to
the s-d exchange interactions between conduction electrons and the spin density
induced by spin accumulation in the middle ferromagnet, the differential
conductance and the TMR indeed oscillate with the increase of bias voltage,
being consistent with the phenomenon that is observed recently in experiments.
The effects of magnon modes, the energy levels of electrons as well as the
molecular field in the central ferromagnet on the oscillatory transport
property of the system are also discussed.

###Enhanced all-optical switching and domain wall velocity in annealed synthetic-ferrimagnetic multilayers|Luding Wang,Youri L. W. van Hees,Reinoud Lavrijsen,Weisheng Zhao,Bert Koopmans###

Enhanced all-optical switching and domain wall velocity in annealed synthetic-ferrimagnetic multilayers. All optical switching (AOS) of the magnetization in synthetic ferrimagnetic
Pt/Co/Gd stacks has received considerable interest due to its high potential
towards integration with spintronic devices, such as magnetic tunnel junctions
(MTJs), to enable ultrafast memory applications. Post-annealing is an essential
process in the MTJ fabrication to obtain optimized tunnel magnetoresistance
(TMR) ratio. However, with integrating AOS with an MTJ in prospect, the
annealing effects on single-pulse AOS and domain wall (DW) dynamics in the
Pt/Co/Gd stacks haven't been systematically investigated yet. In this study, we
experimentally explore the annealing effect on AOS and field-induced DW motion
in Pt/Co/Gd stacks. The results show that the threshold fluence (F_0) for AOS
is reduced significantly as a function of annealing temperature (T_a) ranging
from 100C to 300C. Specifically, a 28% reduction of F_0 can be observed upon
annealing at 300C, which is a critical T_a for MTJ fabrication. Lastly, we also
demonstrate a significant increase of the DW velocity in the creep regime upon
annealing, which is attributed to annealing-induced Co/Gd interface
intermixing. Our findings show that annealed Pt/Co/Gd system facilitates
ultrafast and energy-efficient AOS, as well as enhanced DW velocity, which is
highly suitable towards opto-spintronic memory applications.

###Ab initio Prediction of Mechanical, Electronic, Magnetic and Transport Properties of Bulk and Heterostructure of a Novel Fe-Cr based Full Heusler Chalcogenide|Joydipto Bhattacharya,Rajeev Dutt,Aparna Chakrabarti###

Ab initio Prediction of Mechanical, Electronic, Magnetic and Transport Properties of Bulk and Heterostructure of a Novel Fe-Cr based Full Heusler Chalcogenide. Using electronic structure calculations based on density functional theory,
we predict and study the structural, mechanical, electronic, magnetic and
transport properties of a new full Heusler chalcogenide, namely, Fe$_2$CrTe,
both in bulk and heterostructure form. The system shows a ferromagnetic and
half-metallic(HM) like behavior, with a very high (about 95%) spin polarization
at the Fermi level, in its cubic phase. Interestingly, under tetragonal
distortion, a clear minimum (with almost the same energy as the cubic phase)
has also been found, at a c/a value of 1.26, which, however, shows a
ferrimagnetic and fully metallic nature. The compound has been found to be
dynamically stable in both the phases against the lattice vibration. The
elastic properties indicate that the compound is mechanically stable in both
the phases, following the stability criteria of the cubic and tetragonal
phases. The elastic parameters unveil the mechanically anisotropic and ductile
nature of the alloy system. Due to the HM-like behavior of the cubic phase and
keeping in mind the practical aspects, we probe the effect of strain as well as
substrate on various physical properties of this alloy. Transmission profile of
the Fe$_2$CrTe/MgO/Fe$_2$CrTe heterojunction has been calculated to probe it as
a magnetic tunneling junction (MTJ) material in both the cubic and tetragonal
phases. Considerably large tunneling magnetoresistance ratio (TMR) of 1000% is
observed for the tetragonal phase, which is found to be one order of magnitude
larger than that of the cubic phase.

###Spin Hall Induced Magnetization Dynamics in Multiferroic Tunnel Junction|Jakub Pawlak,Witold Skowroński,Piotr Kuświk,Félix Casanova,Marek Przybylski###

Spin Hall Induced Magnetization Dynamics in Multiferroic Tunnel Junction. The combination of spin-orbit coupling driven effects and multiferroic
tunneling properties was explored experimentally in thin Pt/Co/BTO/LSMO
multilayers. The presence of a Pt heavy metal allows for the spin
current-induced magnetization precession of Co upon radio-frequency charge
current injection. The utilization of a BTO ferroelectric tunnel barrier
separating the Co and LSMO ferromagnetic electrodes gives rise to both
tunneling-magnetoresistance and electroresistance. Using the spin-orbit torque
ferromagnetic resonance, the maganetization dynamics of the Co/Pt bilayers was
studied at room temperature. Unexpectedly the magnetization dynamics study in
the same geometry performed at low temperature reveals the existence of both Co
and LSMO resonance peaks indicating efficient spin current generation both
using the spin Hall effect in Pt and spin pumping in LSMO that tunnel via the
BTO barrier.

###Resonant Spin-Dependent Tunneling in Spin-Valve Junctions in the Presence of Paramagnetic Impurities|A. Vedyayev,D. Bagrets,A. Bagrets,B. Dieny###

Resonant Spin-Dependent Tunneling in Spin-Valve Junctions in the Presence of Paramagnetic Impurities. The tunnel magnetoresistance (TMR) of F/O/F magnetic junctions, (F's are
ferromagnetic layers and O is an oxide spacer) in the presence of magnetic
impurities within the barrier, is investigated. We assume that magnetic
couplings exist both between the spin of impurity and the bulk magnetization of
the neighboring magnetic electrode, and between the spin of impurity and the
spin of tunneling electron. Consequently, the resonance levels of the system
formed by a tunneling electron and a paramagnetic impurity with spin S=1, are a
sextet. As a result the resonant tunneling depends on the direction of the
tunneling electron spin. At low temperatures and zero bias voltage the TMR of
the considered system may be larger than TMR of the same structure without
paramagnetic impurities. It is calculated that an increase in temperature leads
to a decrease in the TMR amplitude due to excitation of spin-flip processes
resulting in mixing of spin up and down channels. It is also shown that
asymmetry in the location of the impurities within the barrier can lead to
asymmetry in $I(V)$ characteristics of impurity assisted current and two
mechanisms responsible for the origin of this effect are established. The first
one is due to the excitation of spin-flip processes at low voltages and the
second one arises from the shift of resonant levels inside the insulator layer
under high applied voltages.

###Magnetic-Field-Modulated Resonant Tunneling in Ferromagnetic-Insulator-Nonmagnetic junctions|Yang Song,Hanan Dery###

Magnetic-Field-Modulated Resonant Tunneling in Ferromagnetic-Insulator-Nonmagnetic junctions. We present a theory for resonance-tunneling magnetoresistance (MR) in
Ferromagnetic-Insulator-Nonmagnetic junctions. The theory sheds light on many
of the recent electrical spin injection experiments, suggesting that this MR
effect rather than spin accumulation in the nonmagnetic channel corresponds to
the electrically detected signal. We quantify the dependence of the tunnel
current on the magnetic field by quantum rate equations derived from the
Anderson impurity model, with important addition of impurity spin interactions.
Considering the on-site Coulomb correlation, the MR effect is caused by
competition between the field, spin interactions and coupling to the magnetic
lead. By extending the theory, we present a basis for operation of novel
nm-size memories.

###Large nonvolatile control of magnetic anisotropy in CoPt by a ferroelectric ZnO-based tunneling barrier|Muftah Al-Mahdawi,Mohamed Belmoubarik,Masao Obata,Daiki Yoshikawa,Hideyuki Sato,Tomohiro Nozaki,Tatsuki Oda,Masashi Sahashi###

Large nonvolatile control of magnetic anisotropy in CoPt by a ferroelectric ZnO-based tunneling barrier. The electric control of magnetic anisotropy has important applications for
nonvolatile memory and information processing. By first-principles
calculations, we show a large nonvolatile control of magnetic anisotropy in
ferromagnetic/ferroelectric CoPt/ZnO interface. Using the switched electric
polarization of ZnO, the density-of-states and magnetic anisotropy at the CoPt
surface show a large change. Due to a strong Co/Pt orbitals hybridization and a
large spin-orbit coupling, a large control of magnetic anisotropy was found. We
experimentally measured the change of effective anisotropy by tunneling
resistance measurements in CoPt/Mg-doped ZnO/Co junctions. Additionally, we
corroborate the origin of the control of magnetic anisotropy by observations on
tunneling anisotropic magnetoresistance.

###Emergent Spin-Filter at the interface between Ferromagnetic and Insulating Layered Oxides|Yaohua Liu,F. A. Cuellar,Z. Sefrioui,J. W. Freeland,M. R. Fitzsimmons,C. Leon,J. Santamaria,S. G. E. te Velthuis###

Emergent Spin-Filter at the interface between Ferromagnetic and Insulating Layered Oxides. We report a strong effect of interface-induced magnetization on the transport
properties of magnetic tunnel junctions consisting of ferromagnetic manganite
La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ and insulating cuprate PrBa$_{2}$Cu$_{3}$O$_{7}$.
Contrary to the typically observed steady increase of the tunnel
magnetoresistance with decreasing temperature, this system exhibits a sudden
anomalous decrease at low temperatures. Interestingly, this anomalous behavior
can be attributed to the competition between the positive spin polarization of
the manganite contacts and the negative spin-filter effect from the
interface-induced Cu magnetization.

###Reduction of spin polarization by incoherent tunneling in Co2FeAl/MgO/CoFe magnetic tunnel junctions with thick MgO barriers|M. S. Gabor,C. Tiusan,T. Petrisor Jr,T. Petrisor,M. Hehn,Y. Lu,E. Snoeck###

Reduction of spin polarization by incoherent tunneling in Co2FeAl/MgO/CoFe magnetic tunnel junctions with thick MgO barriers. We report on spin polarization reduction by incoherent tunneling in realistic
single crystal Co2FeAl/MgO/Co50Fe50 magnetic tunnel junctions (MTJ) compared to
reference Fe/MgO/Fe. A large density of misfit dislocations in the Heusler
based MTJs has been insured by a thick MgO barrier and its 3.8% lattice
mismatch with the Co2FeAl electrode. Our analysis implicates a correlated
structural-transport approach. The crystallographic coherence, in the real
space, is investigated using High Resolution Transmission Electron Microscopy
phase analysis. The electronic transport experiments in variable temperature,
fitted with a theoretical extended-Glazman-Matveev model, address different
levels of the tunneling mechanisms from direct to multi-center hopping. We
demonstrate a double negative impact of dislocations, as extended defects, on
the tunneling polarization. Firstly, the breaking of the crystal symmetry
destroys the longitudinal and lateral coherence of the propagating Bloch
functions. This affects the symmetry filtering efficiency of the Delta_1 states
across the (100) MgO barriers and reduces the associated effective tunneling
polarization. Secondly, dislocations provide localized states within the MgO
gap. This determines temperature activated spin-conserving inelastic tunneling
through chains of defects which are responsible for the one order of magnitude
drop of the tunnel magnetoresistance from low to room temperature.

###First-principles study of Co concentration and interfacial resonance states in Fe$_{1-x}$Co$_x$ magnetic tunnel junctions|Jonathan Trinastic,Yan Wang,Hai-Ping Cheng###

First-principles study of Co concentration and interfacial resonance states in Fe$_{1-x}$Co$_x$ magnetic tunnel junctions. The optimal Co concentration in Fe$_{1-x}$Co$_{x}$/MgO magnetic tunnel
junctions (MTJs) that maximizes tunneling magnetoresistance (TMR) is still
under investigation. We perform a first-principles transport study on MTJs
using disordered electrodes modeled using the virtual crystal approximation
(VCA) and ordered alloys with various MgO barrier thicknesses. We find that
10-20$%$ Co concentration maximizes TMR using VCA to represent disorder in the
electrodes. This TMR peak arises due to a minority d-type interfacial resonance
state (IRS) that becomes filled with small Co doping, leading to a decrease in
antiparallel conductance. Calculations with ordered Fe$_{1-x}$Co$_{x}$
electrodes confirm the filling of this minority d-type IRS for small Co
concentrations. In addition, we construct a 10x10 supercell without VCA to
explicitly represent disorder at the Fe$_{1-x}$Co$_x$/MgO interface, which
demonstrates a quenching of the minority-d IRS and significant reduction in
available states at the Fermi level that agrees with VCA calculations. These
results explain recent experimental findings and provide implications for the
impact of IRS on conductance and TMR in Fe$_{1-x}$Co$_x$/MgO tunnel junctions.

###Tunable magnetoresistance in spin-orbit coupled graphene junctions|Razieh Beiranvand,Hossein Hamzehpour###

Tunable magnetoresistance in spin-orbit coupled graphene junctions. Using the Landauer-B\"utikker formalism, we study the graphene
magneto-transport in the presence of Rashba spin-orbit interaction (RSOI). We
show that the angle resolved transmission probability in the proposed
structures can be tuned by the RSOI strength. The transmission spectrum show
Klein tunneling in the parallel (P) magnetization configuration which can be
blocked by the RSOI. This effect is also observable for the anti-parallel (AP)
magnetization configuration in different incident angle. The numerical results
shows that the spin-polarized conductance strongly depends on the strength of
the RSOI and can be generated by tuning the magnetic exchange field and RSOI
strength. This spin-polarized conductance is a sensitive oscillatory function
of the thickness of the RSO region. Because of the spin-flip effect, the
junction shows a spin-valve effect with large and negative magnetoresistance
(MR) and spin-magnetoresistance (SMR) in the presence of RSOI. When the RSOI is
on, the frequency and amplitude of shot-noise and Fano factor's oscillations
are also increased. These results can provide a way to extending the
application of graphene-based junctions in spintronics.

###Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces|Thach D. N. Ngo,Jung-Won Chang,Kyujoon Lee,Seungju Han,Joon Sung Lee,Young Heon Kim,Myung-Hwa Jung,Yong-Joo Doh,Mahn-Soo Choi,Jonghyun Song,Jinhee Kim###

Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces. Complex oxide systems have attracted considerable attention because of their
fascinating properties, including the magnetic ordering at the conducting
interface between two band insulators, such as LaAlO3 (LAO) and SrTiO3 (STO).
However, the manipulation of the spin degree of freedom at the LAO/STO
heterointerface has remained elusive. Here, we have fabricated hybrid magnetic
tunnel junctions consisting of Co and LAO/STO ferromagnets with the insertion
of a Ti layer in between, which clearly exhibit magnetic switching and the
tunnelling magnetoresistance (TMR) effect below 10 K. The magnitude and the of
the TMR are strongly dependent on the direction of the rotational magnetic
field parallel to the LAO/STO plane, which is attributed to a strong
Rashba-type spin orbit coupling in the LAO/STO heterostructure. Our study
provides a further support for the existence of the macroscopic ferromagnetism
at LAO/STO heterointerfaces and opens a novel route to realize interfacial
spintronics devices.

###Optical Switching in Tb/Co-Multilayer Based Nanoscale Magnetic Tunnel Junctions|Sucheta Mondal,Debanjan Polley,Akshay Pattabi,Jyotirmoy Chatterjee,David Salomoni,Luis Aviles-Felix,Aurélien Olivier,Miguel Rubio-Roy,Bernard Diény,Liliana Daniela Buda Prejbeanu,Ricardo Sousa,Ioan Lucian Prejbeanu,Jeffrey Bokor###

Optical Switching in Tb/Co-Multilayer Based Nanoscale Magnetic Tunnel Junctions. Magnetic tunnel junctions (MTJs) are elementary units of magnetic memory
devices. For high-speed and low-power data storage and processing applications,
fast reversal by an ultrashort laser pulse is extremely important. We
demonstrate optical switching of Tb/Comultilayer-based nanoscale MTJs by
combining optical writing and electrical read-out methods. A 90 fs-long laser
pulse switches the magnetization of the storage layer (SL). The change in
magnetoresistance between the SL and a reference layer (RL) is probed
electrically across the tunnel barrier. Single-shot switching is demonstrated
by varying the cell diameter from 300 nm to 20 nm. The anisotropy,
magnetostatic coupling, and switching probability exhibit cell-size dependence.
By suitable association of laser fluence and magnetic field, successive
commutation between high-resistance and low-resistance states is achieved. The
switching dynamics in a continuous film is probed with the magneto-optical Kerr
effect technique. Our experimental findings provide strong support for the
growing interest in ultrafast spintronic devices.

###Tunneling Magnetoresistance in Noncollinear Antiferromagnetic Tunnel Junctions|Jianting Dong,Xinlu Li,Gautam Gurung,Meng Zhu,Peina Zhang,Fanxing Zheng,Evgeny Y. Tsymbal,Jia Zhang###

Tunneling Magnetoresistance in Noncollinear Antiferromagnetic Tunnel Junctions. Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics
driven by the advantages of antiferromagnets producing no stray fields and
exhibiting ultrafast magnetization dynamics. The efficient method to detect an
AFM order parameter, known as the N\'eel vector, by electric means is critical
to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear
AFM metals, such as Mn3Sn, exhibit a momentum dependent spin polarization which
can be exploited in AFM tunnel junctions to detect the N\'eel vector. Using
first-principles calculations based on density functional theory, we predict a
tunneling magnetoresistance (TMR) effect as high as 300% in AFM tunnel
junctions with Mn3Sn electrodes, where the junction resistance depends on the
relative orientation of their N\'eel vectors and exhibits four non-volatile
resistance states. We argue that the spin-split band structure and the related
TMR effect can also be realized in other non-collinear AFM metals like Mn3Ge,
Mn3Ga, Mn3Pt, and Mn3GaN. Our work provides a robust method for detecting the
N\'eel vector in non-collinear antiferromagnets via the TMR effect, which may
be useful for their application in AFM spintronic devices.

###Giant perpendicular magnetic anisotropy enhancement in MgO-based magnetic tunnel junction by using Co/Fe composite layer|Libor Vojáček,Fatima Ibrahim,Ali Hallal,Bernard Dieny,Mairbek Chshiev###

Giant perpendicular magnetic anisotropy enhancement in MgO-based magnetic tunnel junction by using Co/Fe composite layer. Magnetic tunnel junctions with perpendicular anisotropy form the basis of the
spin-transfer torque magnetic random-access memory (STT-MRAM), which is
non-volatile, fast, dense, and has quasi-infinite write endurance and low power
consumption. Based on density functional theory (DFT) calculations, we propose
an alternative design of magnetic tunnel junctions comprising
Fe(n)Co(m)Fe(n)/MgO storage layers with greatly enhanced perpendicular magnetic
anisotropy (PMA) up to several mJ/m2, leveraging the interfacial perpendicular
anisotropy of Fe/MgO along with a stress-induced bulk PMA discovered within bcc
Co. This giant enhancement dominates the demagnetizing energy when increasing
the film thickness. The tunneling magnetoresistance (TMR) estimated from the
Julliere model is comparable with that of the pure Fe/MgO case. We discuss the
advantages and pitfalls of a real-life fabrication of the structure and propose
the Fe(3ML)Co(4ML)Fe(3ML) as a storage layer for MgO-based STT-MRAM cells. The
large PMA in strained bcc Co is explained in the framework of Bruno's model by
the MgO-imposed strain and consequent changes in the energies of dyz and dz2
minority-spin bands.

###Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of $La_{1.9}Sr_{0.1}CuO_4$ - $La_{0.67}Ca_{0.33}MnO_3$ - $La_{1.9}Sr_{0.1}CuO_4$|Gad Koren,Tal Kirzhner###

Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of $La_{1.9}Sr_{0.1}CuO_4$ - $La_{0.67}Ca_{0.33}MnO_3$ - $La_{1.9}Sr_{0.1}CuO_4$. Transport and Conductance spectra measurements of ramp-type junctions made of
cuprate superconducting $La_{1.9}Sr_{0.1}CuO_4$ electrodes and a manganite
ferromagnetic $La_{0.67}Ca_{0.33}MnO_3$ barrier are reported. At low
temperatures below $T_c$, the conductance spectra show Andreev-like broad peaks
superposed on a tunneling-like background, and sometimes also sub-gap Andreev
resonances. The energy gap values $\Delta$ found from fits of the data ranged
mostly between 7-10 mV. As usual, the gap features were suppressed under
magnetic fields but revealed the tunneling-like conductance background. After
field cycling to 5 or 6 T and back to 0 T, the conductance spectra were always
higher than under zero field cooling, reflecting the negative magnetoresistance
of the manganite barrier. A signature of superparamagnetism was found in the
conductance spectra of junctions with a 12 nm thick LCMO barrier. Observed
critical currents with barrier thickness of 12 nm or more, were shown to be an
artifact due to incomplete milling of one of the superconducting electrodes.

###Comparative analysis of tunneling magnetoresistance in low-$T_c$ Nb/AlAlOx/Nb and high-$T_c$ Bi$_{2-y}$Pb$_y$Sr$_2$CaCu$_2$O$_{8+δ}$ intrinsic Josephson junctions|V. M. Krasnov,H. Motzkau,T. Golod,A. Rydh,S. O. Katterwe,A. B. Kulakov###

Comparative analysis of tunneling magnetoresistance in low-$T_c$ Nb/AlAlOx/Nb and high-$T_c$ Bi$_{2-y}$Pb$_y$Sr$_2$CaCu$_2$O$_{8+δ}$ intrinsic Josephson junctions. We perform a detailed comparison of magnetotunneling in conventional
low-$T_c$ Nb/AlAlOx/Nb junctions with that in slightly overdoped
Bi$_{2-y}$Pb$_y$Sr$_2$CaCu$_2$O$_{8+\delta}$ [Bi(Pb)-2212] intrinsic Josephson
junctions and with microscopic calculations. It is found that both types of
junctions behave in a qualitatively similar way. Both magnetic field and
temperature suppress superconductivity in the state-conserving manner. This
leads to the characteristic sign-change of tunneling magnetoresistance from the
negative at the sub-gap to the positive at the sum-gap bias. We derived
theoretically and verified experimentally scaling laws of magnetotunneling
characteristics and employ them for accurate extraction of the upper critical
field $H_{c2}$. For Nb an extended region of surface superconductivity at
$H_{c2}<H<H_{c3}$ is observed. The parameters of Bi(Pb)-2212 were obtained from
self-consistent analysis of magnetotunneling data at different levels of bias,
dissipation powers and for different mesa sizes, which precludes the influence
of self-heating. It is found that $H_{c2}(0)$ for Bi(Pb)-2212 is $\simeq 70$ T
and decreases significantly at $T\rightarrow T_c$. The amplitude of sub-gap
magnetoresistance is suppressed exponentially at $T>T_c/2$, but remains
negative, although very small, above $T_c$. This may indicate existence of an
extended fluctuation region, which, however, does not destroy the general
second-order type of the phase transition at $T_c$.

###Large two-level magnetoresistance effect in doped manganite grain boundary junctions|J. B. Philipp,C. Hoefener,S. Thienhaus,J. Klein,L. Alff,R. Gross###

Large two-level magnetoresistance effect in doped manganite grain boundary junctions. We performed a systematic analysis of the tunneling magnetoresistance (TMR)
effect in single grain boundary junctions formed in epitaxial
La(2/3)Ca(1/3)MnO(3) films deposited on SrTiO(3) bicrystals. For magnetic
fields H applied parallel to the grain boundary barrier, an ideal two-level
resistance switching behavior with sharp transitions is observed with a TMR
effect of up to 300% at 4.2 K and still above 100% at 77 K. Varying the angle
between H and the grain boundary results in differently shaped resistance vs H
curves. The observed behavior is explained within a model of magnetic domain
pinning at the grain boundary interface.

###High magnetoresistance of hexagonal boron nitride-graphene heterostructure-based MTJ through excited-electron transmission|Halimah Harfah,Yusuf Wicaksono,Gagus Ketut Sunnardianto,Muhammad Aziz Majidi,Koichi Kusakabea###

High magnetoresistance of hexagonal boron nitride-graphene heterostructure-based MTJ through excited-electron transmission. This work presents an ab-initio study of a few-layers hexagonal boron nitride
(hBN) and hBN-graphene heterostructure sandwiched between Ni(111) layers. The
aim of this study is to understand the electron transmission process through
the interface. Spin-polarized density functional theory calculations and
transmission probability calculations were conducted on Ni(111)/$n$hBN/Ni(111)
with $n$ = 2, 3, 4, and 5 as well as on Ni(111)/hBN-Gr-hBN/Ni(111). Slabs with
magnetic alignment in an anti-parallel configuration (APC) and parallel
configuration (PC) were considered. The pd-hybridizations at both the upper and
lower interfaces between the Ni slabs and hBN were found to stabilize the
system. The Ni/nhBN/Ni magnetic tunnel junction (MTJ) was found to exhibit a
high tunneling magnetoresistance (TMR) ratio at ~0.28 eV for $n$ = 2 and 0.34
eV for $n$ > 2, which are slightly higher than the Fermi energy. The observed
shifting of this high TMR ratio originates from the transmission of electrons
through the surface states of the $d_{z^2}$-orbital of Ni atoms at interfaces
which are hybridized with the $p_z$-orbital of N atoms. In the case of $n$ > 2,
the proximity effect causes an evanescent wave, contributing to decreasing
transmission probability but increasing the TMR ratio. However, TMR ratio, as
well as transmission probability, was found to be increased, by replacing the
unhybridized hBN layer of the Ni/3hBN/Ni MTJ with graphene, thus becoming
Ni/hBN-Gr-hBN/Ni. A TMR ratio as high as ~1200% was observed at an energy of
0.34 eV, which is higher than the Fermi energy. Furthermore, a design is
proposed for a device based on a new reading mechanism using the high TMR
observed just above the Fermi energy level.

###Large and tunable magnetoresistance in van der Waals Ferromagnet/Semiconductor junctions|Wenkai Zhu,Yingmei Zhu,Tong Zhou,Xianpeng Zhang,Hailong Lin,Qirui Cui,Faguang Yan,Ziao Wang,Yongcheng Deng,Hongxin Yang,Lixia Zhao,Igor Žutić,Kirill D. Belashchenko,Kaiyou Wang###

Large and tunable magnetoresistance in van der Waals Ferromagnet/Semiconductor junctions. Magnetic tunnel junctions (MTJs) with conventional bulk ferromagnets
separated by a nonmagnetic insulating layer are key building blocks in
spintronics for magnetic sensors and memory. A radically different approach of
using atomically-thin van der Waals (vdW) materials in MTJs is expected to
boost their figure of merit, the tunneling magnetoresistance (TMR), while
relaxing the lattice-matching requirements from the epitaxial growth and
supporting high-quality integration of dissimilar materials with
atomically-sharp interfaces. We report TMR up to 192% at 10 K in all-vdW
Fe3GeTe2/GaSe/Fe3GeTe2 MTJs. Remarkably, instead of the usual insulating
spacer, this large TMR is realized with a vdW semiconductor GaSe. Integration
of two-dimensional ferromagnets in semiconductor-based vdW junctions offers
gate-tunability, bias dependence, magnetic proximity effects, and
spin-dependent optical-selection rules. We demonstrate that not just the
magnitude, but also the TMR sign is tuned by the applied bias or the
semiconductor thickness, enabling modulation of highly spin-polarized carriers
in vdW semiconductors.

###Unravelling the role of the interface for spin injection into organic semiconductors|Clément Barraud,Pierre Seneor,Richard Mattana,Stéphane Fusil,Karim Bouzehouane,Cyrile Deranlot,Patrizio Graziosi,Luis Hueso,Ilaria Bergenti,Valentin Dediu,Frédéric Petroff,Albert Fert###

Unravelling the role of the interface for spin injection into organic semiconductors. Whereas spintronics brings the spin degree of freedom to electronic devices,
molecular/organic electronics adds the opportunity to play with the chemical
versatility. Here we show how, as a contender to commonly used inorganic
materials, organic/molecular based spintronics devices can exhibit very large
magnetoresistance and lead to tailored spin polarizations. We report on giant
tunnel magnetoresistance of up to 300% in a (La,Sr)MnO3/Alq3/Co nanometer size
magnetic tunnel junction. Moreover, we propose a spin dependent transport model
giving a new understanding of spin injection into organic materials/molecules.
Our findings bring a new insight on how one could tune spin injection by
molecular engineering and paves the way to chemical tailoring of the properties
of spintronics devices.

###Magnetoresistive sensors based on the elasticity of domain walls|Xueying Zhang,Nicolas Vernier,Zhiqiang Cao,Qunwen Leng,Anni Cao,Dafine Ravelosona,Weisheng Zhao###

Magnetoresistive sensors based on the elasticity of domain walls. Magnetic sensors based on the magnetoresistance effects have a promising
application prospect due to their excellent sensitivity and advantages in terms
of the integration. However, competition between higher sensitivity and larger
measuring range remains a problem. Here, we propose a novel mechanism for the
design of magnetoresistive sensors: probing the perpendicular field by
detecting the expansion of the elastic magnetic Domain Wall (DW) in the free
layer of a spin valve or a magnetic tunnel junction. Performances of devices
based on this mechanism, such as the sensitivity and the measuring range can be
tuned by manipulating the geometry of the device, without changing the
intrinsic properties of the material, thus promising a higher integration level
and a better performance. The mechanism is theoretically explained based on the
experimental results. Two examples are proposed and their functionality and
performances are verified via micromagnetic simulation.

###Spin-dependent transport in van der Waals magnetic tunnel junctions with Fe3GeTe2 electrodes|Xinlu Li,Evgeny Y. Tsymbal,Jing-Tao Lü,Jia Zhang,Long You,Yurong Su###

Spin-dependent transport in van der Waals magnetic tunnel junctions with Fe3GeTe2 electrodes. Van der Waals (vdW) heterostructures, stacking different two-dimensional
materials, have opened up unprecedented opportunities to explore new physics
and device concepts. Especially interesting are recently discovered
two-dimensional magnetic vdW materials, providing new paradigms for spintronic
applications. Here, using density functional theory (DFT) calculations, we
investigate the spin-dependent electronic transport across vdW magnetic tunnel
junctions (MTJs) composed of Fe3GeTe2 ferromagnetic electrodes and a graphene
or hexagonal boron nitride (h-BN) spacer layer. For both types of junctions, we
find that the junction resistance changes by thousands of percent when the
magnetization of the electrodes is switched from parallel to antiparallel. Such
a giant tunneling magnetoresistance (TMR) effect is driven by dissimilar
electronic structure of the two spin-conducting channels in Fe3GeTe2, resulting
in a mismatch between the incoming and outgoing Bloch states in the electrodes
and thus suppressed transmission for an antiparallel-aligned MTJ. The vdW
bounding between electrodes and a spacer layer makes this result virtually
independent of the type of the spacer layer, making the predicted giant TMR
effect robust with respect to strain, lattice mismatch, interface distance and
other parameters which may vary in the experiment. We hope that our results
will further stimulate experimental studies of vdW MTJs and pave the way for
their applications in spintronics.

###First- and Second-Order Phase Transitions, Fulde-Ferrel Inhomogeneous State and Quantum Criticality in Ferromagnet/Superconductor Double Tunnel Junctions|Biao Jin,Gang Su,Qing-Rong Zheng###

First- and Second-Order Phase Transitions, Fulde-Ferrel Inhomogeneous State and Quantum Criticality in Ferromagnet/Superconductor Double Tunnel Junctions. First- and second-order phase transitions, Fulde-Ferrel (FF) inhomogeneous
superconducting (SC) state and quantum criticality in
ferromagnet/superconductor/ferromagnet double tunnel junctions are
investigated. For the antiparallel alignment of magnetizations, it is shown
that a first-order phase transition from the homogeneous BCS state to the
inhomogeneous FF state occurs at a certain bias voltage $V^{\ast}$; while the
transitions from the BCS state and the FF state to the normal state at $%
V_{c}$ are of the second-order. A phase diagram for the central superconductor
is presented. In addition, a quantum critical point (QCP), $% V_{QCP}$, is
identified. It is uncovered that near the QCP, the SC gap, the chemical
potential shift induced by the spin accumulation, and the difference of free
energies between the SC and normal states vanish as $% |V-V_{QCP}|^{z\nu}$ with
the quantum critical exponents $z\nu =1/2$, 1 and 2, respectively. The tunnel
conductance and magnetoresistance are also discussed.

###Epitaxial Co2Cr0.6Fe0.4Al thin films and magnetic tunneling junctions|A. Conca,M. Jourdan,H. Adrian###

Epitaxial Co2Cr0.6Fe0.4Al thin films and magnetic tunneling junctions. Epitaxial thin films of the theoretically predicted half metal
Co2Cr0.6Fe0.4Al were deposited by dc magnetron sputtering on different
substrates and buffer layers. The samples were characterized by x-ray and
electron beam diffraction (RHEED) demonstrating the B2 order of the Heusler
compound with only a small partition of disorder on the Co sites. Magnetic
tunneling junctions with Co2Cr0.6Fe0.4Al electrode, AlOx barrier and Co counter
electrode were prepared. From the Julliere model a spin polarisation of
Co2Cr0.6Fe0.4Al of 54% at T=4K is deduced. The relation between the annealing
temperature of the Heusler electrodes and the magnitude of the tunneling
magnetoresistance effect was investigated and the results are discussed in the
framework of morphology and surface order based of in situ STM and RHEED
investigations.

###Effects of Elastic Dephasing on Scaling of ultra-small Magnetic Tunnel Junctions|Debasis Das,Ashwin Tulapurkar,Bhaskaran Muralidharan###

Effects of Elastic Dephasing on Scaling of ultra-small Magnetic Tunnel Junctions. The study of the effects of scaling on magnetic tunnel junction (MTJ) devices
has become an important topic in the field of spin-based memory devices. Here,
we investigate the effect of elastic dephasing on trilayer and pentalayer MTJ
considered at small transverse cross-sectional areas using the non-equilibrium
Green's function spin transport formalism. We consider the structures with and
without dephasing effects and clearly point out as to how the tunnel
magnetoresistance effect gets affected by dephasing. We attribute the trends
noted by analyzing the transmission spectra and hence the currents across the
devices. Although dephasing affects the TMR values for both devices, we note
that the obtained TMR values are still in a reasonable range that may not
hinder their usability for practical applications.

###Flexible MgO barrier magnetic tunnel junctions|Li Ming Loong,Wonho Lee,Xuepeng Qiu,Ping Yang,Hiroyo Kawai,Mark Saeys,Jong-Hyun Ahn,Hyunsoo Yang###

Flexible MgO barrier magnetic tunnel junctions. Flexible electronic devices require the integration of multiple crucial
components on soft substrates to achieve their functions. In particular, memory
devices are the fundamental component for data storage and processing in
flexible electronics. Here, we present flexible MgO barrier magnetic tunnel
junction (MTJ) devices fabricated using a transfer printing process, which
exhibit reliable and stable operation under substantial deformation of the
device substrates. In addition, the flexible MTJ devices yield significantly
enhanced tunneling magnetoresistance (TMR) of ~300 % and improved abruptness of
switching, as residual strain in the MTJ structure induced by the fabrication
process is released during the transfer process. This approach could be useful
for a wide range of flexible electronic systems that require high performance
memory components.

###Giant Piezospintronic Effect in a Noncollinear Antiferromagnetic Metal|Huixin Guo,Zexin Feng,Han Yan,Jiuzhao Liu,Jia Zhang,Xiaorong Zhou,Peixin Qin,Jialin Cai,Zhongming Zeng,Xin Zhang,Xiaoning Wang,Hongyu Chen,Haojiang Wu,Chengbao Jiang,Zhiqi Liu###

Giant Piezospintronic Effect in a Noncollinear Antiferromagnetic Metal. One of the main bottleneck issues for room-temperature antiferromagnetic
spintronic devices is the small signal read-out owing to the limited
anisotropic magnetoresistance in antiferromagnets. However, this could be
overcome by either utilizing the Berry-curvature-induced anomalous Hall
resistance in noncollinear antiferromagnets or establishing tunnel junction
devices based on effective manipulation of antiferromagnetic spins. In this
work, we demonstrate the giant piezoelectric strain control of the spin
structure and the anomalous Hall resistance in a noncollinear antiferromagnetic
metal - D019 hexagonal Mn3Ga. Furthermore, we built tunnel junction devices
with a diameter of 200 nm to amplify the maximum tunneling resistance ratio to
more than 10% at room-temperature, which thus implies significant potential of
noncollinear antiferromagnets for large signal-output and high-density
antiferromagnetic spintronic device applications.

###Low Field Magnetotransport in Manganites|P. K. Siwach,H. K. Singh,O. N. Srivastava###

Low Field Magnetotransport in Manganites. The perovskite manganites of general formula RE_1-xAe_xMnO_3 (RE= rare
earth,AE=Ca, Sr, Ba and Pb)have drawn considerable attention, especially
following the discovery of colossal magnetoresistance (CMR). They exhibit
extraordinary large magnetoresistance pronounced as CMR in the vicinity of
insulator-metal/paramagnetic-ferromagnetic transition at a relatively large
applied magnetic fields. However, for applied aspectes, occurence of
significant CMR at low applied magnetic fields would be required. This review
consists of of two sections: In the first section we have extensively reviewed
the salient features e.g. structure, phase diagram, double exchange mechansim,
Jahn Teller effect, different types of ordering and phase separation of CMR
mangnaites. The second is devoted to an overview of experimental results on CMR
and related magnetotransport characteristics at low magnetic fields for doped
manganites such as polycrystalline La_0.67Ca_0.33MnO_3 films, Ag admixed
La_0.67Ca_0.33MnO_3 films, polycrystalline (La_0.7Ca_0.2Ba_0.1MnO_3)and
epitaxial (La_0.67Ca_0.33MnO_3) films on different substrates, nanophasic
La_0.7Ca_0.3MnO_3, mangnaite-polymer composites (La_0.7Ba_0.2Sr_0.1MnO_3-PMMA
and La_0.67Ca_0.33MnO_3-PMMA)and double layered polycrystalline
(La_1.4Ca_1.6-xBa_xMn_2O_7) and films (La_1.4Ca_1.6Mn_2O_7). Some other
potential magnetoresistive materials e.g. pyrochlores, chalcogenides,
ruthenates, diluted magnetic semiconductors, magnetic tunnel junctions,
nanocontacts etc have aslo been briefly dealt with. The review concludes with
the summary of results for low field magnetotransport behaviour and prospectes
for applications.

###Magnetic and magnetotransport behavior of RFe5Al7 (R= Gd and Dy): Observation of re-entrant inverse-magnetocaloric phenomenon and asymmetric magnetoresistance behavior|Venkatesh Chandragiri,Kartik K Iyer,E. V. Sampathkumaran###

Magnetic and magnetotransport behavior of RFe5Al7 (R= Gd and Dy): Observation of re-entrant inverse-magnetocaloric phenomenon and asymmetric magnetoresistance behavior. We have compared and contrasted magnetic, magnetocaloric and magnetoresistive
properties of Gd and Dy members of the rare-earth (R) series RFe5Al7,
crystallizing in ThMn12 structure, known to order antiferromagnetically. Among
other observations, we would like to emphasize on the following novel findings:
(i) There are multiple sign-crossovers in the temperature (T) dependence of
isothermal entropy change (DeltaS) in the case of Dy compound; in addition to
nil DeltaS at the magnetic compensation point known for two-magnetic-sublattice
systems, there is an additional sign-crossover at low temperatures, as though
there is a re-entrant inverse magnetocaloric phenomenon. Corresponding sign
reversals could also be observed in the magnetoresistance data. (ii) The plots
of magnetoresistance versus magnetic field are found to be highly asymmetric
with the reversal of the direction of magnetic-field (H) well below TN for both
compounds, similar to that known for an antiferromagnetic tunnel junctions. We
attribute these to subtle changes in spin orientations of R and Fe moments
induced by T and H.

###Co-doped (La,Sr)TiO3-d: a high-Curie temperature diluted magnetic system with large spin-polarization|G. Herranz,R. Ranchal,M. Bibes,H. Jaffres,E. Jacquet,J. L. Maurice,K. Bouzehouane,F. Wyczisk,E. Tafra,M. Basletic,A. Hamzic,C. Colliex,J. -P. Contour,A. Barthelemy,A. Fert###

Co-doped (La,Sr)TiO3-d: a high-Curie temperature diluted magnetic system with large spin-polarization. We report on tunneling magnetoresistance (TMR) experiments that demonstrate
the existence of a significant spin polarization in Co-doped (La,Sr)TiO3-d
(Co-LSTO), a ferromagnetic diluted magnetic oxide system (DMOS) with high Curie
temperature. These TMR experiments have been performed on magnetic tunnel
junctions associating Co-LSTO and Co electrodes. Extensive structural analysis
of Co-LSTO combining high-resolution transmission electron microscopy and Auger
electron spectroscopy excluded the presence of Co clusters in the Co-LSTO layer
and thus, the measured ferromagnetism and high spin polarization are intrinsic
properties of this DMOS. Our results argue for the DMOS approach with complex
oxide materials in spintronics.

###One million percent tunnel magnetoresistance in a magnetic van der Waals heterostructure|Hyun Ho Kim,Bowen Yang,Tarun Patel,Francois Sfigakis,Chenghe Li,Shangjie Tian,Hechang Lei,Adam W. Tsen###

One million percent tunnel magnetoresistance in a magnetic van der Waals heterostructure. We report the observation of a very large negative magnetoresistance effect
in a van der Waals tunnel junction incorporating a thin magnetic semiconductor,
CrI3, as the active layer. At constant voltage bias, current increases by
nearly one million percent upon application of a 2 Tesla field. The effect
arises from a change between antiparallel to parallel alignment of spins across
the different CrI3 layers. Our results elucidate the nature of the magnetic
state in ultrathin CrI3 and present new opportunities for spintronics based on
two-dimensional materials.

###Brillouin zone spin filtering mechanism of enhanced TMR and correlation effects in Co(0001)/h-BN/Co(0001) magnetic tunnel junction|Sergey V. Faleev,Stuart S. P. Parkin,Oleg N. Mryasov###

Brillouin zone spin filtering mechanism of enhanced TMR and correlation effects in Co(0001)/h-BN/Co(0001) magnetic tunnel junction. The 'Brillouin zone spin filtering' mechanism of enhanced tunneling
magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJ) and
studied on an example of the MTJ with hcp Co electrodes and hexagonal BN (h-BN)
spacer. Our calculations based on local density approximation of density
functional theory (LDA-DFT) for Co(0001)/h-BN/Co(0001) MTJ predict high TMR in
this device due to Brillouin zone filtering mechanism. Owning to the specific
complex band structure of the h-BN the spin-dependent tunneling conductance of
the system is ultra-sensitive to small variations of the Fermi energy position
inside the BN band gap. Doping of the BN and, consequentially, changing the
Fermi energy position could lead to variation of the TMR by several orders of
magnitude. We show also that taking into account correlation effects on beyond
DFT level is required to accurately describe position of the Fermi level and
thus transport propertied of the system. Our study suggests that new MTJ based
on hcp Co-Pt or Co-Pd disordered alloy electrodes and p-doped hexagonal BN
spacer is a promising candidate for the spin-transfer torque magnetoresistive
random-access memory (STT-MRAM).

###Long-ranged magnetic proximity effects in noble metal-doped cobalt probed with spin- dependent tunnelling|Mihai S. Gabureac,Donald A. Mac Laren,Hervé Courtois,Christopher M. Marrows###

Long-ranged magnetic proximity effects in noble metal-doped cobalt probed with spin- dependent tunnelling. We inserted non-magnetic layers of Au and Cu into sputtered AlOx-based
magnetic tunnel junctions and Meservey-Tedrow junctions in order to study their
effect on tunnelling magnetoresistance (TMR) and spin polarization (TSP). When
either Au or Cu are inserted into a Co/AlOx interface, we find that TMR and TSP
remain finite and measurable for thicknesses up to several nanometres.
High-resolution transmission electron microscopy shows that the Cu and Au
interface layers are fully continuous when their thickness exceeds ~3 nm,
implying that spin-polarized carriers penetrate the interface noble metal to
dis- tances exceeding this value. A power law model based on exchange
scattering is found to fit the data better than a phenomenological exponential
decay. The discrepancy between these length scales and the much shorter ones
reported from x-ray magnetic circular dichroism studies of magnetic
proximitization is ascribed to the fact that our tunnelling transport
measurements selectively probe s-like electrons close to the Fermi level. When
a 0.1 nm thick Cu or Au layer is inserted within the Co, we find that the
suppression of TMR and TSP is restored on a length scale of <=1 nm, indicating
that this is a sufficient quantity of Co to form a fully spin-polarized band
structure at the interface with the tunnel barrier.

###Voltage Control of a van der Waals Spin-Filter Magnetic Tunnel Junction|Tiancheng Song,Matisse Wei-Yuan Tu,Caitlin Carnahan,Xinghan Cai,Takashi Taniguchi,Kenji Watanabe,Michael A. McGuire,David H. Cobden,Di Xiao,Wang Yao,Xiaodong Xu###

Voltage Control of a van der Waals Spin-Filter Magnetic Tunnel Junction. Atomically thin chromium triiodide (CrI3) has recently been identified as a
layered antiferromagnetic insulator, in which adjacent ferromagnetic monolayers
are antiferromagnetically coupled. This unusual magnetic structure naturally
comprises a series of anti-aligned spin filters which can be utilized to make
spin-filter magnetic tunnel junctions with very large tunneling
magnetoresistance (TMR). Here we report voltage control of TMR formed by
four-layer CrI3 sandwiched by monolayer graphene contacts in a dual-gated
structure. By varying the gate voltages at fixed magnetic field, the device can
be switched reversibly between bistable magnetic states with the same net
magnetization but drastically different resistance (by a factor of ten or
more). In addition, without switching the state, the TMR can be continuously
modulated between 17,000% and 57,000%, due to the combination of spin-dependent
tunnel barrier with changing carrier distributions in the graphene contacts.
Our work demonstrates new kinds of magnetically moderated transistor action and
opens up possibilities for voltage-controlled van der Waals spintronic devices.

###Temperature and voltage dependence of magnetic barrier junctions with a nonmagnetic spacer|Ali A. Shokri,Alireza Saffarzadeh###

Temperature and voltage dependence of magnetic barrier junctions with a nonmagnetic spacer. The temperature and voltage dependence of spin transport is theoretically
investigated in a new type of magnetic tunnel junction, which consists of two
ferromagnetic outer electrodes separated by a ferromagnetic barrier and a
nonmagnetic (NM) metallic spacer. The effect of spin fluctuation in magnetic
barrier, which plays an important role at finite temperature, is included by
taking the mean-field approximation. It is found that, the tunnel
magnetoresistance (TMR) and the electron-spin polarization depend strongly on
the temperature and the applied voltage. The TMR and spin polarization at
different temperatures show an oscillatory behavior as a function of the NM
spacer thickness. Also, the amplitude of these oscillations is regularly
reduced when the temperature increases. The maximum TMR value, varies
approximately from 270% in reverse bias (at $T$=0 K) to 25% in forward bias (at
$T\geq T_C$).

###Large Magnetoresistance in a Manganite Spin-Tunnel-Junction Using LaMnO3 as Insulating Barrier|S. Yunoki,E. Dagotto,S. Costamagna,J. A. Riera###

Large Magnetoresistance in a Manganite Spin-Tunnel-Junction Using LaMnO3 as Insulating Barrier. A spin-tunnel-junction based on manganites, with La$_{1-x}$Sr$_x$MnO$_3$
(LSMO) as ferromagnetic metallic electrodes and the undoped parent compound
LaMnO$_3$ (LMO) as insulating barrier, is here theoretically discussed using
double exchange model Hamiltonians and numerical techniques. For an even number
of LMO layers, the ground state is shown to have anti-parallel LSMO magnetic
moments. This highly resistive, but fragile, state is easily destabilized by
small magnetic fields, which orient the LSMO moments in the direction of the
field. The magnetoresistance associated with this transition is very large,
according to Monte Carlo and Density Matrix Renormalization Group studies. The
influence of temperature, the case of an odd number of LMO layers, and the
differences between LMO and SrTiO$_3$ as barriers are also addressed. General
trends are discussed.

###Detection of HIV-1 antigen based on magnetic tunnel junction sensor and magnetic nanoparticles|L. Li,K. Y. Mak,Y. Zhou,W. W. Wang,P. W. T. Pong###

Detection of HIV-1 antigen based on magnetic tunnel junction sensor and magnetic nanoparticles. In recent years, it is evidenced that the individuals newly infected HIV are
transmitting the virus prior to knowing their HIV status. Identifying
individuals that are early in infection with HIV antibody negative (window
period) remains problematic. In the newly infected individuals, HIV antigen p24
is usually present in their serum or plasma 7-10 days before the HIV antibody.
After antibody production initiates, the p24 antigen is bound into immune
complexes. That means the detectable p24 antigens in serum/plasma are
short-lived, and their amount is in the pg/ml range. Thus, a rapid quantitative
bio-detection system with high-sensitivity is required to achieve early disease
diagnosis. Magnetoresistive (MR) biosensor with ultra-high sensitivity
possesses great potential in this area. In this study, a p24 detection assay
using MgO-based magnetic tunnel junction (MTJ) sensor and 20-nm magnetic
nanoparticles is reported.

###Perspectives in spintronics: magnetic resonant tunneling, spin-orbit coupling, and GaMnAs|C. Ertler,A. Matos-Abiague,M. Gmitra,M. Turek,J. Fabian###

Perspectives in spintronics: magnetic resonant tunneling, spin-orbit coupling, and GaMnAs. Spintronics has attracted wide attention by promising novel functionalities
derived from both the electron charge and spin. While branching into new areas
and creating new themes over the past years, the principal goals remain the
spin and magnetic control of the electrical properties, essentially the I-V
characteristics, and vice versa. There are great challenges ahead to meet these
goals. One challenge is to find niche applications for ferromagnetic
semiconductors, such as GaMnAs. Another is to develop further the science of
hybrid ferromagnetic metal/semiconductor heterostructures, as alternatives to
all-semiconductor room temperature spintronics. Here we present our
representative recent efiorts to address such challenges. We show how to make a
digital magnetoresistor by combining two magnetic resonant diodes, or how
introducing ferromagnetic semiconductors as active regions in resonant
tunneling diodes leads to novel efiects of digital magnetoresistance and of
magnetoelectric current oscillations. We also discuss the phenomenon of
tunneling anisotropic magnetoresistance in Fe/GaAs junctions by introducing the
concept of the spin-orbit coupling field, as an analog of such fields in
all-semiconductor junctions. Finally, we look at fundamental electronic and
optical properties of GaMnAs by employing reasonable tight-binding models to
study disorder efiects.

###The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures|Ali A. Shokri,Alireza Saffarzadeh###

The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures. The spin-polarized transport is investigated in a new type of magnetic tunnel
junction which consists of two ferromagnetic electrodes separated by a magnetic
barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method
and the nearly-free-electron-approximation the dependence of the tunnel
magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer
thickness and the applied bias voltage are studied theoretically. The TMR and
spin polarization show an oscillatory behavior as a function of the spacer
thickness and the bias voltage. The oscillations originate from the quantum
well states in the spacer, while the existence of the magnetic barrier gives
rise to a strong spin polarization and high values of the TMR. Our results may
be useful for the development of spin electronic devices based on coherent
transport.

###Spin diffusion and magnetoresistance in ferromagnet/topological-insulator junctions|Takehito Yokoyama,Yaroslav Tserkovnyak###

Spin diffusion and magnetoresistance in ferromagnet/topological-insulator junctions. We study spin and charge diffusion in
metallic-ferromagnet/topological-insulator junctions. The coupled diffusion
equations are derived perturbatively with respect to the strength of the
interlayer tunneling. We calculate spin accumulation in the ferromagnet and
junction magnetoresistance associated with a current bias along the interface.

###Anisotropic magnetotransport in Dirac-Weyl magnetic junctions|Yuya Ominato,Koji Kobayashi,Kentaro Nomura###

Anisotropic magnetotransport in Dirac-Weyl magnetic junctions. We theoretically study the anisotropic magnetotransport in Dirac-Weyl
magnetic junctions where a doped ferromagnetic Weyl semimetal is sandwiched
between doped Dirac semimetals. We calculate the conductance using the Landauer
formula and find that the system exhibits extraordinarily large anisotropic
magnetoresistance (AMR). The AMR depends on the ratio of the Fermi energy and
the strength of the exchange interaction. The origin of the AMR is the shift of
the Fermi surface in the Weyl semimetal and the mechanism is completely
different from the conventional AMR originating from the spin dependent
scattering and the spin-orbit interaction.

###Physical Vapor Transport Growth of Antiferromagnetic CrCl$_3$ Flakes Down to Monolayer Thickness|Jia Wang,Zahra Ahmadi,David Lujan,Jeongheon Choe,Takashi Taniguchi,Kenji Watanabe,Xiaoqin Li,Jeffrey E. Shield,Xia Hong###

Physical Vapor Transport Growth of Antiferromagnetic CrCl$_3$ Flakes Down to Monolayer Thickness. The van der Waals magnets CrX$_3$ (X = I, Br, and Cl) exhibit highly tunable
magnetic properties and are promising candidates for developing novel
two-dimensional (2D) magnetic devices such as magnetic tunnel junctions and
spin tunneling transistors. Previous studies of CrCl$_3$ have mainly focused on
mechanically exfoliated samples. Controlled synthesis of high quality
atomically thin flakes is critical for their technological implementation but
has not been achieved to date. Here, we report the growth of large CrCl$_3$
flakes with well-defined facets down to monolayer thickness (~0.6 nm) via the
physical vapor transport technique. Both isolated flakes with well-defined
facets and long stripe samples with the trilayer portion exceeding 60 $\mu$m
have been obtained. High-resolution transmission electron microscopy studies
show that the CrCl$_3$ flakes are single crystalline in the monoclinic
structure, consistent with the Raman results. The room temperature stability of
the CrCl$_3$ flakes decreases with decreasing thickness. The tunneling
magnetoresistance of graphite/CrCl$_3$/graphite tunnel junctions confirms that
few-layer CrCl$_3$ possesses in-plane magnetic anisotropy and N\'eel
temperature of 17 K. Our study paves the path for developing CrCl$_3$-based
scalable 2D spintronic applications.

###Magnetoresistive Sensor Detectivity: A Comparative Analysis|J. E. Davies,J. D. Watts,J. Novotny,D. Huang,P. G. Eames###

Magnetoresistive Sensor Detectivity: A Comparative Analysis. We report on the noise performance characteristics of magnetic sensors using
both magnetic tunnel junction (MTJ) and giant magnetoresistance (GMR) elements.
Each sensor studied has a notably different noise and detectivity. Of the
sensors we measured, those based on GMR multilayers have the lowest noise and
detectivity. However, the GMR sensor also has a significantly smaller linear
range. To make a direct comparison between sensors we scale the linear
operating ranges of each sensor to be the same. This is the phenomenological
equivalent of modifying the flux concentration. Upon scaling the low frequency
detectivity of the TMR sensors becomes essentially equal to that of the GMR
sensor. Using the scaling approach we are able to place the detectivity in the
context of other key parameters, namely size and power consumption. Lastly, we
use this technique to examine the upper limit for magnetoresistive sensor
performance based on a notional MTJ sensor using present record setting TMR
values.

###Thermal Stability and Electrical Control of Magnetization of Heusler/Oxide Interface and Non-collinear Spin Transport of Its Junction|Zhaoqiang Bai,Lei Shen,Yongqing Cai,Qingyun Wu,Minggang Zeng,Guchang Han,Yuan Ping Feng###

Thermal Stability and Electrical Control of Magnetization of Heusler/Oxide Interface and Non-collinear Spin Transport of Its Junction. Towards next-generation spintronics devices, such as computer memories and
logic chips, it is necessary to satisfy high thermal stability, low-power
consumption and high spin-polarization simultaneously. Here, from
first-principles, we investigate thermal stability (both structure and
magnetization) and the electric field control of magnetic anisotropy on Co2FeAl
(CFA)/MgO. A phase diagram of structural thermal stability of the CFA/MgO
interface is illustrated. An interfacial perpendicular-anisotropy, coming from
the Fe-O orbital hybridization, provides high magnetic thermal stability and a
low stray field. We find an electric-field-induced giant modification of such
perpendicular-anisotropy via a great magnetoelectric effect (the anisotropy
energy coefficient beta~10-7 erg/V cm). Our spin electronic-structure and
non-collinear transport calculations indicate high spin-polarized interfacial
states and good magnetoresistance properties of CFA/MgO/CFA perpendicular
magnetic tunnel junctions.

###Spin dependent transport of ``nonmagnetic metal/zigzag nanotube encapsulating magnetic atoms/nonmagnetic metal'' junctions|Satoshi Kokado,Kikuo Harigaya###

Spin dependent transport of ``nonmagnetic metal/zigzag nanotube encapsulating magnetic atoms/nonmagnetic metal'' junctions. Towards a novel magnetoresistance (MR) device with a carbon nanotube, we
propose ``nonmagnetic metal/zigzag nanotube encapsulating magnetic
atoms/nonmagnetic metal'' junctions. We theoretically investigate how
spin-polarized edges of the nanotube and the encapsulated magnetic atoms
influence on transport. When the on-site Coulomb energy divided by the
magnitude of transfer integral, $U/|t|$, is larger than 0.8, large MR effect
due to the direction of spins of magnetic atoms, which has the magnitude of the
MR ratio of about 100%, appears reflecting such spin-polarized edges.

###Prospect for room temperature tunneling anisotropic magnetoresistance effect: density of states anisotropies in CoPt systems|A. B. Shick,F. Maca,J. Masek,T. Jungwirth###

Prospect for room temperature tunneling anisotropic magnetoresistance effect: density of states anisotropies in CoPt systems. Tunneling anisotropic magnetoresistance (TAMR) effect, discovered recently in
(Ga,Mn)As ferromagnetic semiconductors, arises from spin-orbit coupling and
reflects the dependence of the tunneling density of states in a ferromagnetic
layer on orientation of the magnetic moment. Based on ab initio relativistic
calculations of the anisotropy in the density of states we predict sizable TAMR
effects in room-temperature metallic ferromagnets. This opens prospect for new
spintronic devices with a simpler geometry as these do not require
antiferromagnetically coupled contacts on either side of the tunnel junction.
We focus on several model systems ranging from simple hcp-Co to more complex
ferromagnetic structures with enhanced spin-orbit coupling, namely bulk and
thin film L1$_0$-CoPt ordered alloys and a monatomic-Co chain at a Pt surface
step edge. Reliability of the predicted density of states anisotropies is
confirmed by comparing quantitatively our ab initio results for the
magnetocrystalline anisotropies in these systems with experimental data.

###Spin Transfer Torque and Tunneling Magnetoresistance Dependences on the Finite Bias Voltages and Insulator Barrier Energy|Chun-Yeol You,Jae-Ho Han,Hyun-Woo Lee###

Spin Transfer Torque and Tunneling Magnetoresistance Dependences on the Finite Bias Voltages and Insulator Barrier Energy. We investigate the dependence of perpendicular and parallel spin transfer
torque (STT) and tunneling magnetoresistance (TMR) on the insulator barrier
energy in the magnetic tunnel junction (MTJ). We employed single orbit tight
binding model combined with the Keldysh non-equilibrium Green's function method
in order to calculate the perpendicular and parallel STT, and TMR in MTJ with
the finite bias voltages. The dependences of STT and TMR on the insulator
barrier energy are calculated for the semi-infinite half metallic ferromagnetic
electrodes. We find that perfect linear relation between the parallel STT and
the tunneling current for the wide range of the insulator barrier energy.
Furthermore, the TMR also depends on the insulator barrier energy, which
contradicts to the Julliere's simple model.

###Interface effects in spin-dependent tunneling|E. Y. Tsymbal,K. D. Belashchenko,J. P. Velev,S. S. Jaswal,M. van Schilfgaarde,I. I. Oleynik,D. A. Stewart###

Interface effects in spin-dependent tunneling. In the past few years the phenomenon of spin dependent tunneling (SDT) in
magnetic tunnel junctions (MTJs) has aroused enormous interest and has
developed into a vigorous field of research. The large tunneling
magnetoresistance (TMR) observed in MTJs garnered much attention due to
possible application in random access memories and magnetic field sensors. This
led to a number of fundamental questions regarding the phenomenon of SDT. One
such question is the role of interfaces in MTJs and their effect on the spin
polarization of the tunneling current and TMR. In this paper we consider
different models which suggest that the spin polarization is primarily
determined by the electronic and atomic structure of the ferromagnet/insulator
interfaces rather than by their bulk properties. First, we consider a simple
tight-binding model which demonstrates that the existence of interface states
and their contribution to the tunneling current depend on the degree of
hybridization between the orbitals on metal and insulator atoms. The decisive
role of the interfaces is further supported by studies of spin-dependent
tunneling within realistic first-principles models of Co/vacuum/Al,
Co/Al2O3/Co, Fe/MgO/Fe, and Co/SrTiO3/Co MTJs. We find that variations in the
atomic potentials and bonding strength near the interfaces have a profound
effect resulting in the formation of interface resonant states, which
dramatically affect the spin polarization and TMR. The strong sensitivity of
the tunneling spin polarization and TMR to the interface atomic and electronic
structure dramatically expands the possibilities for engineering optimal MTJ
properties for device applications.

###Angular dependence of the tunneling anisotropic magnetoresistance|A. Matos-Abiague,M. Gmitra,J. Fabian###

Angular dependence of the tunneling anisotropic magnetoresistance. Based on general symmetry considerations we investigate how the dependence of
the tunneling anisotropic magnetoresistance (TAMR) on the magnetization
direction is determined by the specific form of the spin-orbit coupling field.
By extending a phenomenological model, previously proposed for explaining the
main trends of the TAMR in (001) ferromagnet/semiconductor/normal-metal
magnetic tunnel junctions (MTJs) [J. Moser {\it et al.}, Phys. Rev. Lett. 99,
056601 (2007)], we provide a unified qualitative description of the TAMR in
MTJs with different growth directions. In particular, we predict the forms of
the angular dependence of the TAMR in (001),(110), and (111) MTJs with
structure inversion asymmetry and/or bulk inversion asymmetry. The effects of
in-plane uniaxial strain on the TAMR are also investigated.

###A Piezoelectric, Strain-Controlled Antiferromagnetic Memory Insensitive to Magnetic Fields|Han Yan,Zexin Feng,Shunli Shang,Xiaoning Wang,Zexiang Hu,Jinhua Wang,Zengwei Zhu,Hui Wang,Zuhuang Chen,Hui Hua,Wenkuo Lu,Jingmin Wang,Peixin Qin,Huixin Guo,Xiaorong Zhou,Zhaoguogang Leng,Zikui Liu,Chengbao Jiang,Michael Coey,Zhiqi Liu###

A Piezoelectric, Strain-Controlled Antiferromagnetic Memory Insensitive to Magnetic Fields. Spintronic devices based on antiferromagnetic (AFM) materials hold the
promise of fast switching speeds and robustness against magnetic fields.
Different device concepts have been predicted and experimentally demonstrated,
such as low-temperature AFM tunnel junctions that operate as spin-valves, or
room-temperature AFM memory, for which either thermal heating in combination
with magnetic fields, or N\'eel spin-orbit torque is used for the information
writing process. On the other hand, piezoelectric materials were employed to
control magnetism by electric fields in multiferroic heterostructures, which
suppresses Joule heating caused by switching currents and may enable low
energy-consuming electronic devices. Here, we combine the two material classes
to explore changes of the resistance of the high-N\'eel-temperature
antiferromagnet MnPt induced by piezoelectric strain. We find two non-volatile
resistance states at room temperature and zero electric field, which are stable
in magnetic fields up to 60 T. Furthermore, the strain-induced resistance
switching process is insensitive to magnetic fields. Integration in a tunnel
junction can further amplify the electroresistance. The tunneling anisotropic
magnetoresistance reaches ~11.2% at room temperature. Overall, we demonstrate a
piezoelectric, strain-controlled AFM memory which is fully operational in
strong magnetic fields and has potential for low-energy and high-density memory
applications.

###Bias dependence of tunneling magnetoresistance in magnetic tunnel junctions with asymmetric barriers|Alan Kalitsov,Pierre-Jean Zermatten,Frédéric Bonell,Gilles Gaudin,Stéphane Andrieu,Coriolan Tiusan,Mairbek Chshiev,Julian P. Velev###

Bias dependence of tunneling magnetoresistance in magnetic tunnel junctions with asymmetric barriers. The transport properties of magnetic tunnel junctions (MTJs) are very
sensitive to interface modifications. In this work we investigate both
experimentally and theoretically the effect of asymmetric barrier modifications
on the bias dependence of tunneling magnetoresistance (TMR) in single crystal
Fe/MgO-based MTJs with (i) one crystalline and one rough interface and (ii)
with a monolayer of O deposited at the crystalline interface. In both cases we
observe an asymmetric bias dependence of TMR and a reversal of its sign at
large bias. We propose a general model to explain the bias dependence in these
and similar systems reported earlier. The model predicts the existence of two
distinct TMR regimes: (i) tunneling regime when the interface is modified with
layers of a different insulator and (ii) resonant regime when thin metallic
layers are inserted at the interface. We demonstrate that in the tunneling
regime negative TMR is due to the high voltage which overcomes the exchange
splitting in the electrodes, while the asymmetric bias dependence of TMR is due
to the interface transmission probabilities. In the resonant regime inversion
of TMR could happen at zero voltage depending on the alignment of the resonance
levels with the Fermi surfaces of the electrodes. Moreover, the model predicts
a regime in which TMR has different sign at positive and negative bias
suggesting possibilities of combining memory with logic functions.

###Temperature effects of the magnetic tunnel junctions with periodic grating barrier|Henan Fang,Mingwen Xiao,Wenbin Rui,Jun Du,Zhikuo Tao###

Temperature effects of the magnetic tunnel junctions with periodic grating barrier. We have developed a tunneling theory to describe the temperature dependence
of tunneling magnetoresistance (TMR) of the magnetic tunnel junctions (MTJs)
with periodic grating barrier. Through the Patterson function approach, the
theory can handle easily the influence of the lattice distortion of the barrier
on the tunneling process of the electrons. The lattice distortion of the
barrier is sensible to the temperature and can be quite easily weakened by the
thermal relaxation of the strain, and thus the tunneling process of the
electrons gets changed highly with the variation of the temperature of the
system. That is just the physical mechanism for the temperature dependence of
the TMR. From it, we find that the decrease of TMR with rising temperature is
mostly carried by a change in the antiparallel resistance ($R_{AP}$), and the
parallel resistance ($R_{P}$) changes so little that it seems roughly constant,
if compared to the $R_{AP}$, and that, for the annealed MTJ, the $R_{AP}$ is
significantly more sensitive to the strain than the $R_{P}$, and for
non-annealed MTJ, both the $R_{P}$ and $R_{AP}$ are not sensitive to the
strain. They are both in agreement with the experiments of the MgO-based MTJs.
Other relevant properties are also discussed.

###Structural relaxation effects on interface and transport properties of Fe/MgO(001) tunnel junctions|Xiaobing Feng,O. Bengone,M. Alouani,S. Lebégue,I. Rungger,S. Sanvito###

Structural relaxation effects on interface and transport properties of Fe/MgO(001) tunnel junctions. The interface structure of Fe/MgO(100) magnetic tunnel junctions predicted by
density functional theory (DFT) depends significantly on the choice of exchange
and correlation functional. Bader analysis reveals that structures obtained by
relaxing the cell with the local spin-density approximation (LSDA) display a
different charge transfer than those relaxed with the generalized gradient
approximation (GGA). As a consequence, the electronic transport is found to be
extremely sensitive to the interface structure. In particular, the conductance
for the LSDA-relaxed geometry is about one order of magnitude smaller than that
of the GGA-relaxed one. The high sensitivity of the electronic current to the
details of the interface might explain the discrepancy between the experimental
and calculated values of magnetoresistance.

###Influence of the magnetic material on tunneling magnetoresistance and spin-transfer torque in tunnel junctions: Ab initio studies|Christian Franz,Michael Czerner,Christian Heiliger###

Influence of the magnetic material on tunneling magnetoresistance and spin-transfer torque in tunnel junctions: Ab initio studies. The dependence of tunneling magnetoresistance and spin-transfer torque in
FeCo/MgO/FeCo tunnel junctions on the Co concentration and the bias voltage are
investigated ab initio. We find that the tunneling magnetoresistance decreases
with the Co concentration in contradiction with previous calculations but in
agreement with recent experiments. This dependence is explained from bulk
properties of the alloys. By using a realistic description of the disorder in
the alloys we can show that even small amounts of disorder lead to a drastic
drop in the tunneling magnetoresistance. This provides a quantitative
explanation of the difference between calculated and measured values.
  The spin-transfer torque shows a linear voltage dependence for the in-plane
component and a quadratic for the out-of-plane component for all concentrations
at small bias voltages. In particular, the linear slope of the in-plane torque
is independent of the concentration. For high bias voltages the in-plane torque
shows a strong nonlinear deviation from the linear slope for high Co
concentrations. This is explained from the same effects which govern the
tunneling magnetoresistance.

###Observation of minority spin character of the new electron doped manganite La_0.7Ce_0.3MnO_3 from tunneling magnetoresistance|C. Mitra,P. Raychaudhuri,K. Doerr,K. -H. Mueller,L. Schultz,P. M. Oppeneer,S. Wirth###

Observation of minority spin character of the new electron doped manganite La_0.7Ce_0.3MnO_3 from tunneling magnetoresistance. We report the magnetotransport characteristics of a trilayer ferromagnetic
tunnel junction build of an electron doped manganite (La_0.7Ce_0.3MnO_3) and a
hole doped manganite (La_0.7Ca_0.3MnO_3). At low temperatures the junction
exhibits a large positive tunneling magnetoresistance (TMR), irrespective of
the bias voltage. At intermediate temperatures below T_C the sign of the TMR is
dependent on the bias voltage across the junction. The magnetoresistive
characteristics of the junction strongly suggest that La_0.7Ce_0.3MnO_3 is a
minority spin carrier ferromagnet with a high degree of spin polarization, i.e.
a transport half metal.

###Spin-valve Effect in NiFe/MoS2/NiFe Junctions|Weiyi Wang,Awadhesh Narayan,Lei Tang,Kapildeb Dolui,Yanwen Liu,Xiang Yuan,Yibo Jin,Yizheng Wu,Ivan Rungger,Stefano Sanvito,Faxian Xiu###

Spin-valve Effect in NiFe/MoS2/NiFe Junctions. Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have
been recently proposed as appealing candidate materials for spintronic
applications owing to their distinctive atomic crystal structure and exotic
physical properties arising from the large bonding anisotropy. Here we
introduce the first MoS2-based spin-valves that employ monolayer MoS2 as the
nonmagnetic spacer. In contrast with what expected from the semiconducting
band-structure of MoS2, the vertically sandwiched-MoS2 layers exhibit metallic
behavior. This originates from their strong hybridization with the Ni and Fe
atoms of the Permalloy (Py) electrode. The spin-valve effect is observed up to
240 K, with the highest magnetoresistance (MR) up to 0.73% at low temperatures.
The experimental work is accompanied by the first principle electron transport
calculations, which reveal an MR of ~ 9% for an ideal Py/MoS2/Py junction. Our
results clearly identify TMDs as a promising spacer compound in magnetic tunnel
junctions and may open a new avenue for the TMDs-based spintronic applications.

###Ion beam modification of magnetic tunnel junctions|B. M. S. Teixeira,A. A. Timopheev,N. Caçoilo,L. Cuchet,J. Mondaud,J. R. Childress,S. Magalhães,E. Alves,N. A. Sobolev###

Ion beam modification of magnetic tunnel junctions. The impact of 400 keV $Ar^+$ ion irradiation on the magnetic and electrical
properties of in-plane magnetized magnetic tunnel junction (MTJ) stacks was
investigated by ferromagnetic resonance, vibrating sample magnetometry and
current-in-plane tunneling techniques. The irradiation-induced changes of the
magnetic anisotropy, coupling energies and tunnel magnetoresistance (TMR)
exhibited a correlated dependence on the ion fluence, which allowed us to
distinguish between two irradiation regimes. In the low-fluence regime, ${\Phi}
< 10^{14} cm^{-2}$, the parameters required for having a functioning MTJ were
preserved: the anisotropy of the FeCoB free layer (FL) was weakly modulated
following a small decrease in the saturation magnetization $M_S$; the TMR
decreased continuously; the interlayer exchange coupling (IEC) and the exchange
bias (EB) decreased slightly. In the high-fluence regime, ${\Phi} > 10^{14}
cm^{-2}$, the MTJ was rendered inoperative: the modulation of the FL anisotropy
was strong, caused by a strong decrease in $M_S$, ascribed to a high degree of
interface intermixing between the FL and the Ta capping; the EB and IEC were
also lost, likely due to intermixing of the layers composing the synthetic
antiferromagnet; and the TMR vanished due to the irradiation-induced
deterioration of the MgO barrier and MgO/FeCoB interfaces. We demonstrate that
the layers surrounding the FL play a decisive role in determining the trend of
the magnetic anisotropy evolution resulting from the irradiation, and that an
ion-fluence window exists where such a modulation of magnetic anisotropy can
occur, while not losing the TMR or the magnetic configuration of the MTJ.

###Cryogenic temperature deposition of high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions on 300 mm wafers|Tomohiro Ichinose,Tatsuya Yamamoto,Takayuki Nozaki,Kay Yakushiji,Shingo Tamaru,Makoto Konoto,Shinji Yuasa###

Cryogenic temperature deposition of high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions on 300 mm wafers. We developed a cryogenic temperature deposition process for high-performance
CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on 300 mm thermally oxidized
silicon wafers. The effect of the deposition temperature of the CoFeB layers on
the nanostructure, magnetic and magneto-transport properties of the MTJs were
investigated in detail. When CoFeB was deposited at 100 K, the MTJs exhibited a
perpendicular magnetic anisotropy (PMA) of 214 uJ/m2 and a voltage-controlled
magnetic anisotropy (VCMA) coefficient of -45 fJ/Vm, corresponding to 1.4- and
1.7-fold enhancements in PMA and VCMA, respectively, compared to the case of
room-temperature deposition of CoFeB. The improvement in the MTJ properties was
not simply due to the morphology of the MTJ films. The interface-sensitive
magneto-transport properties indicated that interfacial qualities such as
intermixing and oxidation states at the MgO/CoFeB interfaces were improved by
the cryogenic temperature deposition. Cryogenic-temperature sputtering
deposition is expected to be a standard manufacturing process for
next-generation magnetoresistive random-access memory.

###Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers|N. Wiese,T. Dimopoulos,M. Ruhrig,J. Wecker,H. Bruckl,G. Reiss###

Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers. This work reports on the magnetic interlayer coupling between two amorphous
CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic
coupling which oscillates as a function of the Ru thickness x, with the second
antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the
switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found
that the coercivity depends on the net magnetic moment, i.e. the thickness
difference of the two CoFeB layers. The antiferromagnetic coupling is almost
independent on the annealing temperatures up to 300 degree C while an annealing
at 350 degree C reduces the coupling and increases the coercivity, indicating
the onset of crystallization. Used as a soft electrode in a magnetic tunnel
junction, a high tunneling magnetoresistance of about 50%, a well defined
plateau and a rectangular switching behavior is achieved.

###Spin Tunneling in Conducting Oxides|Alexander Bratkovsky###

Spin Tunneling in Conducting Oxides. Direct tunneling in ferromagnetic junctions is compared with
impurity-assisted, surface state assisted, and inelastic contributions to a
tunneling magnetoresistance (TMR). Theoretically calculated direct tunneling in
iron group systems leads to about a 30% change in resistance, which is close to
experimentally observed values. It is shown that the larger observed values of
the TMR might be a result of tunneling involving surface polarized states. We
find that tunneling via resonant defect states in the barrier radically
decreases the TMR (down to 4% with Fe-based electrodes), and a resonant tunnel
diode structure would give a TMR of about 8%. With regards to inelastic
tunneling, magnons and phonons exhibit opposite effects: one-magnon emission
generally results in spin mixing and, consequently, reduces the TMR, whereas
phonons are shown to enhance the TMR. The inclusion of both magnons and phonons
reasonably explains an unusual bias dependence of the TMR.
  The model presented here is applied qualitatively to half-metallics with 100%
spin polarization, where one-magnon processes are suppressed and the change in
resistance in the absence of spin-mixing on impurities may be arbitrarily
large. Even in the case of imperfect magnetic configurations, the resistance
change can be a few 1000 percent. Examples of half-metallic systems are
CrO$_2$/TiO$_2$ and CrO$_2$/RuO$_2$, and an account of their peculiar band
structures is presented. The implications and relation of these systems to CMR
materials which are nearly half-metallic, are discussed.

###Atomically Thin CrCl3: An in-Plane Layered Antiferromagnetic Insulator|Xinghan Cai,Tiancheng Song,Nathan P. Wilson,Genevieve Clark,Minhao He,Xiaoou Zhang,Takashi Taniguchi,Kenji Watanabe,Wang Yao,Di Xiao,Michael A. McGuire,David H. Cobden,Xiaodong Xu###

Atomically Thin CrCl3: An in-Plane Layered Antiferromagnetic Insulator. The recent discovery of magnetism in atomically thin layers of van der Waals
(vdW) crystals has created new opportunities for exploring magnetic phenomena
in the two-dimensional (2D) limit. In most 2D magnets studied to date the
c-axis is an easy axis, so that at zero applied field the polarization of each
layer is perpendicular to the plane. Here, we demonstrate that atomically thin
CrCl3 is a layered antiferromagnetic insulator with an easy-plane normal to the
c-axis, that is the polarization is in the plane of each layer and has no
preferred direction within it. Ligand field photoluminescence at 870 nm is
observed down to the monolayer limit, demonstrating its insulating properties.
We investigate the in-plane magnetic order using tunneling magnetoresistance in
graphene/CrCl3/graphene tunnel junctions, establishing that the interlayer
coupling is antiferromagnetic down to the bilayer. From the temperature
dependence of the magnetoresistance we obtain an effective magnetic phase
diagram for the bilayer. Our result shows that CrCl3 should be useful for
studying the physics of 2D phase transitions and for making new kinds of vdW
spintronic devices.

###Fluctuation theorem for spin transport at insulating ferromagnetic junctions|Tetsuya Sato,Masahiro Tatsuno,Mamoru Matsuo,Takeo Kato###

Fluctuation theorem for spin transport at insulating ferromagnetic junctions. General relations for nonequilibrium spin transport at a magnetic junction
between a normal metal and a ferromagnetic insulator are derived from the
quantum fluctuation theorem. They include the extended Onsager relations
between the spin conductance and the spin-current noise that hold for
nonequilibrium states driven by an external current. These relations, that are
valid for a general setup of spin Hall magnetoresistance, provide a
comprehensive viewpoint for understanding of unidirectional spin Hall
magnetoresistance in insulating ferromagnetic junctions.

###Electric field tunable multi-state tunnel magnetoresistances in 2D van der Waals magnetic heterojunctions|X. X. Ren,B. Liu,Xian Zhang,Ping Li,Zhi-Xin Guo###

Electric field tunable multi-state tunnel magnetoresistances in 2D van der Waals magnetic heterojunctions. Magnetic tunnel junction (MTJ) based on van der Waals (vdW) magnetic layers
has been found to present excellent tunneling magnetoresistance (TMR) property,
which has great potential applications in field sensing, non-volatile magnetic
random access memories, and spin logics. Although MTJs composed of multilayer
vdW magnetic homojunction have been extensively investigated, the ones composed
of vdW magnetic heterojunction is still to be explored. Here we use
first-principles approaches to reveal that the magnetic heterojunction MTJs
have much more distinguishable TMR values than the homojunction ones. In the
MTJ composed of bilayer CrI3/bilayer Cr2Ge2Te6 heterojunction, we find there
are eight stable magnetic states, leading to six distinguishable electronic
resistances. As a result, five sizable TMRs larger than 300% can be obtained
(the maximum TMR is up to 620,000%). Six distinguishable memories are obtained
which is two times larger than that of a four-layered homojunction MTJ. The
underlying relationships among magnetic state, spin-polarized band structures,
and transmission spectrums are further revealed to explain the multiple TMR
values. We also find that the magnetic states and thus TMRs can be efficiently
modulated by an external electric field. This study opens an avenue to the
design of high-performance MTJ devices based on vdW heterojunctions.

###Negative spin polarization of Mn2VGa probed by tunnel magnetoresistance|Christoph Klewe,Markus Meinert,Jan Schmalhorst,Günter Reiss###

Negative spin polarization of Mn2VGa probed by tunnel magnetoresistance. The ferrimagnetic Heusler compound Mn2VGa is predicted to have a pseudogap in
the majority spin channel, which should lead to a negative tunnel
magnetoresistance. We synthesized epitaxial Mn2VGa thin films on MgO(001)
substrates by dc and rf magnetron co-sputtering, resulting in nearly
stoichiometric films. XRD analysis revealed a mostly B2-ordered structure for
the films deposited at substrate temperatures of 350{\deg}C, 450{\deg}C, and
550{\deg}C. Magnetic tunnel junctions with MgO barrier and CoFe
counter-electrodes were fabricated. After post-annealing at up to
T_a=425{\deg}C negative TMR was obtained around zero bias, providing evidence
for the inverted spin-polarization. Band structures of both electrodes were
computed within the coherent potential approximation and used to calculate the
TMR(V) characteristics, which are in good agreement with our experimental
findings.

###Immunity of nanoscale magnetic tunnel junctions to ionizing radiation|Eric Arturo Montoya,Jen-Ru Chen,Randy Ngelale,Han Kyu Lee,Hsin-Wei Tseng,Lei Wan,En Yang,Patrick Braganca,Ozdal Boyraz,Nader Bagherzadeh,Mikael Nilsson,Ilya N. Krivorotov###

Immunity of nanoscale magnetic tunnel junctions to ionizing radiation. Spin transfer torque magnetic random access memory (STT-MRAM) is a promising
candidate for next generation memory as it is non-volatile, fast, and has
unlimited endurance. Another important aspect of STT-MRAM is that its core
component, the nanoscale magnetic tunneling junction (MTJ), is thought to be
radiation hard, making it attractive for space and nuclear technology
applications. However, studies of the effects of high doses of ionizing
radiation on STT-MRAM writing process are lacking. Here we report measurements
of the impact of high doses of gamma and neutron radiation on nanoscale MTJs
with perpendicular magnetic anistropy used in STT-MRAM. We characterize the
tunneling magnetoresistance, the magnetic field switching, and the
current-induced switching before and after irradiation. Our results demonstrate
that all these key properties of nanoscale MTJs relevant to STT-MRAM
applications are robust against ionizing radiation. Additionally, we perform
experiments on thermally driven stochastic switching in the gamma ray
environment. These results indicate that nanoscale MTJs are promising building
blocks for radiation-hard non-von Neumann computing.

###Recent progress and challenges in magnetic tunnel junctions with 2D materials for spintronic applications|Lishu Zhang,Jun Zhou,Hui Li,Lei Shen,Yuan Ping Feng###

Recent progress and challenges in magnetic tunnel junctions with 2D materials for spintronic applications. As Moore's law is gradually losing its effectiveness, developing alternative
high-speed and low-energy-consuming information technology with post-silicon
advanced materials is urgently needed. The successful application of tunneling
magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) has given rise to a
tremendous economic impact on magnetic informatics, including MRAM,
radio-frequency sensors, microwave generators and neuromorphic computing
networks. The emergence of two-dimensional (2D) materials brings opportunities
for MTJs based on 2D materials which have many attractive characters and
advantages. Especially, the recently discovered intrinsic 2D ferromagnetic
materials with high spin-polarization hold the promise for next-generation
nanoscale MTJs. With the development of advanced 2D materials, many efforts on
MTJs with 2D materials have been made both theoretically and experimentally.
Various 2D materials, such as semi-metallic graphene, insulating h-BN,
semiconducting MoS2, magnetic semiconducting CrI3, magnetic metallic Fe3GeTe2
and some other recently emerged 2D materials are discussed as the electrodes
and/or central scattering materials of MTJs in this review. We discuss the
fundamental and main issues facing MTJs, and review the current progress made
with 2D MTJs, briefly comment on work with some specific 2D materials, and
highlight how they address the current challenges in MTJs, and finally offer an
outlook and perspective of 2D MTJs.

###Iridium Enabled Field-free Spin-orbit Torque Switching of Perpendicular Magnetic Tunnel Junction Device|Yang Liu,Bing Zhou,Zhengkun Dai,Enbo Zhang,Jian-Gang Zhu###

Iridium Enabled Field-free Spin-orbit Torque Switching of Perpendicular Magnetic Tunnel Junction Device. Writing magnetic bits by spin-orbit torques (SOTs) arising from spin Hall
effect creates new possibilities for ultrafast and low-power magnetoresistive
random access memory (MRAM). For perpendicular MRAM, an extra in-plane field is
required to break the symmetry for the deterministic SOT writing of the
perpendicular storage layer. Although schemes have been demonstrated in
external-field-free SOT switching of a perpendicular layer, practically
integrating them with perpendicular MTJs still appears to be challenging. Here,
we present experimental demonstration of spin-orbit torques (SOTs) switching a
perpendicular magnetic tunnel junction (MTJ) device without applying an
external magnetic field. An Ir layer is used to serve dual-purpose of both
injecting the pure spin current via spin Hall effect and mediating an in-plane
exchange field to the perpendicular free layer of the MTJ. Robust field-free
SOT switching with pulsed write path current is demonstrated for various MTJ
sizes ranging from 50 nm to 500 nm. The effect of MTJ size and pulse width on
the critical switching current is studied. Combined micromagnetic simulations
are carried out to provide in-depth analysis of the switching dynamics as well
as the thermal effect on the switching.

###Spincaloric properties of epitaxial Co$_2$MnSi/MgO/Co$_2$MnSi magnetic tunnel junctions|Benjamin Geisler,Peter Kratzer###

Spincaloric properties of epitaxial Co$_2$MnSi/MgO/Co$_2$MnSi magnetic tunnel junctions. The electronic transport and spincaloric properties of epitaxial magnetic
tunnel junctions with half-metallic Co$_2$MnSi Heusler electrodes, MgO
tunneling barriers, and different interface terminations are investigated by
using first-principles calculations. A new approach to spincaloric properties
is presented that circumvents the linear response approximation inherent in the
Seebeck coefficient and compared to the method of Sivan and Imry. This approach
supports two different temperatures in the two electrodes and provides the
exact current and/or voltage response of the system. Moreover, it accounts for
temperature-dependent chemical potentials in the electrodes and finite-bias
effects. We find that especially the former are important for obtaining
qualitatively correct results, even if the variations of the chemical
potentials are small. It is shown how the spincaloric properties can be
tailored by the choice of the growth conditions. We find a large effective and
spin-dependent Seebeck coefficient of $-65$ $\mu$V/K at room temperature for
the purely Co-terminated interface. We suggest to use such interfaces in
thermally operated magnetoresistive random access memory modules, which exploit
the magneto-Seebeck effect, to maximize the thermally induced readout voltage.

###Half-metallic ferromagnets for magnetic tunnel junctions|Phivos Mavropoulos,Marjana Lezaic,Stefan Bluegel###

Half-metallic ferromagnets for magnetic tunnel junctions. Using theoretical arguments, we show that, in order to exploit half-metallic
ferromagnets in tunneling magnetoresistance (TMR) junctions, it is crucial to
eliminate interface states at the Fermi level within the half-metallic gap;
contrary to this, no such problem arises in giant magnetoresistance elements.
Moreover, based on an a priori understanding of the electronic structure, we
propose an antiferromagnetically coupled TMR element, in which interface states
are eliminated, as a paradigm of materials design from first principles. Our
conclusions are supported by ab-initio calculations.

###Spinel ferrites: old materials bring new opportunities for spintronics|Ulrike Lueders,Agnes Barthelemy,Manuel Bibes,Karim Bouzehouane,Stephane Fusil,Eric Jacquet,Jean-Pierre Contour,Jean-Francois Bobo,Josep Fontcuberta,Albert Fert###

Spinel ferrites: old materials bring new opportunities for spintronics. Over the past few years, intensive studies of ultrathin epitaxial films of
perovskite oxides have often revealed exciting properties like giant
magnetoresistive tunnelling and electric field effects. Spinel oxides appear as
even more versatile due to their more complex structure and the resulting many
degrees of freedom. Here we show that the epitaxial growth of nanometric
NiFe2O4 films onto perovskite substrates allows the stabilization of novel
ferrite phases with properties dramatically differing from bulk ones. Indeed,
NiFe2O4 films few nanometres thick have a saturation magnetization at least
twice that of the bulk compound and their resistivity can be tuned by orders of
magnitude, depending on the growth conditions. By integrating such thin NiFe2O4
layers into spin-dependent tunnelling heterostructures, we demonstrate that
this versatile material can be useful for spintronics, either as a conductive
electrode in magnetic tunnel junctions or as a spin-filtering insulating
barrier in the little explored type of tunnel junction called spin-filter. Our
findings are thus opening the way for the realisation of monolithic spintronics
architectures integrating several layers of a single material, where the layers
are functionalised in a controlled manner.

###Synthetic antiferromagnet with Heusler alloy Co2FeAl ferromagnetic layers|X. G. Xu,D. L. Zhang,X. Q. Li,J. Bao,Y. Jiang###

Synthetic antiferromagnet with Heusler alloy Co2FeAl ferromagnetic layers. Heusler alloy Co2FeAl was employed as ferromagnetic layers in
Co2FeAl/Ru/Co2FeAl synthetic antiferromagnet structures. The experimental
results show that the structure with a Ru thickness of 0.45 nm takes on
strongly antiferromagnetic coupling, which maintains up to 150 oC annealing for
1 hour. The structure has a very low saturation magnetization Ms of 425 emu/cc,
a low switching field Hsw of 4.3 Oe and a high saturation field Hs of 5257 Oe
at room temperature, which are favorable for application in ultrahigh density
magnetic read heads or other magnetic memory devices. XRD study testifies that
the as-deposited Co2FeAl film is in B2 phase. Therefore Heusler alloys can be
used to fabricate SyAF and it is possible to make "all-Heusler" spin-valves or
magnetic tunneling junctions with better magnetic switching properties and high
magnetoresistance.

###Novel Majorana mode and magnetoresistance in ferromagnetic superconducting topological insulator|Hadi Goudarzi,Maryam Khezerlou,Samin Asgarifar###

Novel Majorana mode and magnetoresistance in ferromagnetic superconducting topological insulator. Among the potential applications of topological insulators, we investigate
theoretically the effect of coexistence of proximity-induced ferromagnetism and
superconductivity on the surface states of 3-dimensional topological insulator,
where the superconducting electron-hole excitations can be significantly
affected by the magnetization of ferromagnetic order. We find that, Majorana
mode energy, as a verified feature of TI F/S structure, along the interface
sensitively depends on the magnitude of magnetization $m_{zfs}$ in FS region,
while its slope in perpendicular incidence presents steep and no change. Since
the superconducting gap is renormalized by a factor $\eta(m_{zfs})$, hence
Andreev reflection is more or less suppressed, and, in particular, resulting
subgap tunneling conductance is more sensitive to the magnitude of
magnetizations in FS and F regions. Furthermore, an interesting scenario
happens at the antiparallel configuration of magnetizations $m_{zf}$ and
$m_{zfs}$ resulting in magnetoresistance in N/F/FS junction, which can be
controlled and decreased by tuning the magnetization magnitude in FS region.

###A Low Temperature Functioning CoFeB/MgO Based Perpendicular Magnetic Tunnel Junction for Cryogenic Nonvolatile Random Access Memory|Lili Lang,Yujie Jiang,Fei Lu,Cailu Wang,Yizhang Chen,Andrew D. Kent,Li Ye###

A Low Temperature Functioning CoFeB/MgO Based Perpendicular Magnetic Tunnel Junction for Cryogenic Nonvolatile Random Access Memory. We investigated the low temperature performance of CoFeB/MgO based
perpendicular magnetic tunnel junctions (pMTJs) by characterizing their
quasi-static switching voltage, high speed pulse write error rate and endurance
down to 9 K. pMTJ devices exhibited high magnetoresistance (>120%) and reliable
(error rate<10-4) bi-directional switching with 2 to 200 ns voltage pulses. The
endurance of the devices at 9 K surpassed that at 300 K by three orders of
magnitude under the same write conditions, functioning for more than 10^12
cycles with 10 ns write pulses. The critical switching voltage at 9 K was
observed to increase by 33% to 93%, depending on pulse duration, compared to
that at 350 K. Ferromagnetic resonance and magnetization measurements on
blanket pMTJ film stacks suggest that the increased switching voltage is
associated with an increase in effective magnetic anisotropy and magnetization
of free layer with decreasing temperature. Our work demonstrates that CoFeB/MgO
based pMTJs have great potential to enable cryogenic MRAM and that their low
temperature magnetization and effective magnetic anisotropy can be further
optimized to lower operating power and improve endurance.

###Spin-orbit torque switching of magnetic tunnel junctions for memory application|Viola Krizakova,Manu Perumkunnil,Sebastien Couet,Pietro Gambardella,Kevin Garello###

Spin-orbit torque switching of magnetic tunnel junctions for memory application. Spin-orbit torques (SOT) provide a versatile tool to manipulate the
magnetization of diverse classes of materials and devices using electric
currents, leading to novel spintronic memory and computing approaches. In
parallel to spin transfer torques (STT), which have emerged as a leading
non-volatile memory technologie, SOT broaden the scope of current-induced
magnetic switching to applications that run close to the clock speed of the
central processing unit and unconventional computing architectures. In this
paper, we review the fundamental characteristics of SOT and their use to switch
magnetic tunnel junction (MTJ) devices, the elementary unit of the
magnetoresistive random access memory (MRAM). In the first part, we illustrate
the physical mechanisms that drive the SOT and magnetization reversal in
nanoscale structures. In the second part, we focus on the SOT-MTJ cell. We
discuss the anatomy of the MTJ in terms of materials and stack development,
summarize the figures of merit for SOT switching, review the field-free
operation of perpendicularly magnetized MTJs, and present options to combine
SOT, STT and voltage-gate assisted switching. In the third part, we consider
SOT-MRAMs in the perspective of circuit integration processes, introducing
considerations on scaling and performance, as well as macro-design
architectures. We thus bridge the fundamental description of SOT-driven
magnetization dynamics with an application-oriented perspective, including
device and system-level considerations, goals, and challenges.

###Spin currents and magnetoresistance of graphene-based magnetic junctions|Alireza Saffarzadeh,Mahdi Ghorbani Asl###

Spin currents and magnetoresistance of graphene-based magnetic junctions. Using the tight-binding approximation and the nonequilibrium Green's function
approach, we investigate the coherent spin-dependent transport in planar
magnetic junctions consisting of two ferromagnetic (FM) electrodes separated by
a graphene flake (GF) with zigzag or armchair interfaces. It is found that the
electron conduction strongly depends on the geometry of contact between the GF
and the FM electrodes. In the case of zigzag interfaces, the junction
demonstrates a spin-valve effect with high magnetoresistance (MR) ratios and
shows negative differential resistance features for a single spin channel at
positive gate voltage. In the case of armchair interfaces, the current-voltage
characteristics behave linearly at low bias voltages and hence, both spin
channels are in on state with low MR ratios.

###New memory devices based on the proton transfer process|Malgorzata Wierzbowska###

New memory devices based on the proton transfer process. Memory devices operating due to the fast proton transfer (PT) process are
proposed by means of the first-principles calculations. Writing an information
is performed using the electrostatic potential of the scanning tunneling
microscopy (STM). Reading an information is based on the effect of the local
magnetization induced at the zigzag graphene nanoribbon (Z-GNR) edge -
saturated with oxygen or the hydroxy group - and can be realized with the use
of the giant magnetoresistance (GMR), magnetic tunnel junction (MTJ) or
spin-transfer torque (STT) devices. The energetic barriers for the hop-forward
and -backward processes can be tuned by the distance and potential of the STM
tip. Thus, enabling to tailor the non-volatile logic states. The proposed
system enables very dense packing of the logic cells and could be used in the
random access and flash memory devices.

###Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2|Yuji Yamasaki,Rai Moriya,Miho Arai,Satoru Masubuchi,Sunseng Pyon,Tsuyoshi Tamegai,Keiji Ueno,Tomoki Machida###

Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2. Ferromagnetic van der Waals (vdW) materials are in demand for spintronic
devices with all-two-dimensional-materials heterostructures. Here, we
demonstrate mechanical exfoliation of magnetic-atom-intercalated transition
metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such
intercalated materials were thought difficult to exfoliate. Magnetotransport in
exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering
below its Curie temperature TC ~ 110 K as well as strong in-plane magnetic
anisotropy; these are identical to its bulk properties. Further, van der Waals
heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet
Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated
heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide
tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing
possible spin injection and detection with these exfoliatable ferromagnetic
materials through the vdW junction.

###Circuit-Level Evaluation of the Generation of Truly Random Bits with Superparamagnetic Tunnel Junctions|Damir Vodenicarevic,Nicolas Locatelli,Alice Mizrahi,Tifenn Hirtzlin,Joseph S. Friedman,Julie Grollier,Damien Querlioz###

Circuit-Level Evaluation of the Generation of Truly Random Bits with Superparamagnetic Tunnel Junctions. Many emerging alternative models of computation require massive numbers of
random bits, but their generation at low energy is currently a challenge. The
superparamagnetic tunnel junction, a spintronic device based on the same
technology as spin torque magnetoresistive random access memory has recently
been proposed as a solution, as this device naturally switches between two easy
to measure resistance states, due only to thermal noise. Reading the state of
the junction naturally provides random bits, without the need of write
operations. In this work, we evaluate a circuit solution for reading the state
of superparamagnetic tunnel junction. We see that the circuit may induce a
small read disturb effect for scaled superparamagnetic tunnel junctions, but
this effect is naturally corrected in the whitening process needed to ensure
the quality of the generated random bits. These results suggest that
superparamagnetic tunnel junctions could generate truly random bits at 20
fJ/bit, including overheads, orders of magnitudes below CMOS-based solutions.

###Spin transistor built on 2D van der Waals heterostructures|Shengwei Jiang,Lizhong Li,Zefang Wang,Jie Shan,Kin Fai Mak###

Spin transistor built on 2D van der Waals heterostructures. Spin transistors (whose on-off operation is achieved by
electric-field-controlled spin orientation 1), if realized, can revolutionize
modern electronics through the implementation of a faster and a more
energy-efficient performance as well as non-volatile data storage 2, 3. The
original proposal by Datta and Das 1 that relies on electric-field-controlled
spin precession in a semiconductor channel faces significant challenges
including inefficient spin injection, spin relaxation and spread of the spin
precession angle 4, 5. Recent demonstration of electric-field switching of
magnetic order 6-8 and spin filtering 9-12 in two-dimensional magnetic
insulator CrI3 has inspired a new operational principle for spin transistors.
Here we demonstrate spin field-effect transistors based on dual-gated
graphene/CrI3 tunnel junctions. These devices show an ambipolar transistor
behavior and tunnel magnetoresistance widely tunable by gating when the CrI3
magnetic tunnel barrier undergoes an antiferromagnetic-ferromagnetic spin-flip
transition. Under a constant magnetic bias in the vicinity of the spin-flip
transition, the gate voltage can repeatedly alter the device between a high and
a low conductance state with a large hysteresis. This new spin transistor
concept based on the electric-field-controlled spin-flip transition in the
magnetic tunnel barrier is immune to interface imperfections and allows spin
injection, control and detection in a single device.

###Seebeck Effect in Magnetic Tunnel Junctions|Marvin Walter,Jakob Walowski,Vladyslav Zbarsky,Markus Münzenberg,Markus Schäfers,Daniel Ebke,Günter Reiss,Andy Thomas,Patrick Peretzki,Michael Seibt,Jagadeesh S. Moodera,Michael Czerner,Michael Bachmann,Christian Heiliger###

Seebeck Effect in Magnetic Tunnel Junctions. Creating temperature gradients in magnetic nanostructures has resulted in a
new research direction, i.e., the combination of magneto- and thermoelectric
effects. Here, we demonstrate the observation of one important effect of this
class: the magneto-Seebeck effect. It is observed when a magnetic configuration
changes the charge based Seebeck coefficient. In particular, the Seebeck
coefficient changes during the transition from a parallel to an antiparallel
magnetic configuration in a tunnel junction. In that respect, it is the analog
to the tunneling magnetoresistance. The Seebeck coefficients in parallel and
antiparallel configuration are in the order of the voltages known from the
charge-Seebeck effect. The size and sign of the effect can be controlled by the
composition of the electrodes' atomic layers adjacent to the barrier and the
temperature. Experimentally, we realized 8.8 % magneto-Seebeck effect, which
results from a voltage change of about -8.7 {\mu}V/K from the antiparallel to
the parallel direction close to the predicted value of -12.1 {\mu}V/K.

###Tunnel magnetoresistance angular and bias dependence enabling tuneable wireless communication|Ewa Kowalska,Akio Fukushima,Volker Sluka,Ciarán Fowley,Attila Kákay,Yuriy Aleksandrov,Jürgen Lindner,Jürgen Fassbender,Shinji Yuasa,Alina M. Deac###

Tunnel magnetoresistance angular and bias dependence enabling tuneable wireless communication. Spin-transfer torques (STTs) can be exploited in order to manipulate the
magnetic moments of nanomagnets, thus allowing for new consumer-oriented
devices to be designed. Of particular interest here are tuneable
radio-frequency (RF) oscillators for wireless communication. Currently, the
structure that maximizes the output power is an Fe/MgO/Fe-type magnetic tunnel
junction (MTJ) with a fixed layer magnetized in the plane of the layers and a
free layer magnetized perpendicular to the plane. This structure allows for
most of the tunnel magnetoresistance (TMR) to be converted into output power.
Here, we experimentally and theoretically demonstrate that the main mechanism
sustaining steady-state precession in such structures is the angular dependence
of the magnetoresistance. The TMR of such devices is known to exhibit a
broken-linear dependence versus the applied bias. Our results show that the TMR
bias dependence effectively quenches spin-transfer-driven precession and
introduces a non-monotonic frequency dependence at high applied currents. Thus
we expect the bias dependence of the TMR to have an even more dramatic effect
in MTJs with Mn-Ga-based free layers, which could be used to design wireless
oscillators extending towards the THz gap, but have been experimentally shown
to exhibit a non-trivial TMR bias dependence.

###Bias dependent inversion of tunneling magnetoresistance in Fe/GaAs/Fe tunnel junctions|J. Moser,M. Zenger,C. Gerl,D. Schuh,R. Meier,P. Chen,G. Bayreuther,W. Wegscheider,D. Weiss,C. -H. Lai,R. -T. Huang,M. Kosuth,H. Ebert###

Bias dependent inversion of tunneling magnetoresistance in Fe/GaAs/Fe tunnel junctions. We investigated spin dependent transport through Fe/GaAs/Fe tunnel junctions.
The tunneling magnetoresistance effect (TMR) was probed for different types of
Fe/GaAs interfaces. For interfaces cleaned by hydrogen plasma the TMR effect is
increased and observable at room temperature. If an epitaxial Fe/GaAs(001)
interface is involved, the tunnel junction exhibits a bias dependent inversion
of the TMR effect. This is a first experimental signature for band structure
effects at a Fe/GaAs interface and relevant for spin injection experiments.

###Suppression of superconductivity due to spin imbalance in Co/Al/Co single electron transistor|Jan Johansson,Mattias Urech,David Haviland,V. Korenivski###

Suppression of superconductivity due to spin imbalance in Co/Al/Co single electron transistor. Transport properties of ferromagnetic/non-magnetic/ferromagnetic single
electron transistors are investigated as a function of external magnetic field,
temperature, bias and gate voltage. By designing the magnetic electrodes to
have different switching fields, a two-mode device is realized having two
stable magnetization states, with the electrodes aligned in parallel and
antiparallel. Magnetoresistance of approximately 100% is measured in
Co/AlO$_{X}$/Al/AlO$_{X}$/Co double tunnel junction spin valves at low bias,
with the Al spacer in the superconducting state. The effect is substantially
reduced at high bias and temperatures above the $T_{C}$ of the Al. The
experimental results are interpreted as due to spin imbalance of charge
carriers resulting in suppression of the superconducting gap of the Al island.

###Separating read and write units in multiferroic devices|Kuntal Roy###

Separating read and write units in multiferroic devices. Strain-mediated multiferroic composites, i.e., piezoelectric-magnetostrictive
heterostructures, hold profound promise for energy-efficient computing in
beyond Moore's law era. While reading a bit of information stored in the
magnetostrictive nanomagnets using a magnetic tunnel junction (MTJ), a material
selection issue crops up since magnetostrictive materials in general cannot be
utilized as the free layer of the MTJ. This is an important issue since we need
to achieve a high magnetoresistance for technological applications. We show
here that magnetically coupling the magnetostrictive nanomagnet and the free
layer e.g., utilizing the magnetic dipole coupling between them can circumvent
this issue. By solving stochastic Landau-Lifshitz-Gilbert equation of
magnetization dynamics in the presence of room-temperature thermal
fluctuations, we show that such design can eventually lead to a superior
energy-delay product.

###A Compact Model for Scalable MTJ Simulation|Fernando García-Redondo,Pranay Prabhat,Mudit Bhargava,Cyrille Dray###

A Compact Model for Scalable MTJ Simulation. This paper presents a physics-based modeling framework for the analysis and
transient simulation of circuits containing Spin-Transfer Torque (STT) Magnetic
Tunnel Junction (MTJ) devices. The framework provides the tools to analyze the
stochastic behavior of MTJs and to generate Verilog-A compact models for their
simulation in large VLSI designs, addressing the need for an industry-ready
model accounting for real-world reliability and scalability requirements.
Device dynamics are described by the Landau-Lifshitz-Gilbert-Slonczewsky
(s-LLGS ) stochastic magnetization considering Voltage-Controlled Magnetic
Anisotropy (VCMA) and the non-negligible statistical effects caused by thermal
noise. Model behavior is validated against the OOMMF magnetic simulator and its
performance is characterized on a 1-Mb 28 nm Magnetoresistive-RAM (MRAM) memory
product.

###Exotic spintronic properties of transition-metal monolayers on graphyne|Xiaoxiong Ren,Junsheng Huang,Ping Li,Yun Zhang,Zhi-Xin Guo###

Exotic spintronic properties of transition-metal monolayers on graphyne. The recent discovery of two-dimensional (2D) magnetic materials which are
compound of transition metal (TM) with other elements, has opened new avenues
for basic research on low-dimensional magnetism and potential applications in
spintronics. To further explore new 2D magnets of pure TM is thus of an
interesting topic. Based on the first-principles calculations, here we propose
a strategy of obtaining monolayer TM magnets, i.e., depositing TM atoms on
graphyne (Gy) which has proper hexagonal hollow geometry. We find that TM
monolayer with perfect hexagonal geometry can be formed on Gy. The TM monolayer
exhibits a wealth of physical properties in dependence of TM species, such as
ferromagnetic and antiferromagnetic ground states, as well as intriguing
semimetal and half-metal characteristics. We also find that the half-metal
characteristics makes the monolayer TM have great potential applications in the
horizontal magnetic tunnel junction (MTJ) devices, where the tunneling
magnetoresistance can reach as high as 850000%. Our results provide a new
framework for obtaining 2D magnets with outstanding spintronic properties.

###Time-Dependent Spintronic Transport and Current-Induced Spin Transfer Torque in Magnetic Tunnel Junctions|Zhen-Gang Zhu,Gang Su,Qing-Rong Zheng,Biao Jin###

Time-Dependent Spintronic Transport and Current-Induced Spin Transfer Torque in Magnetic Tunnel Junctions. The responses of the electrical current and the current-induced spin transfer
torque (CISTT) to an ac bias in addition to a dc bias in a magnetic tunnel
junction are investigated by means of the time-dependent nonquilibrium Green
function technique. The time-averaged current (time-averaged CISTT) is
formulated in the form of a summation of dc current (dc CISTT) multiplied by
products of Bessel functions with the energy levels shifted by $m\hbar \omega
_{0}$. The tunneling current can be viewed as to happen between the photonic
sidebands of the two ferromagnets. The electrons can pass through the barrier
easily under high frequencies but difficultly under low frequencies. The tunnel
magnetoresistance almost does not vary with an ac field. It is found that the
spin transfer torque, still being proportional to the electrical current under
an ac bias, can be changed by varying frequency. Low frequencies could yield a
rapid decrease of the spin transfer torque, while a large ac signal leads to
both decrease of the electrical current and the spin torque. If only an ac bias
is present, the spin transfer torque is sharply enhanced at the particular
amplitude and frequency of the ac bias. A nearly linear relation between such
an amplitude and frequency is observed.

###Magnetic coherent tunnel junctions with periodic grating barrier|Henan Fang,Mingwen Xiao,Wenbin Rui,Jun Du,Zhikuo Tao###

Magnetic coherent tunnel junctions with periodic grating barrier. A new spintronic theory has been developed for the magnetic tunnel junction
(MTJ) with single-crystal barrier. The barrier will be treated as a diffraction
grating with intralayer periodicity, the diffracted waves of tunneling
electrons thus contain strong coherence, both in charge and especially in spin.
The theory can answer the two basic problems present in MgO-based MTJs: (1) Why
does the tunneling magnetoresistance (TMR) oscillate with the barrier
thickness? (2) Why is the TMR still far away from infinity when the two
electrodes are both half-metallic? Other principal features of TMR can also be
explained and reproduced by the present work. It also provides possible ways to
modulate the oscillation of TMR, and to enhance TMR so that it can tend to
infinity. Within the theory, the barrier, as a periodic diffraction grating,
can get rid of the confinement in width, it can vary from nanoscale to
microscale. Based on those results, a future-generation MTJ is proposed where
the three pieces can be fabricated separately and then assembled together, it
is especially appropriate for the layered materials, e.g., MoS2 and graphite,
and most feasible for industries.

###Field-free Magnetization Switching by Utilizing the Spin Hall Effect and Interlayer Exchange Coupling of Iridium|Yang Liu,Bing Zhou,Jian-Gang Zhu###

Field-free Magnetization Switching by Utilizing the Spin Hall Effect and Interlayer Exchange Coupling of Iridium. Magnetization switching by spin-orbit torque (SOT) via spin Hall effect
represents as a competitive alternative to that by spin-transfer torque (STT)
used for magnetoresistive random access memory (MRAM), as it does not require
high-density current to go through the tunnel junction. For perpendicular MRAM,
however, SOT driven switching of the free layer requires an external in-plane
field, which poses limitation for viability in practical applications. Here we
demonstrate field-free magnetization switching of a perpendicular magnet by
utilizing an Iridium (Ir) layer. The Ir layer not only provides SOTs via spin
Hall effect, but also induce interlayer exchange coupling with an in-plane
magnetic layer that eliminates the need for the external field. Such dual
functions of the Ir layer allows future build-up of magnetoresistive stacks for
memory and logic applications. Experimental observations show that the SOT
driven field-free magnetization reversal is characterized as domain nucleation
and expansion. Micromagnetic modeling is carried out to provide in-depth
understanding of the perpendicular magnetization reversal process in the
presence of an in-plane exchange coupling field.

###A proper ballistic calculation of tunneling conductance for real junctions|P. M. Levy,K. Wang,P. H. Dederichs,C. Heide,S. Zhang,L. Szunyogh,P. Weinberger###

A proper ballistic calculation of tunneling conductance for real junctions. Employing an ab initio Screened Korringa-Kohn-Rostoker (SKKR) band structure
method for a metal-vacuum-metal junction, we find that the tunnel conductance
is different when it is calculated across the barrier and far from it. We
attribute this difference to an artefact of the ballistic approach which
overestimates the role of specular reflections, and its inability to pick up
contributions from localized interface states. To reconcile the ballistic
approach with experiment, we propose that the tunnel conductance should be
calculated as if it is measured directly across the barrier. In this case the
predicted tunneling magnetoresistance is larger.

###Temperature dependences of resistivity and magnetoresistivity for half-metallic ferromagnets|V. Yu. Irkhin,M. I. Katsnelson###

Temperature dependences of resistivity and magnetoresistivity for half-metallic ferromagnets. Peculiarities of transport properties of three- and two-dimensional
half-metallic ferromagnets are investigated, which are connected with the
absence of spin-flip scattering processes. The temperature and magnetic field
dependences of resistivity in various regimes are calculated. The resistivity
is proportional to T^{9/2} for T<T* and to T^{7/2} for T>T*, T* being the
crossover temperature for longitudinal scattering processes. The latter scale
plays also an important role in magnetoresistance. The contribution of
non-quasiparticle (incoherent) states to the transport properties is discussed.
It is shown that they can dominate in the temperature dependence of the
impurity-induced resistivity and in the tunnel junction conductivity.

###High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins|A. M. Bratkovsky,V. V. Osipov###

High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins. New mechanism of magnetoresistance, based on tunneling-emission of spin
polarized electrons from ferromagnets (FM) into semiconductors (S) and
precession of electron spin in the semiconductor layer under external magnetic
field, is described. The FM-S-FM structure is considered, which includes very
thin heavily doped (delta-doped) layers at FM-S interfaces. At certain
parameters the structure is highly sensitive at room-temperature to variations
of the field with frequencies up to 100 GHz. The current oscillates with the
field, and its relative amplitude is determined only by the spin polarizations
of FM-S junctions at relatively large bias voltage.

###Laser microscopy of tunneling magnetoresistance in manganite grain-boundary junctions|M. Wagenknecht,H. Eitel,T. Nachtrab,J. B. Philipp,R. Gross,R. Kleiner,D. Koelle###

Laser microscopy of tunneling magnetoresistance in manganite grain-boundary junctions. Using low-temperature scanning laser microscopy we directly image electric
transport in a magnetoresistive element, a manganite thin film intersected by a
grain boundary (GB). Imaging at variable temperature allows reconstruction and
comparison of the local resistance vs temperature for both, the manganite film
and the GB. Imaging at low temperature also shows that the GB switches between
different resistive states due to the formation and growth of magnetic domains
along the GB. We observe different types of domain wall growth; in most cases a
domain wall nucleates at one edge of the bridge and then proceeds towards the
other edge.

###Anisotropic magnetoresistance in nanocontacts|D. Jacob,J. Fernandez-Rossier,J. J. Palacios###

Anisotropic magnetoresistance in nanocontacts. We present ab initio calculations of the evolution of anisotropic
magnetoresistance (AMR) in Ni nanocontacts from the ballistic to the tunnel
regime. We find an extraordinary enhancement of AMR, compared to bulk, in two
scenarios. In systems without localized states, like chemically pure break
junctions, large AMR only occurs if the orbital polarization of the current is
large, regardless of the anisotropy of the density of states. In systems that
display localized states close to the Fermi energy, like a single electron
transistor with ferromagnetic electrodes, large AMR is related to the variation
of the Fermi energy as a function of the magnetization direction.

###Robust spin-transfer torque and magnetoresistance in non-collinear antiferromagnetic junctions|Srikrishna Ghosh,Aurelien Manchon,Jakub Železný###

Robust spin-transfer torque and magnetoresistance in non-collinear antiferromagnetic junctions. Ferromagnetic spin-valves and tunneling junctions are crucial for spintronics
applications and are one of the most fundamental spintronics devices. Motivated
by the potential unique advantages of antiferromagnets for spintronics, we
theoretically study here junctions built out of non-collinear antiferromagnets.
We demonstrate a large and robust magnetoresistance and spin-transfer torque
capable of ultrafast switching between parallel and anti-parallel states of the
junction. In addition, we show that the non-collinear order results in a
spin-transfer torque that is in several key aspects different from the
spin-transfer torque in ferromagnetic junctions.

###Superconducting contacts to a monolayer semiconductor|M. Ramezani,I. Correa Sampaio,K. Watanabe,T. Taniguchi,C. Schönenberger,A. Baumgartner###

Superconducting contacts to a monolayer semiconductor. We demonstrate superconducting vertical interconnect access (VIA) contacts to
a monolayer of molybdenum disulfide (MoS$_2$), a layered semiconductor with
highly relevant electronic and optical properties. As a contact material we use
MoRe, a superconductor with a high critical magnetic field and high critical
temperature. The electron transport is mostly dominated by a single
superconductor/normal conductor junction with a clear superconductor gap. In
addition, we find MoS$_2$ regions that are strongly coupled to the
superconductor, resulting in resonant Andreev tunneling and junction dependent
gap characteristics, suggesting a superconducting proximity effect.
Magnetoresistance measurements show that the bandstructure and the high
intrinsic carrier mobility remain intact in the bulk of the MoS$_2$. This type
of VIA contact is applicable to a large variety of layered materials and
superconducting contacts, opening up a path to monolayer semiconductors as a
platform for superconducting hybrid devices.

###Resonant spin transfer torque nano-oscillators|Abhishek Sharma,Ashwin A Tulapurkar,Bhaskaran Muralidharan###

Resonant spin transfer torque nano-oscillators. Spin transfer torque nano-oscillators are potential candidates for replacing
the traditional inductor based voltage controlled oscillators in modern
communication devices. Typical oscillator designs are based on trilayer
magnetic tunnel junctions which are disadvantaged by low power outputs and poor
conversion efficiencies. In this letter, we theoretically propose to use
resonant spin filtering in pentalayer magnetic tunnel junctions as a possible
route to alleviate these issues and present device designs geared toward a high
microwave output power and an efficient conversion of the d.c. input power. We
attribute these robust qualities to the resulting non-trivial spin current
profiles and the ultra high tunnel magnetoresistance, both arising from
resonant spin filtering. The device designs are based on the nonequilibrium
Green's function spin transport formalism self-consistently coupled with the
stochastic Landau-Lifshitz-Gilbert-Slonczewski's equation and the Poisson's
equation. We demonstrate that the proposed structures facilitate oscillator
designs featuring a large enhancement in microwave power of around $775\%$ and
an efficiency enhancement of over $1300\%$ in comparison with typical trilayer
designs. We also rationalize the optimum operating regions via an analysis of
the dynamic and static device resistances. This work sets stage for pentalyer
spin transfer torque nano-oscillator device designs that extenuate most of the
issues faced by the typical trilayer designs.

###Heavily Damped Precessional Switching with Very Low Write-error Rate in Elliptical-cylinder Magnetic Tunnel Junction|Rie Matsumoto,Shinji Yuasa,Hiroshi Imamura###

Heavily Damped Precessional Switching with Very Low Write-error Rate in Elliptical-cylinder Magnetic Tunnel Junction. Voltage-induced dynamic switching in magnetic tunnel junctions (MTJs) is a
writing technique for voltage-controlled magnetoresistive random access memory
(VCMRAM), which is expected to be an ultimate non-volatile memory with
ultra-low power consumption. In conventional dynamic switching, the width of
sub-nanosecond write voltage pulses must be precisely controlled to achieve a
sufficiently low write-error rate (WER). This very narrow tolerance of pulse
width is the biggest technical difficulty in developing VCMRAM. Heavily damped
precessional switching is a writing scheme for VCMRAM with a substantially high
tolerance of pulse width although the minimum WER has been much higher than
that of conventional dynamic switching with an optimum pulse width. In this
study, we theoretically investigate the effect of MTJ shape and the direction
of the applied magnetic field on the WER of heavily damped precessional
switching. The results show that the WER in elliptical-cylinder MTJ can be
several orders of magnitude smaller than that in usual circular-cylinder MTJ
when the external magnetic field is applied parallel to the minor axis of the
ellipse. The reduction in WER is due to the fact that the demagnetization field
narrows the component of the magnetization distribution perpendicular to the
plane direction immediately before the voltage is applied.

###Gate voltage controlled electronic transport through a ferromagnet/normal/ferromagnet junction on the surface of a topological insulator|K. H. Zhang,Z. C. Wang,Q. R. Zheng,G. Su###

Gate voltage controlled electronic transport through a ferromagnet/normal/ferromagnet junction on the surface of a topological insulator. We investigate the electronic transport properties of a
ferromagnet/normal/ferromagnet junction on the surface of a topological
insulator with a gate voltage exerted on the normal segment. It is found that
the conductance oscillates with the width of normal segment and gate voltage,
and the maximum of conductance gradually decreases while the minimum of
conductance approaches zero as the width increases. The conductance can be
controlled by tuning the gate voltage like a spin field-effect transistor. It
is found that the magnetoresistance ratio can be very large, and can also be
negative owing to the anomalous transport. In addition, when there exists a
magnetization component in the surface plane, it is shown that only the
component parallel to the junction interface has an influence on the
conductance.

###Extrinsic Magnetotransport Phenomena in Ferromagnetic Oxides|Michael Ziese###

Extrinsic Magnetotransport Phenomena in Ferromagnetic Oxides. This review is focused on extrinsic magnetotransport effects in ferromagnetic
oxides. It consists of two parts; the second part is devoted to an overview of
experimental data and theoretical models for extrinsic magnetotransport
phenomena. Here a critical discussion of domain-wall scattering is given.
Results on surfacial and interfacial magnetism in oxides are presented.
Spin-polarized tunnelling in ferromagnetic junctions is reviewed and
grain-boundary magnetoresistance is interpreted within a model of
spin-polarized tunnelling through natural oxide barriers. The situation in
ferromagnetic oxides is compared with data and models for conventional
ferromagnets. The first part of the review summarizes basic material
properties, especially data on the spin-polarization and evidence for
half-metallicity. Furthermore, intrinsic conduction mechanisms are discussed.
An outlook on the further development of oxide spin-electronics concludes this
review.

###Spin effects in electron tunnelling through a quantum dot coupled to non-collinearly polarized ferromagnetic leads|W. Rudzinski,J. Barnas,R. Swirkowicz,M. Wilczynski###

Spin effects in electron tunnelling through a quantum dot coupled to non-collinearly polarized ferromagnetic leads. Spin-dependent transport through an interacting single-level quantum dot
coupled to ferromagnetic leads with non-collinear magnetizations is analyzed
theoretically. The transport properties and average spin of the dot are
investigated within the nonequilibrium Green function technique based on the
equation of motion in the Hartree-Fock approximation. Numerical results show
that Coulomb correlations on the dot and strong spin polarization of the leads
significantly enhance precession of the average dot spin around the effective
molecular field created by the external electrodes. Moreover, they also show
that spin precession may lead to negative differential conductance in the
voltage range between the two relevant threshold voltages. Nonmonotonous
angular variation of electric current and change in sign of the tunnel
magnetoresistance are also found. It is also shown that the diode-like behavior
in asymmetrical junctions with one electrode being half-metallic is
significantly reduced in noncollinear configurations.

###Interplay between Aharonov-Bohm interference and parity selective tunneling in zigzag graphene nanoribbon rings|Viet-Hung Nguyen,Yann-Michel Niquet,Philippe Dollfus###

Interplay between Aharonov-Bohm interference and parity selective tunneling in zigzag graphene nanoribbon rings. We report a numerical study on Aharonov-Bohm (AB) effect and parity selective
tunneling in pn junctions based on zigzag graphene nanoribbon rings. We find
that when applying a magnetic field to the ring, the AB interference can
reverse the parity symmetry of incoming waves and hence can strongly modulate
the parity selective transmission through the system. Therefore, the
transmission between two states of different parity exhibits the AB
oscillations with a \pi-phase shift, compared to the case of states of same
parity. On this basis, it is shown that interesting effects such as giant (both
positive and negative) magnetoresistance and strong negative differential
conductance can be achieved in this structure. Our study thus presents a new
property of the AB interference, which could be helpful to further understand
the transport properties of graphene mesoscopic-systems.

###Structural and magneto-transport characterization of Co_2Cr_xFe_(1-x)Al Heusler alloy films|A. D. Rata,H. Braak,D. E. Buergler,S. Cramm,C. M. Schneider###

Structural and magneto-transport characterization of Co_2Cr_xFe_(1-x)Al Heusler alloy films. We investigate the structure and magneto-transport properties of thin films
of the Co_2Cr_xFe_(1-x)Al full-Heusler compound, which is predicted to be a
half-metal by first-principles theoretical calculations. Thin films are
deposited by magnetron sputtering at room temperature on various substrates in
order to tune the growth from polycrystalline on thermally oxidized Si
substrates to highly textured and even epitaxial on MgO(001) substrates,
respectively. Our Heusler films are magnetically very soft and ferromagnetic
with Curie temperatures up to 630 K. The total magnetic moment is reduced
compared to the theoretical bulk value, but still comparable to values reported
for films grown at elevated temperature. Polycrystalline Heusler films combined
with MgO barriers are incorporated into magnetic tunnel junctions and yield 37%
magnetoresistance at room temperature.

###Neutron scattering study of magnetic phase separation in nanocrystalline La$_{5/8}$Ca$_{3/8}$MnO$_3$|Chetan Dhital,Clarina de la Cruz,C. Opeil,A. Treat,K. F. Wang,J. -M. Liu,Z. F. Ren,Stephen D. Wilson###

Neutron scattering study of magnetic phase separation in nanocrystalline La$_{5/8}$Ca$_{3/8}$MnO$_3$. We demonstrate that magnetic phase separation and competing spin order in the
colossal magnetoresistive (CMR) manganites can be directly explored via tuning
strain in bulk samples of nanocrystalline La$_{1-x}$Ca$_x$MnO$_3$. Our results
show that strain can be reversibly frozen into the lattice in order to
stabilize coexisting antiferromagnetic domains within the nominally
ferromagnetic metallic state of La$_{5/8}$Ca$_{3/8}$MnO$_3$. The measurement of
tunable phase separation via magnetic neutron powder diffraction presents a
direct route of exploring the correlated spin properties of phase separated
charge/magnetic order in highly strained CMR materials and opens a potential
avenue for realizing intergrain spin tunnel junction networks with enhanced CMR
behavior in a chemically homogeneous material.

###Data Storage: Review of Heusler Compounds|Zhaoqiang Bai,Lei Shen,Guchang Han,Yuan ping Feng###

Data Storage: Review of Heusler Compounds. In the recent decade, the family of Heusler compounds has attracted
tremendous scientific and technological interest in the field of spintronics.
This is essentially due to their exceptional magnetic properties, which qualify
them as promising functional materials in various data-storage devices, such as
giant-magnetoresistance spin valves, magnetic tunnel junctions, and
spin-transfer torque devices. In this article, we provide a comprehensive
review on the applications of the Heusler family in magnetic data storage. In
addition to their important roles in the performance improvement of these
devices, we also try to point out the challenges as well as possible solutions,
of the current Heusler-based devices. We hope that this review would spark
further investigation efforts into efficient incorporation of this eminent
family of materials into data storage applications by fully arousing their
intrinsic potential.

###Efficient spin injection and giant magnetoresistance in Fe/MoS$_2$/Fe junctions|Kapildeb Dolui,Awadhesh Narayan,Ivan Rungger,Stefano Sanvito###

Efficient spin injection and giant magnetoresistance in Fe/MoS$_2$/Fe junctions. We demonstrate giant magnetoresistance in Fe/MoS$_2$/Fe junctions by means of
\textit{ab-initio} transport calculations. We show that junctions incorporating
either a mono- or a bi-layer of MoS$_2$ are metallic and that Fe acts as an
efficient spin injector into MoS$_2$ with an efficiency of about 45\%. This is
the result of the strong coupling between the Fe and S atoms at the interface.
For junctions of greater thickness a maximum magnetoresistance of $\sim$300\%
is obtained, which remains robust with the applied bias as long as transport is
in the tunneling limit. A general recipe for improving the magnetoresistance in
spin valves incorporating layered transition metal dichalcogenides is proposed.

###Band-pass Magnetic Tunnel Junction based Magnetoresistive Random Access Memory|Abhishek Sharma,Ashwin Tulapurkar,Bhaskaran Muralidharan###

Band-pass Magnetic Tunnel Junction based Magnetoresistive Random Access Memory. We propose spin transfer torque--magnetoresistive random access memory
(STT-MRAM) based on magneto-resistance and spin transfer torque physics of
band-pass spin filtering. Utilizing the electronic analogs of optical phenomena
such as anti-reflection coating and resonance for spintronic devices, we
present the design of an STT-MRAM device with improved features when compared
with a traditional trilayer device. The device consists of a superlattice
heterostructure terminated with the anti-reflective regions sandwiched between
the fixed and free ferromagnetic layers. Employing the Green's function spin
transport formalism coupled self-consistently with the stochastic
Landau-Lifshitz-Gilbert-Slonczewski equation, we present the design of an
STT-MRAM based on the band-pass filtering having an ultra-high TMR (3.5*10e4)
and large spin current. We demonstrate that the STT-MRAM design having
band-pass spin filtering are nearly 1100% more energy efficient than
traditional trilayer magnetic tunnel junction (MTJ) based STT-MRAM. We also
present detailed probabilistic switching and energy analysis for a trilayer MTJ
and band-pass filtering based STT-MRAM. Our predictions serve as a template to
consider the heterostructures for next-generation spintronic device
applications.

###Tunneling anisotropic magnetoresistance and spin-orbit coupling in Fe/GaAs/Au tunnel junctions|J. Moser,A. Matos-Abiague,D. Schuh,W. Wegscheider,J. Fabian,D. Weiss###

Tunneling anisotropic magnetoresistance and spin-orbit coupling in Fe/GaAs/Au tunnel junctions. We report the observation of tunneling anisotropic magnetoresistance effect
(TAMR) in the epitaxial metal-semiconductor system Fe/GaAs/Au. The observed
two-fold anisotropy of the resistance can be switched by reversing the bias
voltage, suggesting that the effect originates from the interference of the
spin-orbit coupling at the interfaces. Corresponding model calculations
reproduce the experimental findings very well.

###Inverse Magnetoresistance of Molecular Junctions|Hugh Dalgleish,George Kirczenow###

Inverse Magnetoresistance of Molecular Junctions. We present calculations of spin-dependent electron transport through single
organic molecules bridging pairs of iron nanocontacts. We predict the
magnetoresistance of these systems to switch from positive to negative with
increasing applied bias for both conducting and insulating molecules. This
novel inverse magnetoresistance phenomenon is robust, does not depend on the
presence of impurities, and is unique to molecular and atomic nanoscale
magnetic junctions. Its physical origin is identified and its relevance to
experiment and to potential technological applications is discussed.

###Double Free-Layer Magnetic Tunnel Junctions for Probabilistic Bits|Kerem Y. Camsari,Mustafa Mert Torunbalci,William A. Borders,Hideo Ohno,Shunsuke Fukami###

Double Free-Layer Magnetic Tunnel Junctions for Probabilistic Bits. Naturally random devices that exploit ambient thermal noise have recently
attracted attention as hardware primitives for accelerating probabilistic
computing applications. One such approach is to use a low barrier nanomagnet as
the free layer of a magnetic tunnel junction (MTJ) whose magnetic fluctuations
are converted to resistance fluctuations in the presence of a stable fixed
layer. Here, we propose and theoretically analyze a magnetic tunnel junction
with no fixed layers but two free layers that are circularly shaped disk
magnets. We use an experimentally benchmarked model that accounts for finite
temperature magnetization dynamics, bias-dependent charge and spin-polarized
currents as well as the dipolar coupling between the free layers. We obtain
analytical results for statistical averages of fluctuations that are in good
agreement with the numerical model. We find that the free layers with low
diameters fluctuate to randomize the resistance of the MTJ in an approximately
bias-independent manner. We show how such MTJs can be used to build a binary
stochastic neuron (or a p-bit) in hardware. Unlike earlier stochastic MTJs that
need to operate at a specific bias point to produce random fluctuations, the
proposed design can be random for a wide range of bias values, independent of
spin-transfer-torque pinning. Moreover, in the absence of a carefully optimized
stabled fixed layer, the symmetric double-free layer stack can be manufactured
using present day Magnetoresistive Random Access Memory (MRAM) technology by
minimal changes to the fabrication process. Such devices can be used as
hardware accelerators in energy-efficient computing schemes that require a
large throughput of tunably random bits.

###Impurities and Inelastic Processes in Magnetic Tunnel Junctions|A. M. Bratkovsky,J. H. Nickel###

Impurities and Inelastic Processes in Magnetic Tunnel Junctions. We have studied tunnel magnetoresistance (TMR) in junctions with 3d
ferromagnetic electrodes. Previously we predicted that defects in the barrier
would result in reduced effective polarization P of the impurity assisted
current. This is confirmed experimentally in the present work: introductions of
defects into the barrier drastically decreases the TMR. The degradation of
magnetoresistance with bias has also been studied and shows universal features,
attributed to effects of tunneling assisted by magnons and phonons, whose
different role is described. Details of the bias dependence of the TMR depend
on preparation procedures and well described by the model which includes
assisted tunneling. Non-linear features, seen at low biases, are related to
excitation of bulk modes by tunneling electrons. The analysis of factors
resulting in fall-off of the TMR with bias is presented.

###Large anomalous unidirectional magnetoresistance in a single ferromagnetic layer|Kaihua Lou,Qianwen Zhao,Baiqing Jiang,Chong Bi###

Large anomalous unidirectional magnetoresistance in a single ferromagnetic layer. Unidirectional magnetoresistance (UMR) in a ferromagnetic bilayer due to the
spin Hall effects (SHEs) provides a facile means of probing in-plane
magnetization to avoid complex magnetic tunnel junctions. However, the UMR
signal is very weak and usually requires a lock-in amplifier for detection even
in the bilayer involving Ta or Pt with a large spin Hall angle (SHA). Here we
report a type of UMR, termed as the anomalous UMR (AUMR), in a single CoFeB
layer without any adjacent SHE layers, where the UMR signal is about 10 times
larger than that in Ta/CoFeB structures and can be detected by using
conventional dc multimeters in the absence of lock-in amplifiers. We further
demonstrate that the extracted AUMR by excluding thermal contributions shows
reversal signs for the CoFeB and NiFe single layers with opposite SHAs,
indicating that the AUMR may originate from the self-generated spin
accumulation interacting with magnetization through the giant
magnetoresistance-like mechanism. These results suggest that the AUMR
contributes UMR signals larger than the interfacial spin Hall UMR in the
CoFeB-involved systems, providing a convenient and reliable approach to detect
in-plane magnetization for the two-terminal spintronic devices.

###Strength of the symmetry spin filtering effect in magnetic tunnel junctions|Sergey V. Faleev,Stuart S. P. Parkin,Oleg N. Mryasov###

Strength of the symmetry spin filtering effect in magnetic tunnel junctions. Strength of the the symmetry spin filtering effect (as defined by the
asymptotic behavior of the tunneling magnetoresistance (TMR) at large barrier
thicknesses induced by this effect) is studied for the Fe/MgO/Fe magnetic
tunnel junctions (MTJ). Based on the analysis of the band structure of bulk Fe
and complex band structure of MgO we predict \emph{native} for the symmetry
spin filtering effect linear increase of the TMR in Fe/MgO/Fe MTJ with
increasing number of MgO layers, $N$. \emph{Ab initio} calculations of
transmission functions performed for the Fe/MgO/Fe MTJ confirm our theoretical
predictions for the strength of the symmetry spin filtering effect in broad
range of energies and $N$. Our calculations also show that the
\emph{combination} of the symmetry spin filtering effect and small surface
transmission function in minority spin channel at the Fe/MgO interface is
responsible for large $TMR>10,000\%$ predicted for Fe/MgO/Fe MTJ for $N
\geqslant 8$. Proposed analysis of the strength of the symmetry filtering
effect derived from the band structure of bulk electrode material could serve
as a tool for quick material discovery search of suitable electrodes in context
of emerging technologies that require high TMR.

###TMR transition and highly sensitive pressure sensors based on magnetic tunnel junctions with black phosphorus barrier|Fang Henan,Li Qian,Xiao Mingwen,Liu Yan###

TMR transition and highly sensitive pressure sensors based on magnetic tunnel junctions with black phosphorus barrier. Black phosphorus is a promising material to serve as the barrier of magnetic
tunnel junctions (MTJs) due to the weak van der Waals interlayer interactions.
In particular, the special band features of black phosphorus may bring
intriguing physical characteristics. Here, we study theoretically the effect of
band gap tunability of black phosphorus on the MTJs with black phosphorus
barrier. It is found that, the tunneling magnetoresistance (TMR) may achieve a
transition from finite value to infinity owing to the variation of the band gap
of black phosphorus. Combining with the latest experimental results of the
pressure-induced band gap tunability, we further investigate the pressure
effect of TMR in the MTJs with black phosphorus barrier. The calculations show
that the pressure sensitivity can be quite high under appropriate parameters.
Physically, the high sensitivity originates from the TMR transition phenomenon.
To take advantage of the high pressure sensitivity, we propose and design a
detailed structure of highly sensitive pressure sensors based on MTJs with
black phosphorus barrier, whose working mechanism is basically different from
the convential pressure sensors. The present pressure sensors possess four
advantages and benifits: (1) high sensitivity, (2) well anti-interference, (3)
high spatial resolution, and (4) fast response speed. Our study may advance new
research area for both the MTJs and pressure sensors.

###Interface-Assisted Room-Temperature Magnetoresistance in Cu-Phenalenyl-based Magnetic Tunnel Junctions|Neha Jha,Anand Paryar,Tahereh Sadat Parvini,Christian Denker,Pavan K. Vardhanapu,Gonela Vijaykumar,Arne Ahrens,Michael Seibt,Jagadeesh S. Moodera,Swadhin K. Mandal,Markus Münzenberg###

Interface-Assisted Room-Temperature Magnetoresistance in Cu-Phenalenyl-based Magnetic Tunnel Junctions. Delocalized carbon-based radical species with unpaired spin, such as
phenalenyl (PLY) radical, opened avenues for developing multifunctional organic
spintronic devices. Here we develop a novel technique based on a
three-dimensional shadow mask and the in-situ deposition to fabricate PLY-,
Cu-PLY-, and Zn-PLY-based organic magnetic tunnel junctions (OMTJs) with area
3x8 {\mu}m2 and improved morphology. The nonlinear and weakly
temperature-dependent current-voltage (I-V) characteristics in combination with
the low organic barrier height suggest tunneling as the dominant transport
mechanism in the structurally and dimensionally optimized OMTJs. Cu-PLY-based
OMTJs, show a significant magnetoresistance up to 14 percent at room
temperature due to the formation of hybrid states at the metal-molecule
interfaces called spinterface, which reveals the importance of spin-dependent
interfacial modification in OMTJs design. In particular, Cu-PLY OMTJs shows a
stable voltage-driven resistive switching response that suggests their use as a
new viable and scalable platform for building molecular scale quantum
memristors and processors.

###Transport across junctions of altermagnets with normal metals and ferromagnets|Sachchidanand Das,Dhavala Suri,Abhiram Soori###

Transport across junctions of altermagnets with normal metals and ferromagnets. Altermagnet (AM) is a novel time reversal symmetry broken magnetic phase with
$d$-wave order. We discuss theoretical models of altermagnet based systems on
lattice and in continuum that are amenable to experimental measurements and
show equivalence between the two models. We study (i) altermagnet-normal metal
(NM) and (ii) altermagnet-ferromagnet (FM) junctions, with the aim to quantify
transport properties such as conductivity and magnetoresistance. We find that a
spin current accompanies charge current when a bias is applied. The
magnetoresistance of the AM-FM junction switches sign when AM is rotated by
$90^{\circ}$, -a feature unique to the altermagnetic phase.

###Nonvolatile SRAM architecture using MOSFET-based spin-transistors|Yusuke Shuto,Shuu'ichirou Yamamoto,Satoshi Sugahara###

Nonvolatile SRAM architecture using MOSFET-based spin-transistors. The authors proposed and computationally analyzed nonvolatile static random
access memory (NV-SRAM) architecture using metal-oxide-semiconductor
field-effect transistor (MOSFET) type of spin-transistors referred to as
pseudo-spin-MOSFET (PS-MOSFET). PS-MOSFET is a new circuit approach to
reproduce the functions of spin-transistors, based on recently progressed
magnetoresistive random access memory (MRAM) technology. The proposed NV-SRAM
cell can be simply configured by connecting two PS-MOSFETs to the storage nodes
of a standard SRAM cell. The logic information of the storage nodes can be
electrically stored into the magnetic tunnel junctions (MTJs) of the PS-MOSFETs
by current-induced magnetization switching (CIMS), and the stored information
is automatically restored when the inverter loop circuit wakes up. In addition,
the proposed NV-SRAM cell has no influence on the performance of normal SRAM
operations. Low power dissipation and high degree of freedom of MTJ design are
also remarkable features for NV-SRAM using PS-MOSFETs.

###Magnetoresistance of an Anderson insulator of bosons|Anirban Gangopadhyay,Victor Galitski,Markus Mueller###

Magnetoresistance of an Anderson insulator of bosons. We study the magnetoresistance of two-dimensional bosonic Anderson
insulators. We describe the change in spatial decay of localized excitations in
response to a magnetic field, which is given by an interference sum over
alternative tunnelling trajectories. The excitations become more localized with
increasing field (in sharp contrast to generic fermionic excitations which get
weakly delocalized): the localization length \xi(B) is found to change as
\xi^{-1}(B)-\xi^{-1}(0)\sim B^{4/5}. The quantum interference problem maps onto
the classical statistical mechanics of directed polymers in random media
(DPRM). We explain the observed scaling using a simplified droplet model which
incorporates the non-trivial DPRM exponents. Our results have implications for
a variety of experiments on magnetic-field-tuned superconductor-to-insulator
transitions observed in disordered films, granular superconductors, and
Josephson junction arrays, as well as for cold atoms in artificial gauge
fields.

###Low frequency non-resonant rectification in spin-diodes|R. Tomasello,B. Fang,P. Artemchuk,M. Carpentieri,L. Fasano,A. Giordano,O. V. Prokopenko,Z. M. Zeng,G. Finocchio7###

Low frequency non-resonant rectification in spin-diodes. Spin-diodes are usually resonant in nature (GHz frequency) and tuneable by
magnetic field and bias current with performances, in terms of sensitivity and
minimum detectable power, overcoming the semiconductor counterpart, i.e.
Schottky diodes. Recently, spin diodes characterized by a low frequency
detection (MHz frequency) have been proposed. Here, we show a strategy to
design low frequency detectors based on magnetic tunnel junctions having the
interfacial perpendicular anisotropy of the same order of the demagnetizing
field out-of-plane component. Micromagnetic calculations show that to reach
this detection regime a threshold input power has to be overcome and the phase
shift between the oscillation magnetoresistive signal and the input
radiofrequency current plays the key role in determining the value of the
rectification voltage.

###Spin-polarized quantum transport properties through flexible phosphorene|Mingyan Chen,Zhizhou Yu,Yiqun Xie,Yin Wang###

Spin-polarized quantum transport properties through flexible phosphorene. We report a first-principles study on the tunnel magnetoresistance (TMR) and
spin-injection efficiency (SIE) through phosphorene with nickel electrodes
under the mechanical tension and bending on the phosphorene region. Both the
TMR and SIE are largely improved under these mechanical deformations. For the
uniaxial tension ($\varepsilon_y$) varying from 0 to 15\% applied along the
armchair transport ({\it y}-)direction of the phosphorene, the TMR ratio is
enhanced with a maximum of 107\% at the $\varepsilon_y=10\%$, while the SIE
increases monotonously from 8\% up to 43\% with the increasing of the strain.
Under the out-of-plane bending, the TMR overall increases from 7\% to 50\%
within the bending ratio of 0-3.9\%, and meanwhile the SIE is largely improved
to around 70\%, as compared to that (30\%) of the flat phosphorene. Such
behaviors of the TMR and SIE are mainly affected by the transmission of spin-up
electrons in the parallel configuration, which is highly depended on the
applied mechanical tension and bending. Our results indicate that the
phosphorene based tunnel junctions have promising applications in flexible
electronics.

###Antiferromagnetic Skyrmion based Energy-Efficient Leaky Integrate and Fire Neuron Device|Namita Bindal,Ravish Kumar Raj,Md Mahadi Rajib,Jayasimha Atulasimha,Brajesh Kumar Kaushik###

Antiferromagnetic Skyrmion based Energy-Efficient Leaky Integrate and Fire Neuron Device. The development of energy-efficient neuromorphic hardware using spintronic
devices based on antiferromagnetic (AFM) skyrmion motion on nanotracks has
gained considerable interest. Owing to its properties such as robustness
against external magnetic fields, negligible stray fields, and zero net
topological charge, AFM skyrmions follow straight trajectories that prevent
their annihilation at nanoscale racetrack edges. This makes the AFM skyrmions a
more favorable candidate over the ferromagnetic (FM) skyrmion for future
spintronic applications. This work proposes an AFM skyrmion-based neuron device
exhibiting the leaky-integrate-fire (LIF) functionality by exploiting thermal
gradient or alternatively perpendicular magnetic anisotropy (PMA) gradient in
the nanotrack for leaky behavior by moving the skyrmion in the direction to
minimize the system energy. Furthermore, it is shown that the AFM skyrmion
couples efficiently to the soft ferromagnetic layer of a magnetic tunnel
junction enabling efficient read-out of the skyrmion. The maximum change of
9.2% in tunnel magnetoresistance (TMR) is estimated for detecting the AFM
skyrmion. Moreover, the proposed neuron device has the energy dissipation of
4.32 fJ per LIF operation thus, paving the path for developing energy-efficient
devices in antiferromagnetic spintronics for neuromorphic computing.

###Spin-relaxation and magnetoresistance in FM/SC/FM tunnel junctions|Saburo Takahashi,Taro Yamashita,Hiroshi Imamura,Sadamichi Maekawa###

Spin-relaxation and magnetoresistance in FM/SC/FM tunnel junctions. The effect of spin relaxation on tunnel magnetoresistance (TMR) in a
ferromagnet/superconductor/ferromagnet (FM/SC/FM) double tunnel junction is
theoretically studied. The spin accumulation in SC is determined by balancing
of the spin-injection rate and the spin-relaxation rate. In the superconducting
state, the spin-relaxation time becomes longer with decreasing temperature,
resulting in a rapid increase of TMR. The TMR of FM/SC/FM junctions provides a
useful probe to extract information about spin-relaxation in superconductors.

###Proximity-induced superconducting gap in the intrinsic magnetic topological insulator MnBi2Te4|Wen-Zheng Xu,Chun-Guang Chu,Zhen-Cun Pan,Jing-Jing Chen,An-Qi Wang,Zhen-Bing Tan,Peng-Fei Zhu,Xing-Guo Ye,Da-Peng Yu,Zhi-Min Liao###

Proximity-induced superconducting gap in the intrinsic magnetic topological insulator MnBi2Te4. We report magnetotransport measurements in the NbN/ magnetic topological
insulator MnBi2Te4 (MBT)/ NbN junction at low temperature. At 10 mK, the
nonlinear current-voltage characteristic of the junction shows a tunneling
behavior, indicating the existence of interfacial potential barriers within the
heterostructure. Under an out of plane perpendicular magnetic field, a
transition from negative to positive magnetoresistance (MR) is found when
increasing the bias voltage. A proximity-induced superconducting gap is
estimated to be 0.1meV by a pair of differential resistance dips. Moreover, the
induced gap is enhanced by gradually tuning the Fermi level toward the charge
neutral point by a back gate voltage, which is ascribed to the increased
transport contribution of the topological surface states in MBT. Intriguingly,
the induced gap exhibits an anomalous magnetic field assisted enhancement,
which may originate from the spin orbit coupling and magnetic order of MBT. Our
results reveal the interplay between magnetism and superconductivity in MBT,
paving the way for further studies on topological superconductivity and chiral
Majorana edge modes in quantum anomalous Hall insulator/superconductor hybrid
systems.

###Collective Josephson vortex dynamics in a finite number of intrinsic Josephson junctions|Myung-Ho Bae,Jae-Hyun Choi,Hu-Jong Lee###

Collective Josephson vortex dynamics in a finite number of intrinsic Josephson junctions. We report the experimental confirmation of the collective transverse plasma
modes excited by the Josephson vortex lattice in stacks of intrinsic Josephson
junctions in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ single crystals. The
excitation was confirmed by analyzing the temperature ($T$) and magnetic field
($H$) dependencies of the multiple sub-branches in the Josephson-vortex-flow
region of the current-voltage characteristics of the system. In the near-static
Josephson vortex state for a low tunneling bias current, pronounced
magnetoresistance oscillations were observed, which represented a
triangular-lattice vortex configuration along the c axis. In the dynamic vortex
state in a sufficiently high magnetic field and for a high bias current,
splitting of a single Josephson vortex-flow branch into multiple sub-branches
was observed. Detailed examination of the sub-branches for varying $H$ field
reveals that sub-branches represent the different modes of the Josephson-vortex
lattice along the c axis, with varied configuration from a triangular to a
rectangular lattices. These multiple sub-branches merge to a single curve at a
characteristic temperature, above which no dynamical structural transitions of
the Josephson vortex lattice is expected.

###Asymmetric $d$-wave superconducting topological insulator in proximity with a magnetic order|M. Khezerlou,H. Goudarzi###

Asymmetric $d$-wave superconducting topological insulator in proximity with a magnetic order. In the framework of the Dirac-Bogoliubov-de Gennes formalism, we investigate
the transport properties in the surface of a 3-dimensional topological
insulator-based hybrid structure, where the ferromagnetic and superconducting
orders are simultaneously induced to the surface states via the proximity
effect. The superconductor gap is taken to be spin-singlet $d$-wave symmetry.
The asymmetric role of this gap respect to the electron-hole exchange, in one
hand, affects the topological insulator superconducting binding excitations
and, on the other hand, gives rise to forming distinct Majorana bound states at
the ferromagnet/superconductor interface. We propose a topological insulator
N/F/FS junction and proceed to clarify the role of $d$-wave asymmetry pairing
in the resulting subgap and overgap tunneling conductance. The perpendicular
component of magnetizations in F and FS regions can be at the parallel and
antiparallel configurations leading to capture the experimentally important
magnetoresistance (MR) of junction. It is found that the zero-bias conductance
is strongly sensitive to the magnitude of magnetization in FS region $m_{zfs}$
and orbital rotated angle $\alpha$ of superconductor gap. The negative MR only
occurs in zero orbital rotated angle. This result can pave the way to
distinguish the unconventional superconducting state in the relating
topological insulator hybrid structures.

###Anomalous bias dependence of tunnel magnetoresistance in a magnetic tunnel junction|Soumik Mukhopadhyay,I. Das,S. P. Pai,P. Raychaudhuri###

Anomalous bias dependence of tunnel magnetoresistance in a magnetic tunnel junction. We have fabricated a spin-polarized tunneling device based on half metallic
manganites incorporating $Ba_{2}LaNbO_{6}$ as insulating barrier. An anomalous
bias dependence of tunnel magnetoresistance (TMR) has been observed, the first
of its kind in a symmetric electrode tunnel junction with single insulating
barrier. The bias dependence of TMR shows an extremely sharp zero bias anomaly,
which can be considered as a demonstration of the drastic density of states
variation around the Fermi level of the half metal. This serves as a strong
evidence for the existence of minority spin tunneling states at the half-metal
insulator interface.

###Spin-polarized transport in inhomogeneous magnetic semiconductors: theory of magnetic/nonmagnetic p-n junctions|Igor Zutic,Jaroslav Fabian,S. Das Sarma###

Spin-polarized transport in inhomogeneous magnetic semiconductors: theory of magnetic/nonmagnetic p-n junctions. A theory of spin-polarized transport in inhomogeneous magnetic semiconductors
is developed and applied to magnetic/nonmagnetic p-n junctions. Several
phenomena with possible spintronic applications are predicted, including
spinvoltaic effect, spin valve effect, and giant magnetoresistance. It is
demonstrated that only nonequilibrium spin can be injected across the
space-charge region of a p-n junction, so that there is no spin injection (or
extraction) at low bias.

###All-electrical measurement of spin injection in a magnetic $p$-$n$ junction diode|Peifeng Chen,Juergen Moser,Philipp Kotissek,Janusz Sadowski,Marcus Zenger,Dieter Weiss,Werner Wegscheider###

All-electrical measurement of spin injection in a magnetic $p$-$n$ junction diode. Magnetic $p$-$n$ junction diodes are fabricated to investigate spin-polarized
electron transport. The injection of spin-polarized electrons in a
semiconductor is achieved by driving a current from a ferromagnetic injector
(Fe), into a bulk semiconductor ($n$-GaAs) via schottky contact. For detection,
a diluted magnetic semiconductor ($p$-GaMnAs) layer is used. Clear
magnetoresistance was observed only when a high forward bias was applied across
the $p$-$n$ junction.

###Spin Pumping and Inverse Spin Hall Effect in Germanium|J. -C. Rojas-Sánchez,M. Cubukcu,A. Jain,C. Vergnaud,C. Portemont,C. Ducruet,A. Barski,A. Marty,L. Vila,J. -P. Attané,E. Augendre,G. Desfonds,S. Gambarelli,H. Jaffrès,J. -M. George,M. Jamet###

Spin Pumping and Inverse Spin Hall Effect in Germanium. We have measured the inverse spin Hall effect (ISHE) in \textit{n}-Ge at room
temperature. The spin current in germanium was generated by spin pumping from a
CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch
issue. A clear electromotive force was measured in Ge at the ferromagnetic
resonance of CoFeB. The same study was then carried out on several test
samples, in particular we have investigated the influence of the MgO tunnel
barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO
bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to
anisotropic magnetoresistance and anomalous Hall effect which is dominated by
an asymmetric contribution with respect to the resonance field. We also found
that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample
annealing systematically lead to an increase of the signal. We propose a
theoretical model based on the presence of localized states at the interface
between the MgO tunnel barrier and Ge to account for these observations.
Finally, all of our results are fully consistent with the observation of ISHE
in heavily doped $n$-Ge and we could estimate the spin Hall angle at room
temperature to be $\approx$0.001.

###Tunnel magnetoresistance of a supramolecular spin valve|A. Plominska,I. Weymann###

Tunnel magnetoresistance of a supramolecular spin valve. We theoretically study the transport properties of a supramolecular spin
valve, consisting of a carbon nanotube with two attached magnetic molecules,
weakly coupled to metallic contacts. The emphasis is put on analyzing the
change of the system's transport properties with the application of an external
magnetic field, which aligns the spins of the molecules. It is shown that
magnetoresistive properties of the considered molecular junction, which are
associated with changing the state of the molecules from superparamagnetic to
the ferromagnetic one, strongly depend on the applied bias voltage and the
position of the nanotube's orbital levels, which can be tuned by a gate
voltage. A strong dependence on the transport regime is also found in the case
of the spin polarization of the current flowing through the system. The
mechanisms leading to those effects are explained by invoking appropriate
molecular states responsible for transport. The analysis is done with aid of
the real-time diagrammatic technique up to the second order of expansion with
respect to tunneling processes.

###Temperature- and Bias-dependence of magnetoresistance in doped manganite thin film trilayer junctions|J. Z. Sun,D. W. Abraham,K. Roche,S. S. P. Parkin###

Temperature- and Bias-dependence of magnetoresistance in doped manganite thin film trilayer junctions. Thin film trilayer junction of La$%_{0.67}$Sr$_{0.33}$MnO$_3$ - SrTiO$_3$ -
La$_{0.67}$Sr$_{0.33}$MnO$_3$ shows a factor of 9.7 change in resistance, in a
magnetic field around 100 Oe at 14K. The junction magnetoresistance is bias and
temperature dependent. The energy scales associated with bias and temperature
dependence are an order of magnitude apart. The same set of energies also
determine the bias and temperature dependence of the differential conductance
of the junction. We discuss these results in terms of metallic cluster
inclusions at the junction-barrier interface.

###Giant magnetoresistance in antiferromagnetic Mn$_2$Au-based tunnel junction|Xing-Tao Jia,Xiao-Lin Cai,Yu Jia###

Giant magnetoresistance in antiferromagnetic Mn$_2$Au-based tunnel junction. Recent studies on the electrical switching of tetragonal antiferromagnet
(AFM) via N{\'e}el spin-orbit torque have paved the way for the economic use of
antiferromagnetic materials. The most difficult obstacle that presently limits
the application of antiferromagnetic materials in spintronics, especially in
memory storage applications, could be the small and fragile magnetoresistance
(MR) in the AFM-based nanostructure. In this study, we investigated the spin
transports in Mn$_2$Au-based tunnel junctions based onthe first-principle
scattering theory. Giant MRs more than $1000\%$ are predicted in some
Fe/MgO/Ag/Mn$_2$Au/Ta junctions that are about the same order as that in an
MgO-based ferromagnetic tunnel junction with same barrier thickness. The
interplay of the spin filtering effect, the quantum well resonant states, and
the interfacial resonant states could be responsible for the unusual giant and
robust MRs observed in these Mn$_2$Au-based junctions.

###Anisotropy and Current Control of Magnetization in SrRuO$_3$ SrTiO$_3$ Heterostructures for Spin-Memristors|A. S. Goossens,M. A. T. Leiviskä,T. Banerjee###

Anisotropy and Current Control of Magnetization in SrRuO$_3$ SrTiO$_3$ Heterostructures for Spin-Memristors. Spintronics-based nonvolatile components in neuromorphic circuits offer the
possibility of realizing novel functionalities at low power. Current-controlled
electrical switching of magnetization is actively researched in this context.
Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA),
consisting of SrRuO$_3$ (SRO) grown on SrTiO$_3$ (STO) are strong material
contenders. Utilizing the crystal orientation, magnetic anisotropy in such
simple heterostructures can be tuned to either exhibit a perfect or slightly
tilted PMA. Here, we investigate current-induced magnetization modulation in
such tailored ferromagnetic layers with a material with strong spin-orbit
coupling (Pt), exploiting the spin Hall effect. We find significant differences
in the magnetic anisotropy between the SRO/STO heterostructures, as manifested
in the first and second harmonic magnetoresistance measurements.
Current-induced magnetization switching can be realized with spin-orbit
torques, but for systems with perfect PMA this switching is probabilistic as a
result of the high symmetry. Slight tilting of the PMA can break this symmetry
and allow the realization of deterministic switching. Control over the magnetic
anisotropy of our heterostructures therefore provides control over the manner
of switching. Based on our findings, we propose a three-terminal spintronic
memristor, with a magnetic tunnel junction design, that shows several resistive
states controlled by electric charge. Non-volatile states can be written
through SOT by applying an in-plane current, and read out as a tunnel current
by applying a small out-of-plane current. Depending on the anisotropy of the
SRO layer, the writing mechanism is either deterministic or probabilistic
allowing for different functionalities to emerge. We envisage that the
probabilistic MTJs could be used as synapses while the deterministic devices
can emulate neurons

###Gap like structure in a nonsuperconducting layered oxycarbonate Bi$_{2+x}$Sr$_{4-x}$Cu$_2$CO$_3$O$_{8+δ}$ single crystal|S. I. Vedeneev,B. A. Piot,D. K. Maude###

Gap like structure in a nonsuperconducting layered oxycarbonate Bi$_{2+x}$Sr$_{4-x}$Cu$_2$CO$_3$O$_{8+δ}$ single crystal. The magnetic field and temperature dependence of the in-plane tunneling
conductance $dI/dV(V)$ in high-quality nonsuperconducting (down to 10 mK)
layered oxycarbonate Bi$_{2+x}$Sr$_{4-x}$Cu$_2$CO$_3$O$_{8+\delta}$ single
crystals has been investigated using break junctions. Combining measurements of
the in-plane magnetoresistivity $\rho_{ab}(T,H)$ and the magnetotunneling, we
present evidence for the existence of a small "pseudogap" in a
nonsuperconducting cuprate, without local incoherent pairs or any correlation
phenomena associated with superconductivity. We are unable to distinguish if
such a "pseudogap" is totally unrelated to superconductivity or if its
existence is a necessary condition for the subsequent occurrence of
superconductivity with increasing carrier density in the sample.

###Low-Frequency Microwave Induced Quantum Oscillations in A Two-Dimensional Electron System|Jian Mi,Huiying Liu,Junren Shi,L. N. Pfeiffer,K. W. West,K. W. Baldwin,Chi Zhang###

Low-Frequency Microwave Induced Quantum Oscillations in A Two-Dimensional Electron System. We study the magnetoresistance of an ultrahigh mobility GaAs/AlGaAs
two-dimensional electron sample in a weak magnetic field under low-frequency (f
< 20 GHz) microwave (MW) irradiation. We observe that with decreasing MW
frequency, microwave induced resistance oscillations (MIRO) damp and
multi-photon processes become dominant. At very low MW frequency (f < 4 GHz),
MIRO disappears gradually and a new SdH-like oscillation develops. The analysis
indicates that the new oscillation may originate from alternating Hall-field
induced resistance oscillations (ac-HIRO), or can be viewed as a multi-photon
process of MIRO in low MW frequency limit. Our findings bridge the
non-equilibrium states of MIRO and HIRO, which can be brought into a frame of
quantum tunneling junction model.

###Electronic transport in ferromagnetic barriers on the surface of a topological insulator with $δ$ doping|Jian-Hui Yuan,Yan Zhang,Daizheng Huang,Qinhu Zhong,Xin Zhang###

Electronic transport in ferromagnetic barriers on the surface of a topological insulator with $δ$ doping. We investigate electron transporting through a two-dimensional
ferromagnetic/normal/ferromagnetic tunnel junction on the surface of a
three-dimensional topological insulator with taking into $\delta$ doping
account. It is found that the conductance oscillates with the Fermi energy, the
position and the aptitude of the $\delta$ doping. Also the conductance depends
sensitively on the direction of the magnetization of the two ferromagnets,
which originate from the control of the spin flow due to spin-momentum locked.
It is found that the conductance is the maximum at the parallel configuration
while it is minimum at the antiparallel configuration and vice versa, which may
stem from the half wave loss due to the electron wave entering through the
antiparallel configuration. These characters are very helpful for making new
types of magnetoresistance devices due to the practical applications.

###Electrically-Tunable Stochasticity for Spin-based Neuromorphic Circuits: Self-Adjusting to Variation|Hossein Pourmeidani,Punyashloka Debashis,Zhihong Chen,Ronald F. DeMara,Ramtin Zand###

Electrically-Tunable Stochasticity for Spin-based Neuromorphic Circuits: Self-Adjusting to Variation. Energy-efficient methods are addressed for leveraging low energy barrier
nanomagnetic devices within neuromorphic architectures. Using a
Magnetoresistive Random Access Memory (MRAM) probabilistic device (p-bit) as
the basis of neuronal structures in Deep Belief Networks (DBNs), the impact of
reducing the Magnetic Tunnel Junction's (MTJ's) energy barrier is assessed and
optimized for the resulting stochasticity present in the learning system. This
can mitigate the process variation sensitivity of stochastic DBNs which
encounter a sharp drop-off when energy barriers exceed near-zero kT. As
evaluated for the MNIST dataset for energy barriers at near-zero kT to 2.0 kT
in increments of 0.5 kT, it is shown that the stability factor changes by 5
orders of magnitude. The self-compensating circuit developed herein provides a
compact, and low complexity approach to mitigating process variation impacts
towards practical implementation and fabrication.

###Electric-Field-Controlled Antiferromagnetic Spintronic Devices|Han Yan,Zexin Feng,Peixin Qin,Xiaorong Zhou,Huixin Guo,Xiaoning Wang,Hongyu Chen,Xin Zhang,Haojiang Wu,Chengbao Jiang,Zhiqi Liu###

Electric-Field-Controlled Antiferromagnetic Spintronic Devices. In recent years, the field of antiferromagnetic spintronics has been
substantially advanced. Electric-field control is a promising approach to
achieving ultra-low power spintronic devices via suppressing Joule heating. In
this article, cutting-edge research, including electric-field modulation of
antiferromagnetic spintronic devices using strain, ionic liquids, dielectric
materials, and electrochemical ionic migration, are comprehensively reviewed.
Various emergent topics such as the Neel spin-orbit torque, chiral spintronics,
topological antiferromagnetic spintronics, anisotropic magnetoresistance,
memory devices, two-dimensional magnetism, and magneto-ionic modulation with
respect to antiferromagnets are examined. In conclusion, we envision the
possibility of realizing high-quality room-temperature antiferromagnetic tunnel
junctions, antiferromagnetic spin logic devices, and artificial
antiferromagnetic neurons. It is expected that this work provides an
appropriate and forward-looking perspective that will promote the rapid
development of this field.

###Current-induced switching in single ferromagnetic layer nanopillar junctions|Barbaros Oezyilmaz,Andrew D. Kent###

Current-induced switching in single ferromagnetic layer nanopillar junctions. Current induced magnetization dynamics in asymmetric Cu/Co/Cu single magnetic
layer nanopillars has been studied experimentally at room temperature and in
low magnetic fields applied perpendicular to the thin film plane. In sub-100 nm
junctions produced using a nanostencil process a bistable state with two
distinct resistance values is observed. Current sweeps at fixed applied fields
reveal hysteretic and abrupt transitions between these two resistance states.
The current induced resistance change is 0.5%, a factor of 5 greater than the
anisotropic magnetoresistance (AMR) effect. We present an experimentally
obtained low field phase diagram of current induced magnetization dynamics in
single ferromagnetic layer pillar junctions.

###Tunnelling anisotropic magnetoresistance of Fe/GaAs/Ag(001) junctions from first principles: Effect of hybridized interface resonances|Rudolf Sykora,Ilja Turek###

Tunnelling anisotropic magnetoresistance of Fe/GaAs/Ag(001) junctions from first principles: Effect of hybridized interface resonances. Results of first-principles calculations of the Fe/GaAs/Ag(001) epitaxial
tunnel junctions reveal that hybridization of interface resonances formed at
both interfaces can enhance the tunnelling anisotropic magnetoresistance (TAMR)
of the systems. This mechanism is manifested by a non-monotonic dependence of
the TAMR effect on the thickness of the tunnel barrier, with a maximum for
intermediate thicknesses. A detailed scan of k-resolved transmissions over the
two-dimensional Brillouin zone proves an interplay between a few
hybridization-induced hot spots and a contribution to the tunnelling from the
vicinity of the Gamma-bar point. This interpretation is supported by calculated
properties of a simple tight-binding model of the junction which reproduce
qualitatively most of the features of the first-principles theory.

###Tunnel magnetoresistance of polymeric chains|Kamil Walczak###

Tunnel magnetoresistance of polymeric chains. Coherent spin-dependent electronic transport is investigated in a molecular
junction made of polymeric chain attached to ferromagnetic electrodes (Ni and
Co, respectively). Molecular system is described by a simple Huckel model,
while the coupling to the electrodes is treated through the use of a broad-band
theory. The current flowing through the device is calculated within
non-equilibrium Green's function approach. It is shown that tunnel
magnetoresistance of molecular junction can be quite large (over 100 %)and
strongly depends on: (i) the lenght of the polymeric chain and (ii) the
strength of the molecule-to-electrodes coupling.

###Tunnel Magnetoresistance of a Single-Molecule Junction|Alireza Saffarzadeh###

Tunnel Magnetoresistance of a Single-Molecule Junction. Based on the non-equilibrium Green's function (NEGF) technique and the
Landauer-B\"{u}ttiker theory, the possibility of a molecular spin-electronic
device, which consists of a single C$_{60}$ molecule attached to two
ferromagnetic electrodes with finite cross sections, is investigated. By
studying the coherent spin-dependent transport through the energy levels of the
molecule, it is shown that the tunnel magnetoresistance (TMR) of the molecular
junction depends on the applied voltages and the number of contact points
between the device electrodes and the molecule. The TMR values more than 60%
are obtained by adjusting the related parameters.

###The role of magnetic anisotropy in spin filter junctions|R. V. Chopdekar,B. B. Nelson-Cheeseman,M. Liberati,E. Arenholz,Y. Suzuki###

The role of magnetic anisotropy in spin filter junctions. We have fabricated oxide based spin filter junctions in which we demonstrate
that magnetic anisotropy can be used to tune the transport behavior of spin
filter junctions. Until recently, spin filters have been largely comprised of
polycrystalline materials where the spin filter barrier layer and one of the
electrodes are ferromagnetic. These spin filter junctions have relied on the
weak magnetic coupling between one ferromagnetic electrode and a barrier layer
or the insertion of a nonmagnetic insulating layer in between the spin filter
barrier and electrode. We have demonstrated spin filtering behavior in
La0.7Sr0.3MnO3/chromite/Fe3O4 junctions without nonmagnetic spacer layers where
the interface anisotropy plays a significant role in determining transport
behavior. Detailed studies of chemical and magnetic structure at the interfaces
indicate that abrupt changes in magnetic anisotropy across the
non-isostructural interface is the cause of the significant suppression of
junction magnetoresistance in junctions with MnCr2O4 barrier layers.

###Conductance fingerprints of non-collinear magnetic states in single atom contacts: a first-principles Wannier functions study|Björn Hardrat,Frank Freimuth,Stefan Heinze,Yuriy Mokrousov###

Conductance fingerprints of non-collinear magnetic states in single atom contacts: a first-principles Wannier functions study. We present a first-principles computational scheme for investigating the
ballistic transport properties of one-dimensional nanostructures with
non-collinear magnetic order. The electronic structure is obtained within
density functional theory as implemented in the full-potential linearized
augmented plane-wave (FLAPW) method and mapped to a tight-binding like
transport Hamiltonian via non-collinear Wannier functions. The conductance is
then computed based on the Landauer formula using the Green's function method.
As a first application we study the conductance between two ferromagnetic Co
monowires terminated by single Mn apex atoms as a function of Mn-Mn separation.
We vary the Mn-Mn separation from the contact (about 2.5 to 5 {\AA}) to the far
tunneling regime (5 to 10 {\AA}). The magnetization direction of the Co
electrodes is chosen either in parallel or antiparallel alignment and we allow
for different spin configurations of the two Mn spins. In the tunneling and
into the contact regime the conductance is dominated by $s$-$d_{z^2}$-states.
In the close contact regime (below 3.5 {\AA}) there is an additional
contribution for a parallel magnetization alignment from the $d_{xz}$- and
$d_{yz}$-states which give rise to an increase of the magnetoresistance as it
is absent for antiparallel magnetization. If we allow the Mn spins to relax a
non-collinear spin state is formed close to contact. We demonstrate that the
transition from a collinear to such a non-collinear spin structure as the two
Mn atoms approach leaves a characteristic fingerprint in the distance-dependent
conductance and magnetoresistance of the junction. We explain the effect of the
non-collinear spin state on the conductance based on the spin-dependent
hybridization between the $d_{xz,yz}$-states of the Mn spins and their coupling
to the Co electrodes.

###Magnetic anisotropy in strained manganite films and bicrystal junctions|G. A. Ovsyannikov,V. V. Demidov,A. M. Petrzhik,I. V. Borisenko,A. V. Shadrin,R. Gunnarsson###

Magnetic anisotropy in strained manganite films and bicrystal junctions. Transport and magnetic properties of LSMO manganite thin films and bicrystal
junctions were investigated. Manganite films were epitaxially grown on STO,
LAO, NGO and LSAT substrates and their magnetic anisotropy were determined by
two techniques of magnetic resonance spectroscopy. Compare with cubic
substrates a small (about 0.3 persentage), the anisotropy of the orthorhombic
NGO substrate leads to a uniaxial anisotropy of the magnetic properties of the
films in the plane of the substrate. Samples with different tilt of
crystallographic basal planes of manganite as well as bicrystal junctions with
rotation of the crystallographic axes (RB - junction) and with tilting of basal
planes (TB - junction) were investigated. It was found that on vicinal NGO
substrates the value of magnetic anisotropy could be varied by changing the
substrate inclination angle from 0 to 25 degrees. Measurement of magnetic
anisotropy of manganite bicrystal junction demonstrated the presence of two
ferromagnetically ordered spin subsystems for both types of bicrystal
boundaries RB and TB. The magnitude of the magnetoresistance for TB - junctions
increased with decreasing temperature and with the misorientation angle even
misorientation of easy axes in the parts of junction does not change. Analysis
of the voltage dependencies of bicrystal junction conductivity show that the
low value of the magnetoresistance for the LSMO bicrystal junctions can be
caused by two scattering mechanisms with the spin- flip of spin - polarized
carriers due to the strong electron - electron interactions in a disordered
layer at the bicrystal boundary at low temperatures and the spin-flip by anti
ferromagnetic magnons at high temperatures.

###Interface resistance in ferromagnet/superconductor junctions|A. A. Golubov###

Interface resistance in ferromagnet/superconductor junctions. Results of theoretical study of spin-polarized tunneling in
ferromagnet/superconductor junctions are presented. Spin and charge currents
are calculated as a function of applied voltage and spin polarization in a
ferromagnet. The model takes into account the splitting of different spin
subbands in a ferromagnet and impurity scattering in the contact. The excess
resistance of an FS contact due to the charge-imbalance in a superconductor is
calculated for the first time. The results have implications for spin-coupled
magnetoresistance in ferromagnet/superconductor contacts and for measuring spin
polarization in ferromagnets.

###Giant Magnetoresistance in an all-oxide spacerless junction|Mangala Prasad Singh,Baptiste Carvello,Laurent Ranno###

Giant Magnetoresistance in an all-oxide spacerless junction. We report the fabrication of an oxide-specific type of magnetoresistive
junction, which is a ferromagnetic bilayer. Both electrodes are high
spin-polarization oxides: magnetite (Fe3O4) and manganite (La0.7Sr0.3MnO3).
Negligible magnetic coupling between both ferromagnetic electrodes is realised,
which allows to obtain parallel and antiparallel magnetic configurations of the
electrodes when sweeping the applied magnetic field. The structure exhibits
negative giant magnetoresistance (GMR) at low temperatures. This negative MR
shows that both electrodes stay spin-polarized at the interface and have
opposite spin polarizations, i.e. the Fe3O4 layer has a negative spin
polarization at low temperature. Maximum GMR (-5%) is obtained at 55K.

###Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions|X. -G. Zhang,W. H. Butler###

Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions. By use of first-principles electronic structure calculations, we predict that
the magnetoresistance of the bcc Co(100)/MgO(100)/bcc Co(100) and
FeCo(100)/MgO(100)/FeCo(100) tunneling junctions can be several times larger
than the very large magnetoresistance predicted for the
Fe(100)/MgO(100)/Fe(100) system. The origin of this large magnetoresistance can
be understood using simple physical arguments by considering the electrons at
the Fermi energy travelling perpendicular to the interfaces. For the minority
spins there is no state with $\Delta_1$ symmetry whereas for the majority spins
there is only a $\Delta_1$ state. The $\Delta_1$ state decays much more slowly
than the other states within the MgO barrier. In the absence of scattering
which breaks the conservation of momentum parallel to the interfaces, the
electrons travelling perpendicular to the interfaces undergo total reflection
if the moments of the electrodes are anti-parallel. These arguments apply
equally well to systems with other well ordered tunnel barriers and for which
the most slowly decaying complex energy band in the barrier has $\Delta_1$
symmetry. Examples include systems with (100) layers constructed from Fe, bcc
Co, or bcc FeCo electrodes and Ge, GaAs, or ZnSe barriers.

###Giant magnetoresistance in the junction of two ferromagnets on the surface of diffusive topological insulators|Katsuhisa Taguchi,Takehito Yokoyama,Yukio Tanaka###

Giant magnetoresistance in the junction of two ferromagnets on the surface of diffusive topological insulators. We reveal the giant magnetoresistance induced by the spin-polarized current
in the ferromagnet (F_1)/topological insulator (TI)/ferromagnet (F_2) junction,
where two ferromagnets are deposited on the diffusive surface of the TI. We can
increase and reduce the value of the giant magnetoresistance by tuning the
spin-polarized current, which is controlled by the magnetization
configurations. The property is intuitively understood by the non-equilibrium
spin-polarized current, which plays the role of an effective electrochemical
potential on the surface of the TI.

###Giant electroresistance and tunable magnetoelectricity in a multiferroic junction|Francesco Ricci,Alessio Filippetti,Vincenzo Fiorentini###

Giant electroresistance and tunable magnetoelectricity in a multiferroic junction. First-principles density functional calculations show that the
$\textrm{SrRuO}_{3}/\textrm{PbTiO}_{3}/\textrm{SrRuO}_{3}$ multiferroic
junction with asymmetric (RuO$_{2}$/PbO and TiO$_{2}$/SrO) interfaces has a
large ferroelectric depolarizing field, whose switching changes the interface
transmission probabilities for tunneling electrons, leading to
electroresistance modulation over several orders of magnitude. The switching
further affects the interface spin density, naturally driving magnetoresistance
as well as modulated spin-dependent in-plane resistivity, which may be
exploited in field-effect devices.

###Tunneling Anisotropic Magnetoresistance in Ferroelectric Tunnel Junctions|A. Alexandrov,M. Ye. Zhuravlev,Evgeny Y. Tsymbal###

Tunneling Anisotropic Magnetoresistance in Ferroelectric Tunnel Junctions. Using a simple quantum-mechanical model, we explore a tunneling anisotropic
magnetoresistance (TAMR) effect in ferroelectric tunnel junctions (FTJs) with a
ferromagnetic electrode and a ferroelectric barrier layer, which spontaneous
polarization gives rise to the Rashba and Dresselhaus spin-orbit coupling
(SOC). For realistic parameters of the model, we predict sizable TAMR
measurable experimentally. For asymmetric FTJs, which electrodes have different
work functions, the built-in electric field affects the SOC parameters and
leads to TAMR dependent on ferroelectric polarization direction. The SOC change
with polarization switching affects tunneling conductance, revealing a new
mechanism of tunneling electroresistance (TER). These results demonstrate new
functionalities of FTJs which can be explored experimentally and used in
electronic devices.

###Ferromagnetic Superconductivity in Two-dimensional Niobium Diselenide|Tingyu Qu,Shangjian Jin,Fuchen Hou,Deyi Fu,Junye Huang,Darryl Foo Chuan Wei,Xiao Chang,Kenji Watanabe,Takashi Taniguchi,Junhao Lin,Shaffique Adam,Barbaros Özyilmaz###

Ferromagnetic Superconductivity in Two-dimensional Niobium Diselenide. The co-existence of ferromagnetism and superconductivity becomes possible
through unconventional pairing in the superconducting state. Such materials are
exceedingly rare in solid-state systems but are promising platforms to explore
topological phases, such as Majorana bound states. Theoretical investigations
date back to the late 1950s, but only a few systems have so far been
experimentally identified as potential hosts. Here, we show that
atomically-thin niobium diselenide (NbSe$_2$) intercalated with dilute cobalt
atoms spontaneously displays ferromagnetism below the superconducting
transition temperature ($T_c$). We elucidate the origin of this phase by
constructing a magnetic tunnel junction that consists of cobalt and
cobalt-doped niobium diselenide (Co-NbSe$_2$) as the two ferromagnetic
electrodes, with an ultra-thin boron nitride as the tunnelling barrier. At a
temperature well below $T_c$, the tunnelling magnetoresistance shows a bistable
state, suggesting a ferromagnetic order in Co-NbSe$_2$. We propose a RKKY
exchange coupling mechanism based on the spin-triplet superconducting order
parameter to mediate such ferromagnetism. We further perform non-local lateral
spin valve measurements to confirm the origin of the ferromagnetism. The
observation of Hanle precession signals show spin diffusion length up to
micrometres below Tc, demonstrating an intrinsic spin-triplet nature in
superconducting NbSe$_2$. Our discovery of superconductivity-mediated
ferromagnetism opens the door to an alternative design of ferromagnetic
superconductors

###Exchange coupling in synthetic anion-engineered chromia heterostructures|Shan Lin,Zhiwen Wang,Qinghua Zhang,Shengru Chen,Qiao Jin,Hongbao Yao,Shuai Xu,Fanqi Meng,Xinmao Yin,Can Wang,Chen Ge,Haizhong Guo,Chi Sin Tang,Andrew T. S. Wee,Lin Gu,Kui-juan Jin,Hongxin Yang,Er-Jia Guo###

Exchange coupling in synthetic anion-engineered chromia heterostructures. Control of magnetic states by external factors has garnered a mainstream
status in spintronic research for designing low power consumption and
fast-response information storage and processing devices. Previously,
magnetic-cation substitution is the conventional means to induce ferromagnetism
in an intrinsic antiferromagnet. Theoretically, the anion-doping is proposed to
be another effect means to change magnetic ground states. Here we demonstrate
the synthesis of high-quality single-phase chromium oxynitride thin films using
in-situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide
and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and
insulating state, as demonstrated by the combination of multiple magnetization
probes and theoretical calculations. With increasing the nitrogen content, the
crystal structure of chromium oxynitride transits from trigonal (R3c) to
tetragonal (4mm) phase and its saturation magnetization reduces significantly.
Furthermore, we achieve a large and controllable exchange bias field in the
chromia heterostructures by synthetic anion engineering. This work reflects the
anion engineering in functional oxides towards the potential applications in
giant magnetoresistance and tunnelling junctions of modern magnetic sensors and
read heads.

###Diagnosis and Location of Pinhole Defects in Tunnel Junctions using only Electrical Measurements|Zhongsheng Zhang,David A. Rabson###

Diagnosis and Location of Pinhole Defects in Tunnel Junctions using only Electrical Measurements. In the development of the first generation of sensors and memory chips based
on spin-dependent tunneling through a thin trilayer, it has become clear that
pinhole defects can have a deleterious effect on magnetoresistance. However,
current diagnostic protocols based on Andreev reflection and the temperature
dependence of junction resistance may not be suitable for production quality
control. We show that the current density in a tunnel junction in the
cross-strip geometry becomes very inhomogeneous in the presence of a single
pinhole, yielding a four-terminal resistance that depends on the location of
the pinhole in the junction. Taking advantage of this position dependence, we
propose a simple protocol of four four-terminal measurements. Solving an
inverse problem, we can diagnose the presence of a pinhole and estimate its
position and resistance.

###YBa2Cu3O7/LaXMnO3 (X: Ca, Sr) based Superconductor/Ferromagnet/Superconductor junctions with memory functionality|R. de Andres Prada,T. Golod,O. M. Kapran,E. A. Borodianskyi,Ch. Bernhard,V. M. Krasnov###

YBa2Cu3O7/LaXMnO3 (X: Ca, Sr) based Superconductor/Ferromagnet/Superconductor junctions with memory functionality. Complex oxides exhibit a variety of unusual physical properties, which can be
used for designing novel electronic devices. Here we fabricate and study
experimentally nano-scale Superconductor/ Ferromagnet/Superconductor junctions
with the high-Tc cuprate superconductor YBa2Cu3O7 and the colossal
magnetoresistive (CMR) manganite ferromagnets LaXMnO3 (X: Ca or Sr). We
demonstrate that in a broad temperature range the magnetization of a manganite
nanoparticle, forming the junction interface, switches abruptly in a
mono-domain manner. The CMR phenomenon translates the magnetization loop into a
hysteretic magnetoresistance loop. The latter facilitates a memory
functionality of such a junction with just a single CMR ferromagnetic layer.
The orientation of the magnetization (stored information) can be read out by
simply measuring the junction resistance in an applied magnetic field. The CMR
facilitates a large read-out signal in a small applied field. We argue that
such a simple single layer CMR junction can operate as a memory cell both in
the superconducting state at cryogenic temperatures and in the normal state up
to room temperature.

###Spintronic oxides grown by laser-MBE|Matthias Opel###

Spintronic oxides grown by laser-MBE. The recent study of oxides led to the discovery of several new fascinating
physical phenomena. High-temperature superconductivity, colossal
magnetoresistance, dilute magnetic doping, or multiferroicity were discovered
and investigated in transition-metal oxides, representing a prototype class of
strongly correlated electronic systems. This development was accompanied by an
enormous progress regarding thin film fabrication. Within the past two decades,
epitaxial thin films with crystalline quality approaching semiconductor
standards became available using laser molecular beam epitaxy. This evolution
is reviewed, particularly with emphasis on transition-metal oxide thin films,
their versatile physical properties, and their impact on the field of
spintronics. First, the physics of ferromagnetic half-metallic oxides, such as
the doped manganites, the double perovskites and magnetite is presented
together with possible applications based on magnetic tunnel junctions. Second,
the wide bandgap semiconductor zinc oxide is discussed particularly with regard
to the controversy of dilute magnetic doping with transition-metal ions and the
possibility of realizing p-type conductivity. Third, the field of oxide
multiferroics is presented with the recent developments in single-phase
multiferroic thin film perovskites as well as in composite multiferroic
hybrids.

###Detection of magnetic gap in the topological surface states of MnBi2Te4|Haoran Ji,Yanzhao Liu,He Wang,Jiawei Luo,Jiaheng Li,Hao Li,Yang Wu,Yong Xu,Jian Wang###

Detection of magnetic gap in the topological surface states of MnBi2Te4. Recently, intrinsic antiferromagnetic topological insulator MnBi2Te4 has
drawn intense research interest and leads to plenty of significant progress in
physics and materials science by hosting quantum anomalous Hall effect, axion
insulator state, and other quantum phases. An essential ingredient to realize
these quantum states is the magnetic gap in the topological surface states
induced by the out-of-plane ferromagnetism on the surface of MnBi2Te4. However,
the experimental observations of the surface gap remain controversial. Here, we
report the observation of the surface gap via the point contact tunneling
spectroscopy. In agreement with theoretical calculations, the gap size is
around 50 meV, which vanishes as the sample becomes paramagnetic with
increasing temperature. The magnetoresistance hysteresis is detected through
the point contact junction on the sample surface with an out-of-plane magnetic
field, substantiating the surface ferromagnetism. Furthermore, the non-zero
transport spin polarization coming from the ferromagnetism is determined by the
point contact Andreev reflection spectroscopy. Combining these results, the
magnetism-induced gap in topological surface states of MnBi2Te4 is revealed.

###Determination of spin relaxation times in heavy metals via 2nd harmonic spin injection magnetoresistance|C. Fang,C. H. Wan,X. M. Liu,B. S. Yang,J. Y. Qin,B. S. Tao,H. Wu,X. Zhang,Z. M. Jin,A. Hoffmann,X. F. Han###

Determination of spin relaxation times in heavy metals via 2nd harmonic spin injection magnetoresistance. In tunnel junctions between ferromagnets and heavy elements with strong spin
orbit coupling the magnetoresistance is often dominated by tunneling
anisotropic magnetoresistance (TAMR). This makes conventional DC spin injection
techniques impractical for determining the spin relaxation time ($\tau_s$).
Here, we show that this obstacle for measurements of $\tau_s$ can be overcome
by 2nd harmonic spin-injection-magnetoresistance (SIMR). In the 2nd harmonic
signal the SIMR is comparable in magnitude to TAMR, thus enabling Hanle-induced
SIMR as a powerful tool to directly determine $\tau_s$. Using this approach we
determined the spin relaxation time of Pt and Ta and their temperature
dependences. The spin relaxation in Pt seems to be governed by Elliott-Yafet
mechanism due to a constant resistivity $\times$spin relaxation time product
over a wide temperature range.

###Combination of informational storage and logical processing based on an all-oxide asymmetric multiferroic tunnel junction|Q. Liu,J. Miao,Z. D. Xu,P. F. Liu,Q. H. Zhang,L. Gu,K. K. Meng,X. G. Xu,J. K. Chen,Y. Wu,Y. Jiang###

Combination of informational storage and logical processing based on an all-oxide asymmetric multiferroic tunnel junction. Multiferroic tunnel junctions (MFTJs) have already been proved to be
promising candidates for application in spintronics devices. The coupling
between tunnel magnetoresistance (TMR) and tunnel electroresistance (TER) in
MFTJs can provide four distinct resistive states in a single memory cell. Here
we show that in an all-oxide asymmetric MFTJ of La0.7Sr0.3MnO3 /PbZr0.2Ti0.8O3
/La0.7Te0.3MnO3 (LSMO/PZT/LTMO) with p-type and n-type electrodes, the
intrinsic rectification is observed and can be modified by the ferroelectric
polarization of PZT. Owing to the combined TMR, TER and diode effects, two
different groups of four resistive states under opposite reading biases are
performed. With two parallel asymmetric junctions and the appropriate series
resistance, the coexistence of logic units and quaternary memory cells can be
realized in the same array devices. The asymmetric MFTJ structure enables more
possibilities for designing next generation of multi-states memory and logical
devices with higher storage density, lower energy consumption and significantly
increased integration level.

###Voltage-controlled inversion of tunnel magnetoresistance in epitaxial Nickel/Graphene/MgO/Cobalt junctions|F. Godel,M. Venkata Kamalakar,B. Doudin,Y. Henry,D. Halley,J. -F. Dayen###

Voltage-controlled inversion of tunnel magnetoresistance in epitaxial Nickel/Graphene/MgO/Cobalt junctions. We report on the fabrication and characterization of vertical spin-valve
structures using a thick epitaxial MgO barrier as spacer layer and a
graphene-passivated Ni film as bottom ferromagnetic electrode. The devices show
robust and scalable tunnel magnetoresistance, with several changes of sign upon
varying the applied bias voltage. These findings are explained by a model of
phonon-assisted transport mechanisms that relies on the peculiarity of the band
structure and spin density of states at the hybrid graphene|Ni interface.

###Magnetic Domain Wall Engineering in a Nanoscale Permalloy Junction|Junlin Wang,Xichao Zhang,Xianyang Lu,Jason Zhang,Hua Ling,Jing Wu,Yan Zhou,Yongbing Xu###

Magnetic Domain Wall Engineering in a Nanoscale Permalloy Junction. Nanoscale magnetic junction provides a useful approach to act as the building
block for magnetoresistive random access memories (MRAM), where one of the key
issues is to control the magnetic domain configuration. Here, we study the
domain structure and the magnetic switching in the Permalloy (Fe20Ni80)
nanoscale magnetic junctions with different thicknesses by using micromagnetic
simulations. It is found that both the 90-degree and 45-degree domain walls can
be formed between the junctions and the wire arms depending on the thickness of
the device. The magnetic switching fields show distinct thickness dependencies
with a broad peak varying from 7 nm to 22 nm depending on the junction sizes,
and the large magnetic switching fields favor the stability of the MRAM
operation.

###Resistive Switching and Voltage Induced Modulation of Tunneling Magnetoresistance in Nanosized Perpendicular Organic Spin Valves|Robert Göckeritz,Nico Homonnay,Alexander Müller,Bodo Fuhrmann,Georg Schmidt###

Resistive Switching and Voltage Induced Modulation of Tunneling Magnetoresistance in Nanosized Perpendicular Organic Spin Valves. Nanoscale multifunctional perpendicular organic spin valves have been
fabricated. The devices based on an La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/Co
trilayer show resistive switching of up to 4-5 orders of magnitude and
magnetoresistance as high as -70% the latter even changing sign when voltage
pulses are applied. This combination of phenomena is typically observed in
multiferroic tunnel junctions where it is attributed to magnetoelectric
coupling between a ferromagnet and a ferroelectric material. Modeling indicates
that here the switching originates from a modification of the
La$_{0.7}$Sr$_{0.3}$MnO$_3$ surface. This modification influences the tunneling
of charge carriers and thus both the electrical resistance and the tunneling
magnetoresistance which occurs at pinholes in the organic layer.

###A Theoretical Study on Spin-Dependent Transport of "Ferromagnet/Carbon Nanotube Encapsulating Magnetic Atoms/Ferromagnet" Junctions with 4-Valued Conductances|Satoshi Kokado,Kikuo Harigaya###

A Theoretical Study on Spin-Dependent Transport of "Ferromagnet/Carbon Nanotube Encapsulating Magnetic Atoms/Ferromagnet" Junctions with 4-Valued Conductances. As a novel function of ferromagnet (FM)/spacer/FM junctions, we theoretically
investigate multiple-valued (or multi-level) cell property, which is in
principle realized by sensing conductances of four states recorded with
magnetization configurations of two FMs; (up,up), (up,down), (down,up),
(down,down). In order to sense all the states, 4-valued conductances
corresponding to the respective states are necessary. We previously proposed
that 4-valued conductances are obtained in FM1/spin-polarized spacer (SPS)/FM2
junctions, where FM1 and FM2 have different spin polarizations, and the spacer
depends on spin [J. Phys.: Condens. Matter 15, 8797 (2003)]. In this paper, an
ideal SPS is considered as a single-wall armchair carbon nanotube encapsulating
magnetic atoms, where the nanotube shows on-resonance or off-resonance at the
Fermi level according to its length. The magnitude of the obtained 4-valued
conductances has an opposite order between the on-resonant nanotube and the
off-resonant one, and this property can be understood by considering electronic
states of the nanotube. Also, the magnetoresistance ratio between (up,up) and
(down,down) can be larger than the conventional one between parallel and
anti-parallel configurations.

###Off-axis electron holography for the direct visualization of perpendicular shape anisotropy in nano-scale 3D magnetic random-access-memory devices|Trevor P. Almeida,Alvaro Palomino,Steven Lequeux,Victor Boureau,Olivier Fruchart,Ioan Lucian Prejbeanu,Bernard Dieny,David Cooper###

Off-axis electron holography for the direct visualization of perpendicular shape anisotropy in nano-scale 3D magnetic random-access-memory devices. Perpendicular shape anisotropy (PSA) and double magnetic tunnel junctions
(DMTJ) offer practical solutions to downscale spin-transfer-torque Magnetic
Random-Access Memory (STT-MRAM) beyond 20 nm technology nodes, whilst retaining
their thermal stability and reducing critical currents applied. However, as
these modern devices become smaller and three-dimensionally (3D) complex, our
understanding of their functional magnetic behavior is often indirect, relying
on magnetoresistance measurements and micromagnetic modelling. In this paper,
we review recent work that was performed on these structures using a range of
advanced electron microscopy techniques, focusing on aspects specific to the 3D
and nanoscale nature of such elements. We present the methodology for the
systematic transfer of individual SST-MRAM nano-pillars from large-scale arrays
to image their magnetic configurations directly using off-axis electron
holography. We show that improved phase sensitivity through stacking of
electron holograms can be used to image subtle variations in DMTJs and the
thermal stability of < 20 nm PSA-STT-MRAM nano-pillars during in-situ heating.
The experimental practicalities, benefits and limits of using electron
holography for analysis of MRAM devices are discussed, unlocking practical
pathways for direct imaging of the functional magnetic performance of these
systems with high spatial resolution and sensitivity.

###Probing Spin Accumulation in Ni/Au/Ni Single-Electron Transistors with Efficient Spin Injection and Detection Electrodes|R. S. Liu,H. Pettersson,L. Michalak,C. M. Canali,L. Samuelson###

Probing Spin Accumulation in Ni/Au/Ni Single-Electron Transistors with Efficient Spin Injection and Detection Electrodes. We have investigated spin accumulation in Ni/Au/Ni single-electron
transistors assembled by atomic force microscopy. The fabrication technique is
unique in that unconventional hybrid devices can be realized with unprecedented
control, including real-time tunable tunnel resistances. A grid of Au discs, 30
nm in diameter and 30 nm thick, is prepared on a SiO2 surface by conventional
e-beam writing. Subsequently, 30 nm thick ferromagnetic Ni source, drain and
side-gate electrodes are formed in similar process steps. The width and length
of the source and drain electrodes were different to exhibit different coercive
switching fields. Tunnel barriers of NiO are realized by sequential Ar and O2
plasma treatment. Using an atomic force microscope with specially designed
software, a single non-magnetic Au nanodisc is positioned into the 25 nm gap
between the source and drain electrodes. The resistance of the device is
monitored in real-time while the Au disc is manipulated step-by-step with
Angstrom-level precision. Transport measurements in magnetic field at 1.7 K
reveal no clear spin accumulation in the device, which can be attributed to
fast spin relaxation in the Au disc. From numerical simulations using the
rate-equation approach of orthodox Coulomb blockade theory, we can put an upper
bound of a few ns on the spin-relaxation time for electrons in the Au disc. To
confirm the magnetic switching characteristics and spin injection efficiency of
the Ni electrodes, we fabricated a test structure consisting of a Ni/NiO/Ni
magnetic tunnel junction with asymmetric dimensions of the electrodes similar
to those of the SETs. Magnetoresistance measurements on the test device
exhibited clear signs of magnetic reversal and a maximum TMR of 10%, from which
we deduced a spin-polarization of about 22% in the Ni electrodes.

###Spin-dependent transport in a multiferroic tunnel junction: Theory for Co/PbTiO$_{3}$/Co|Vladislav S. Borisov,Sergey Ostanin,Steven Achilles,Jürgen Henk,Ingrid Mertig###

Spin-dependent transport in a multiferroic tunnel junction: Theory for Co/PbTiO$_{3}$/Co. Spin-dependent electronic transport through multiferroic Co/PbTiO$_{3}$/Co
tunnel junctions is studied theoretically. Conductances calculated within the
Landauer-B\"uttiker formalism yield both a large tunnel magnetoresistance (TMR)
and a large tunnel electroresistance (TER). On top of this, we establish a
four-conductance state. The conductances depend crucially on the details of the
electronic structure at the interfaces. In particular, the spin polarization of
the tunneling electronic states is affected by the hybridization of orbitals
and the associated charge transfer at both interfaces. Digital doping of the
PbTiO$_{3}$ barrier with Zr impurities at the TiO$_{2}$/Co$_{2}$ interface
significantly enhances the TMR\@. In addition, it removes the metalization of
the barrier.

###Asymmetric Coulomb Oscillation and Giant Anisotropic Magnetoresistance in Doped Graphene Nanojunctions|Subramani Amutha,Arijit Sen###

Asymmetric Coulomb Oscillation and Giant Anisotropic Magnetoresistance in Doped Graphene Nanojunctions. We report here the charge transport behavior in graphene nanojunctions in
which graphene nanodots, with relatively long relaxation time, are interfaced
with ferromagnetic electrodes. Subsequently we explore the effect of
substitutional doping of transition metal atoms in zigzag graphene nanodots
(z-GNDs) on the charge transport under non-collinear magnetization. Only
substitutional doping of transition metal atoms in z-GNDs at certain sites
demonstrates the spin filtering effect with a large tunnelling
magnetoresistance as high as 700%, making it actually suitable for spintronic
applications. From the electrical field simulation around the junction area
within the electrostatic physics model, we find that the value of electric
field strength increases especially with doped graphene nanodots, as the gap
between the gate electrode and tip axis is reduced from 3 nm to 1 nm. Our
detailed analysis further suggests the onset of asymmetric Coulomb oscillations
with varying amplitudes in graphene nanodots, on being doped with magnetic
ions. Such kind of tunability in the electronic conductance can potentially be
exploited in designing spintronic logic gates at nanoscale.

###Substantial reduction of write-error rate for voltage-controlled magnetoresistive random access memory by in-plane demagnetizing field and voltage-induced negative out-of-plane anisotropy field|Rie Matsumoto,Shiniji Yuasa,Hiroshi Imamura###

Substantial reduction of write-error rate for voltage-controlled magnetoresistive random access memory by in-plane demagnetizing field and voltage-induced negative out-of-plane anisotropy field. Voltage-controlled magnetoresistive random access memory (VC-MRAM) based on
voltage-induced dynamic switching in magnetic tunnel junctions (MTJs) is a
promising ultimate non-volatile memory with ultralow power consumption.
However, the dynamic switching in a conventional MTJ is accompanied by a
relatively high write error rate (WER), hindering the reliable operation of
VC-MRAM. Here, we propose a reliable writing scheme using the in-plane
demagnetizing field (IDF) and voltage-induced negative out-of-plane anisotropy
field (NOAF). Numerical simulations based on macrospin model demonstrate that
the voltage-induced NOAF modifies the switching dynamics and increases the
torque due to the IDF, thereby reducing the switching time. The IDF and
voltage-induced NOAF also reduce the mean energy difference between the
magnetization direction at the end of the pulse and the equilibrium direction.
As a result, an appropriate combination of the IDF and voltage-induced NOAF
reduces the WER by one order of magnitude compared with that of the dynamic
switching in a conventional MTJ.

###Skyrmion-mediated Nonvolatile Ternary Memory|Md Mahadi Rajib,Namita Bindal,Ravish Kumar Raj,Brajesh Kumar Kaushik,Jayasimha Atulasimha###

Skyrmion-mediated Nonvolatile Ternary Memory. Multistate memory systems have the ability to store and process more data in
the same physical space as binary memory systems, making them a potential
alternative to existing binary memory systems. In the past, it has been
demonstrated that voltage-controlled magnetic anisotropy (VCMA) based writing
is highly energy-efficient compared to other writing methods used in
non-volatile nano-magnetic binary memory systems. In this study, we introduce a
new, VCMA-based and skyrmion-mediated non-volatile ternary memory system using
a perpendicular magnetic tunnel junction (p-MTJ) in the presence of room
temperature thermal perturbation. We have also shown that ternary states {-1,
0, +1} can be implemented with three magnetoresistance values obtained from a
p-MTJ corresponding to ferromagnetic up, down, and skyrmion state, with 99%
switching probability in the presence of room temperature thermal noise in an
energy-efficient way, requiring ~3 fJ energy on an average for each switching
operation. Additionally, we show that our proposed ternary memory demonstrates
an improvement in area and energy by at least 2X and ~60X respectively,
compared to state-of-the-art spin-transfer torque (STT)-based non-volatile
magnetic multistate memories. Furthermore, these three states can be
potentially utilized for energy-efficient, high-density in-memory quantized
deep neural network implementation.

###Thermal and Electrical Properties of Multiwall Carbon Nanotubes|Wei Yi###

Thermal and Electrical Properties of Multiwall Carbon Nanotubes. In this dissertation, thermal and electrical properties of aligned multiwall
carbon nanotubes (MWNTs) prepared by thermal decomposition of hydrocarbons have
been experimentally studied. The thesis consists of six chapters. Ch1 is an
introduction. In Ch2, sample preparation and characterizations are described.
In Ch3, by using a self-heating 3-Omega method, the specific heat, thermal
diffusivity and thermal conductivity of MWNTs are measured. MWNTs of 20-40 nm
diameter show a linear specific heat over a temperature range of 10-300 K,
suggesting that inter-wall coupling in MWNTs is rather weak compared with that
of graphite. The thermal conductivity shows a crossover from linear temperature
dependence to a square law at ~120K, with a rather low room-temperature
amplitude which may have resulted from structural defects. In Ch4, four-wire
tunneling spectroscopy of junctions between MWNTs and a normal metal is
measured. The Coulomb interactions in the MWNTs give rise to a strong zero-bias
suppression of tunneling density of states that can be fitted numerically with
the environmental quantum-fluctuation theory. At low temperatures, an
asymmetric conductance anomaly near zero bias is observed, which is interpreted
as Fano resonance in the strong tunneling regime. In Ch5, the thermoelectric
power (TEP) and longitudinal magnetoresistance (MR) of MWNTs are measured. A
moderate positive TEP with metallic-like linear temperature dependence is
found, suggesting that the electron-hole symmetry in metallic MWNTs is broken.
Periodic oscillations in MR are observed at 20 mK when a longitudinal magnetic
field is applied. The period of oscillation agrees well with the period h/2e of
Altshuler-Aronov-Spivak (AAS) effect if only the outermost graphene wall
contributes to conductance, clearly indicating quantum-interference effects at
low temperatures. Ch6 presents the main conclusions.

###Co-ordination between Rashba spin-orbital interaction and space charge effect and enhanced spin injection into semiconductors|Wei Wu,Jinbin Li,Yue Yu,S. T. Chui###

Co-ordination between Rashba spin-orbital interaction and space charge effect and enhanced spin injection into semiconductors. We consider the effect of the Rashba spin-orbital interaction and space
charge in a ferromagnet-insulator/semiconductor/insulator-ferromagnet junction
where the spin current is severely affected by the doping, band structure and
charge screening in the semiconductor. In diffusion region, if the the
resistance of the tunneling barriers is comparable to the semiconductor
resistance, the magnetoresistance of this junction can be greatly enhanced
under appropriate doping by the co-ordination between the Rashba effect and
screened Coulomb interaction in the nonequilibrium transport processes within
Hartree approximation.

###Spin-neutral currents for spintronics|Ding-Fu Shao,Shu-Hui Zhang,Ming Li,Chang-Beom Eom,Evgeny Y. Tsymbal###

Spin-neutral currents for spintronics. Electric currents carrying a net spin polarization are widely used in
spintronics, whereas globally spin-neutral currents are expected to play no
role in spin-dependent phenomena. Here we show that, in contrast to this common
expectation, spin-independent conductance in compensated antiferromagnets and
normal metals can be efficiently exploited in spintronics, provided their
magnetic space group symmetry supports a non-spin-degenerate Fermi surface. Due
to their momentum-dependent spin polarization, such antiferromagnets can be
used as active elements in antiferromagnetic tunnel junctions (AFMTJs) and
produce a giant tunneling magnetoresistance (TMR) effect. Using RuO$_{2}$ as a
representative compensated antiferromagnet exhibiting spin-independent
conductance along the [001] direction but a non-spin-degenerate Fermi surface,
we design a RuO$_{2}$/TiO$_{2}$/RuO$_{2}$ (001) AFMTJ, where a globally
spin-neutral charge current is controlled by the relative orientation of the
N\'eel vectors of the two RuO$_{2}$ electrodes, resulting in the TMR effect as
large as ~500%. These results are expanded to normal metals which can be used
as a counter electrode in AFMTJs with a single antiferromagnetic layer or other
elements in spintronic devices. Our work uncovers an unexplored potential of
the materials with no global spin polarization for utilizing them in
spintronics.

###Néel Spin Currents in Antiferromagnets|Ding-Fu Shao,Yuan-Yuan Jiang,Jun Ding,Shu-Hui Zhang,Zi-An Wang,Rui-Chun Xiao,Gautam Gurung,W. J. Lu,Y. P. Sun,Evgeny Y. Tsymbal###

Néel Spin Currents in Antiferromagnets. Ferromagnets are known to support spin-polarized currents that control
various spin-dependent transport phenomena useful for spintronics. On the
contrary, fully compensated antiferromagnets are expected to support only
globally spin-neutral currents. Here, we demonstrate that these globally
spin-neutral currents can represent the N\'eel spin currents, i.e. staggered
spin currents flowing through different magnetic sublattices. The N\'eel spin
currents emerge in antiferromagnets with strong intra-sublattice coupling
(hopping) and drive the spin-dependent transport phenomena such as tunneling
magnetoresistance (TMR) and spin-transfer torque (STT) in antiferromagnetic
tunnel junctions (AFMTJs). Using RuO$_{2}$ and Fe$_{4}$GeTe$_{2}$ as
representative antiferromagnets, we predict that the N\'eel spin currents with
a strong staggered spin-polarization produce a sizable field-like STT capable
of the deterministic switching of the N\'eel vector in the associated AFMTJs.
Our work uncovers the previously unexplored potential of fully compensated
antiferromagnets and paves a new route to realize the efficient writing and
reading of information for antiferromagnetic spintronics.

###First-principles insights into all-optical spin switching in the half-metallic Heusler ferrimagnet Mn$_2$RuGa|G. P. Zhang,Y. H. Bai,M. S. Si,Thomas F. George###

First-principles insights into all-optical spin switching in the half-metallic Heusler ferrimagnet Mn$_2$RuGa. All-optical spin switching (AOS) represents a new frontier in magnetic
storage technology -- spin manipulation without a magnetic field, -- but its
underlying working principle is not well understood. Many AOS ferrimagnets such
as GdFeCo are amorphous and renders the high-level first-principles study
unfeasible. The crystalline half-metallic Heusler Mn$_2$RuGa presents an
opportunity. Here we carry out hitherto the comprehensive density functional
investigation into the material properties of Mn$_2$RuGa, and introduce two
concepts - the spin anchor site and the optical active site - as two pillars
for AOS in ferrimagnets. In Mn$_2$RuGa, Mn$(4a)$ serves as the spin anchor
site, whose band structure is below the Fermi level and has a strong spin
moment, while Mn$(4c)$ is the optical active site whose band crosses the Fermi
level. Our magneto-optical Kerr spectrum and band structure calculation jointly
reveal that the delicate competition between the Ru-$4d$ and Ga-$4p$ states is
responsible for the creation of these two sites. These two sites found here not
only present a unified picture for both Mn$_2$RuGa and GdFeCo, but also open
the door for the future applications. Specifically, we propose a
Mn$_2$Ru$_x$Ga-based magnetic tunnel junction where a single laser pulse can
control magnetoresistance.

###Magnetoresistance and spintronic anisotropy induced by spin excitations along molecular spin chains|K. Katcko,E. Urbain,L. Kandpal,B. Chowrira,F. Schleicher,U. Halisdemir,F. Ngassamnyakam,D. Mertz,B. Leconte,N. Beyer,D. Spor,P. Panissod,A. Boulard,J. Arabski,C. Kieber,E. Sternitsky,V. Da Costa,M. Alouani,M. Hehn,F. Montaigne,A. Bahouka,W. Weber,E. Beaurepaire,D. Lacour,S. Boukari,M. Bowen###

Magnetoresistance and spintronic anisotropy induced by spin excitations along molecular spin chains. Electrically manipulating the quantum properties of nano-objects, such as
atoms or molecules, is typically done using scanning tunnelling microscopes and
lateral junctions. The resulting nanotransport path is well established in
these model devices. Societal applications require transposing this knowledge
to nano-objects embedded within vertical solid-state junctions, which can
advantageously harness spintronics to address these quantum properties thanks
to ferromagnetic electrodes and high-quality interfaces. The challenge here is
to ascertain the device's effective, buried nanotransport path, and to
electrically involve these nano-objects in this path by shrinking the device
area from the macro- to the nano-scale while maintaining high
structural/chemical quality across the heterostructure. We've developed a
low-tech, resist- and solvent-free technological process that can craft
nanopillar devices from entire in-situ grown heterostructures, and use it to
study magnetotransport between two Fe and Co ferromagnetic electrodes across a
functional magnetic CoPc molecular layer. We observe how spin-flip transport
across CoPc molecular spin chains promotes a specific magnetoresistance effect,
and alters the nanojunction's magnetism through spintronic anisotropy. In the
process, we identify three magnetic units along the effective nanotransport
path thanks to a macrospin model of magnetotransport. Our work elegantly
connects the until now loosely associated concepts of spin-flip spectroscopy,
magnetic exchange bias and magnetotransport due to molecular spin chains,
within a solid-state device. We notably measure a 5.9meV energy threshold for
magnetic decoupling between the Fe layer's buried atoms and those in contact
with the CoPc layer forming the so-called 'spinterface'. This provides a first
insight into the experimental energetics of this promising low-power
information encoding unit.

###Sequential tunneling and shot noise in ferromagnet/normal-metal/ferromagnet double tunnel junctions|H. Giang Bach,V. Hung Nguyen,T. Anh Pham###

Sequential tunneling and shot noise in ferromagnet/normal-metal/ferromagnet double tunnel junctions. The tunneling through a ferromagnet/normal metal/ferromagnet double junction
in the Coulomb blockade regime is studied, assuming that the spin relaxation
time of electron in the central metallic island is sufficiently large. Using
the master equation, the current, the tunnel magnetoresistance (TMR), and the
current noise spectrum have been calculated for devices of different
parameters. It was shown that the interplay between spin and charge
correlations strongly depends on the asymmetry of measured device. The charge
correlation makes both the chemical potential shift, which describes the spin
accumulation in the central island, and the TMR oscillated with the same period
as the Coulomb staircase in current-voltage characteristics. This effect is
smeared by the temperature. The spin correlation may cause an enhancement of
noise at finite frequencies, while the zero frequency noise is still always
sub-poissonian. The gate voltage causes an oscillation of not only conductance,
but also TMR and noise.

###Magnetic tunnel junctions with impurities|F. Kanjouri,N. Ryzhanova,B. Dieny,N. Strelkov,A. Vedyayev###

Magnetic tunnel junctions with impurities. The influence of impurities, embedded into the isolating spacer (I) between
two ferromagnetic electrodes (F), on the I-V curve and tunnel magnetoresistance
(TMR), is theoretically investigated. It is shown, that the current and TMR are
strongly enhanced in the vicinity of the impurity under the condition that the
energy of the electron's bound state on the impurity is close to the Fermi
energy. If the position of the impurity inside the barrier is asymmetric, e.g.
closer to the one of the interfaces F/I the I-V curve exhibits quasidiode
behavior.

###Effects of impurity on tunnel magnetoresistance in a ferromagnetic electrode/carbon nanotube/ferromagnetic electrode junctio|A. Ahmadi Fouladi,J. Vahedi,M. Soleymani###

Effects of impurity on tunnel magnetoresistance in a ferromagnetic electrode/carbon nanotube/ferromagnetic electrode junctio. Effects of impurity on the spin-dependent transport in a single wall carbon
nanotube spin-valve, as ferromagnetic electrode/carbon nanotube/ferromagnetic
electrode model junction is numerically investigated. Using a generalized
Green's function method and the Landauer-Buttiker formalism, the impurity
conditions are determined by randomly substitution of carbon atoms in the
honeycomb carbon nanotube lattice by nitrogen and boron atoms. We have found
that transport characteristics, including the spin-dependent current and tunnel
magnetoresistance are strongly influenced by the impurity effects. We think
that the results of the present report could be useful for designing the future
spintronic devices.

###Robust coupling of superconducting order parameter in a mesoscale NbN-Fe-NbN epitaxial structure|S. K. Bose,R. C. Budhani###

Robust coupling of superconducting order parameter in a mesoscale NbN-Fe-NbN epitaxial structure. We report an unconventional and promising route to self-assemble distributed
superconductor-ferromagnet-superconductor (S-F-S) Josephson Junctions on single
crystal [100] MgO. These structures consist of [110] epitaxial nano-plaquettes
of Fe covered with superconducting NbN films of varying thickness. The S-F-S
structures are characterized by strong magnetoresistance (MR) anisotropy for
the in-plane and out-of-plane magnetic fields. The stronger in-plane MR
suggests decoherence of S-F-S junctions whose critical current follows a
(1-T/Tc) and (1-T/Tc)1/2 dependence for T Tc and T<<Tc respectively, in
accordance with the theory of supercurrent transport in such junctions.

###Spin-Polarized Tunneling through Chemical Vapor Deposited Multilayer Molybdenum Disulfide|André Dankert,Parham Pashaei,M. Venkata Kamalakar,Anand P. S. Gaur,Satyaprakash Sahoo,Ivan Rungger,Awadhesh Narayan,Kapildeb Dolui,Anamul Hoque,Michel P. de Jong,Ram S. Katiyar,Stefano Sanvito,Saroj P. Dash###

Spin-Polarized Tunneling through Chemical Vapor Deposited Multilayer Molybdenum Disulfide. The two-dimensional (2D) semiconductor molybdenum disulfide (MoS2) has
attracted widespread attention for its extraordinary electrical, optical, spin
and valley related properties. Here, we report on spin polarized tunneling
through chemical vapor deposited (CVD) multilayer MoS2 (~7 nm) at room
temperature in a vertically fabricated spin-valve device. A tunnel
magnetoresistance (TMR) of 0.5 - 2 % has been observed, corresponding to spin
polarization of 5 - 10 % in the measured temperature range of 300 - 75 K. First
principles calculations for ideal junctions results in a tunnel
magnetoresistance up to 8 %, and a spin polarization of 26 %. The detailed
measurements at different temperatures and bias voltages, and density
functional theory calculations provide information about spin transport
mechanisms in vertical multilayer MoS2 spin-valve devices. These findings form
a platform for exploring spin functionalities in 2D semiconductors and
understanding the basic phenomenon that control their performance.

###Electron space charge effect on spin injection into semiconductors|Yue Yu,Jinbin Li,S. T. Chui###

Electron space charge effect on spin injection into semiconductors. We consider spin polarized transport in a
ferromagnet-insulator/semiconductor/insulator-ferromagnet (F1-I-S-I-F2)
junction. We find that the spin current is strongly dependent on the spin
configurations, the doping and space charge distribution in the semiconductor.
When the ferromagnet-semiconductor interface resistance is comparable to the
semiconductor resistance, the magnetoresistance ratio of this junction can be
greatly enhanced under appropriate doping when the space charge effect in the
nonequilibrium transport processes is taken into consideration.

###Current-induced magnetization dynamics in single and double layer magnetic nanopillars grown by molecular beam epitaxy|N. Müsgens,E. Maynicke,M. Weidenbach,C. J. P. Smits,M. Bückins,J. Mayer,B. Beschoten,G. Güntherodt###

Current-induced magnetization dynamics in single and double layer magnetic nanopillars grown by molecular beam epitaxy. Molecular beam epitaxy is used to fabricate magnetic single and double layer
junctions which are deposited in prefabricated nanostencil masks. For all Co |
Cu | Co double layer junctions we observe a stable intermediate resistance
state which can be reached by current starting from the parallel configuration
of the respective ferromagnetic layers. The generation of spin waves is
investigated at room temperature in the frequency domain by spectrum analysis,
demonstrating both in-plane and out-of-plane precessions of the magnetization
of the free magnetic layer. Current-induced magnetization dynamics in magnetic
single layer junctions of Cu | Co | Cu has been investigated in magnetic fields
which are applied perpendicular to the magnetic layer. We find a hysteretic
switching in the current sweeps with resistance changes significantly larger
than the anisotropic magnetoresistance effect.

###Rashba spin-orbit coupling enhanced magnetoresistance in junctions with one ferromagnet|Chenghao Shen,Ranran Cai,Alex Matos-Abiague,Wei Han,Jong E. Han,Igor Zutic###

Rashba spin-orbit coupling enhanced magnetoresistance in junctions with one ferromagnet. We explain how Rashba spin-orbit coupling (SOC) in a two-dimensional electron
gas (2DEG), or in a conventional $s$-wave superconductor, can lead to a large
magnetoresistance even with one ferromagnet. However, such enhanced
magnetoresistance is not generic and can be nonmonotonic and change its sign
with Rashba SOC. For an in-plane rotation of magnetization, it is typically
negligibly small for a 2DEG and depends on the perfect transmission which
emerges from a spin-parity-time symmetry of the scattering states, while this
symmetry is generally absent from the Hamiltonian of the system. The key
difference from considering the normal-state magnetoresistance is the presence
of the spin-dependent Andreev reflection at superconducting interfaces. In the
fabricated junctions of quasi-2D van der Waals ferromagnets with conventional
$s$-wave superconductors (Fe$_{0.29}$TaS$_2$/NbN) we find another example of
enhanced magnetoresistance where the presence of Rashba SOC reduces the
effective interfacial strength and is responsible for an equal-spin Andreev
reflection. The observed nonmonotonic trend in the out-of-plane
magnetoresistance with the interfacial barrier is an evidence for the
proximity-induced equal-spin-triplet superconductivity.

###Magnetocapacitance and exponential magnetoresistance in manganite-titanate heterojunctions|N. Nakagawa,M. Asai,Y. Mukunoki,T. Susaki,H. Y. Hwang###

Magnetocapacitance and exponential magnetoresistance in manganite-titanate heterojunctions. We present a rectifying manganite-titanate heterojunction exhibiting a
magnetic field tunable depletion layer. This creates a large positive
magnetocapacitance, a direct measure of the field-induced reduction of the
effective depletion width across the junction. Furthermore, the reduction of
the junction barrier shifts the forward bias characteristics, giving
exponentially-enhanced differential magnetoresistance, occurring despite the
absence of a spin filter. These results provide a unique probe of a Mott
insulator/band insulator interface, and further suggest new electronic devices
incorporating the magnetic field sensitivity of these strongly correlated
electron materials.

###Anomalous magnetoresistance on the topological surface|Takehito Yokoyama,Yukio Tanaka,Naoto Nagaosa###

Anomalous magnetoresistance on the topological surface. We investigate charge transport in two-dimensional ferromagnet/feromagnet
junction on a topological insulator. The conductance across the interface
depends sensitively on the directions of the magnetizations of the two
ferromagnets, showing anomalous behaviors compared with the conventional
spin-valve. It is found that the conductance depends strongly on the in-plane
direction of the magnetization. Moreover, in sharp contrast to the conventional
magnetoresistance effect, in the p-n junction, the conductance at the parallel
configuration is much smaller than that at the antiparallel configuration. This
stems from the way how the wavefunctions connect between both sides.

###Spin-transfer in bilayer magnetic nanopillars at high fields as a function of free layer thickness|W. Chen,A. D. Kent,M. J. Rooks,N. Ruiz,J. Z. Sun###

Spin-transfer in bilayer magnetic nanopillars at high fields as a function of free layer thickness. Spin transfer in asymmetric Co/Cu/Co bilayer magnetic nanopillars junctions
has been studied at low temperature as a function of free-layer thickness. The
phase diagram for current-induced magnetic excitations has been determined for
magnetic fields up to 7.5 T applied perpendicular to the junction surface and
free-layers thicknesses from 2 to 5 nm. The junction magnetoresistance is
independent of thickness. The critical current for magnetic excitations
decreases linearly with decreasing free-layer thickness, but extrapolates to a
finite critical current in the limit of zero thickness. The limiting current is
in quantitative agreement with that expected due to a spin-pumping contribution
to the magnetization damping. It may also be indicative of a decrease in the
spin-transfer torque efficiency in ultrathin magnetic layers.

###Resonant electronic states and I-V curves of Fe/MgO/Fe(100) tunnel junctions|Ivan Rungger,Oleg N. Mryasov,Stefano Sanvito###

Resonant electronic states and I-V curves of Fe/MgO/Fe(100) tunnel junctions. The bias dependence of the tunnel magnetoresistance (TMR) of Fe/MgO/Fe tunnel
junctions is investigated theoretically with a fully self-consistent scheme
that combines the non-equilibrium Green's functions method with density
functional theory. At voltages smaller than 20 mVolt the I-V characteristics
and the TMR are dominated by resonant transport through narrow interface states
in the minority spin-band. In the parallel configuration this contribution is
quenched by a voltage comparable to the energy width of the interface state,
whereas it persists at all voltages in the anti-parallel configuration. At
higher bias the transport is mainly determined by the relative positions of the
$\Delta_1$ band-edges in the two Fe electrodes, which causes a decrease of the
TMR.

###Interface Effects on Tunneling Magnetoresistance in Organic Spintronics with Flexible Amine-Au Links|Narjes Gorjizadeh,Su Ying Quek###

Interface Effects on Tunneling Magnetoresistance in Organic Spintronics with Flexible Amine-Au Links. Organic spintronics is a promising emerging field, but the sign of the
tunneling magnetoresistance (TMR) is highly sensitive to interface effects, a
crucial hindrance to applications. A key breakthrough in molecular electronics
was the discovery of amine-Au link groups that give reproducible conductance.
Using first principles calculations, we predict that amine-Au links give
improved reproducibility in organic spintronics junctions with Au-covered Fe
leads. The Au layers allow only states with sp character to tunnel into the
molecule, and the flexibility of amine-Au links results in a narrow range of
TMR for fixed number of Au layers. Even as the Au thickness changes, TMR
remains positive as long as the number of Au layers is the same on both sides
of the junction. Since the number of Au layers on Fe surfaces or Fe
nanoparticles can now be experimentally controlled, amine-Au links provide a
route towards robust TMR in organic spintronics.

###Magnetoresistance Effect in Spin-Polarized Junctions of Ferromagnetically Contacting Multiple Conductive Paths: Applications to Atomic Wires and Carbon Nanotubes|Satoshi Kokado,Kikuo Harigaya###

Magnetoresistance Effect in Spin-Polarized Junctions of Ferromagnetically Contacting Multiple Conductive Paths: Applications to Atomic Wires and Carbon Nanotubes. For spin-polarized junctions of ferromagnetically contacting multiple
conductive paths, such as ferromagnet (FM)/atomic wires/FM and FM/carbon
nanotubes/FM junctions, we theoretically investigate spin-dependent transport
to elucidate the intrinsic relation between the number of paths and conduction,
and to enhance the magnetoresistance (MR) ratio. When many paths are randomly
located between the two FMs, electronic wave interference between the FMs
appears, and then the MR ratio increases with increasing number of paths.
Furthermore, at each number of paths, the MR ratio for carbon nanotubes becomes
larger than that for atomic wires, reflecting the characteristic shape of
points in contact with the FM.

###Giant tunable magnetoresistance of electrically gated graphene ribbon with lateral interface under magnetic field|A. M. Kadigrobov###

Giant tunable magnetoresistance of electrically gated graphene ribbon with lateral interface under magnetic field. Quantum dynamics and kinetics of electrically gated graphene ribbons with
lateral n-p and e-n-p junctions under magnetic field are investigated. It is
shown that the snake-like states of quasiparticles skipping along the n-p
interface do not manifest themselve in the main semiclassical part of the
ribbon conductance. Giant oscillations of the conductance of a ribbon with an
n-p-n junction are predicted and analytically calculated. Depending on the
number of junctions inside the ribbon its magnetoresistance may be controllably
changed by 50% - 90% by an extremely small change of the magnetic field or the
gate voltage.

###Spin-Polarized Transport in Ferromagnet-Marginal Fermi Liquid Systems|Hai-Feng Mu,Gang Su,Qing-Rong Zheng,Biao Jin###

Spin-Polarized Transport in Ferromagnet-Marginal Fermi Liquid Systems. Spin-polarized transport through a marginal Fermi liquid (MFL) which is
connected to two noncollinear ferromagnets via tunnel junctions is discussed in
terms of the nonequilibrium Green function approach. It is found that the
current-voltage characteristics deviate obviously from the ohmic behavior, and
the tunnel current increases slightly with temperature, in contrast to those of
the system with a Fermi liquid. The tunnel magnetoresistance (TMR) is observed
to decay exponentially with increasing the bias voltage, and to decrease slowly
with increasing temperature. With increasing the coupling constant of the MFL,
the current is shown to increase linearly, while the TMR is found to decay
slowly. The spin-valve effect is observed.

###Perpendicular magnetic anisotropy in ultra-thin Cu$_2$Sb-type (Mn-Cr)AlGe films onto thermally oxidized silicon substrates|Takahide Kubota,Keita Ito,Rie Y Umetsu,Koki Takanashi###

Perpendicular magnetic anisotropy in ultra-thin Cu$_2$Sb-type (Mn-Cr)AlGe films onto thermally oxidized silicon substrates. Perpendicularly magnetized films showing small saturation magnetization,
$M_\mathrm{s}$, are essential for spin-transfer-torque writing type
magnetoresistive random access memories, STT-MRAMs. An intermetallic compound,
{(Mn-Cr)AlGe} of the Cu$_2$Sb-type crystal structure was investigated, in this
study, as a material showing the low $M_\mathrm{s}$ ($\sim 300$ kA/m) and
high-perpendicular magnetic anisotropy, $K_\mathrm{u}$. The layer thickness
dependence of $K_\mathrm{u}$ and effects of Mg-insertion layers at top and
bottom (Mn-Cr)AlGe$|$MgO interfaces were studied in film samples fabricated
onto thermally oxidized silicon substrates to realize high-$K_\mathrm{u}$ in
the thickness range of a few nanometer. Optimum Mg-insertion thicknesses were
1.4 and 3.0 nm for the bottom and the top interfaces, respectively, which were
relatively thick compared to results in similar insertion effect investigations
on magnetic tunnel junctions reported in previous studies. The cross-sectional
transmission electron microscope images revealed that the Mg-insertion layers
acted as barriers to interdiffusion of Al-atoms as well as oxidization from the
MgO layers. The values of $K_\mathrm{u}$ were about $7 \times 10^5$ and $2
\times 10^5$ J/m$^3$ at room temperature for 5 and 3 nm-thick (Mn-Cr)AlGe
films, respectively, with the optimum Mg-insertion thicknesses. The
$K_\mathrm{u}$ at a few nanometer thicknesses is comparable or higher than
those reported in perpendicularly magnetized CoFeB films which are
conventionally used in MRAMs, while the $M_\mathrm{s}$ value is one third or
less smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are
promising from the viewpoint of not only the magnetic properties, but also the
compatibility to the silicon process in the film fabrication.

###Order parameter dynamics in Mn$_3$Sn driven by DC and pulsed spin-orbit torques|Ankit Shukla,Siyuan Qian,Shaloo Rakheja###

Order parameter dynamics in Mn$_3$Sn driven by DC and pulsed spin-orbit torques. We numerically investigate and develop analytic models for both the DC and
pulsed spin-orbit-torque (SOT)-driven response of order parameter in
single-domain Mn$_3$Sn, which is a metallic antiferromagnet with an anti-chiral
120$^\circ$ spin structure. We show that DC currents above a critical threshold
can excite oscillatory dynamics of the order parameter in the gigahertz to
terahertz frequency spectrum. Detailed models of the oscillation frequency
versus input current are developed and found to be in excellent agreement with
the numerical simulations of the dynamics. In the case of pulsed excitation,
the magnetization can be switched from one stable state to any of the other
five stable states in the Kagome plane by tuning the duration or the amplitude
of the current pulse. Precise functional forms of the final switched state
versus the input current are derived, offering crucial insights into the
switching dynamics of Mn$_3$Sn. The readout of the magnetic state can be
carried out via either the anomalous Hall effect, or the recently demonstrated
tunneling magnetoresistance in an all-Mn$_3$Sn junction. We also discuss
possible disturbance of the magnetic order due to heating that may occur if the
sample is subject to large currents. Operating the device in pulsed mode or
using low DC currents reduces the peak temperature rise in the sample due to
Joule heating. Our predictive modeling and simulation results can be used by
both theorists and experimentalists to explore the interplay of SOT and the
order dynamics in Mn$_3$Sn, and to further benchmark the device performance.

###Spin-polarized bipolar transport and its applications|S. Das Sarma,Jaroslav Fabian,Igor Zutic###

Spin-polarized bipolar transport and its applications. In spin-polarized bipolar transport both electrons and holes in doped
semiconductors contribute to spin-charge coupling. The current conversion
between the minority (as referred to carriers and not spin) and majority
carriers leads to novel spintronic schemes if nonequilibrium spin is present.
Most striking phenomena occur in inhomogeneously doped magnetic {\it p-n}
junctions, where the presence of nonequilibrium spin at the depletion layer
leads to the spin-voltaic effect: electric current flows without external bias,
powered only by spin. The spin-voltaic effect manifests itself in giant
magnetoresistance of magnetic {\it p-n} junctions, where the relative change of
the magnitude of electric current upon reversing magnetic field can be more
than 1000%. The paper reviews nonmagnetic and magnetic spin-polarized {\it p-n}
junctions, formulates the essentials of spin-polarized bipolar transport as
carrier recombination and spin relaxation limited drift and diffusion, and
discusses specific device schemes of spin-polarized solar cells and magnetic
diodes.

###A model for spin-polarized transport in perovskite manganite bi-crystal grain boundaries|R. Gunnarsson,A. Kadigrobov,Z. Ivanov###

A model for spin-polarized transport in perovskite manganite bi-crystal grain boundaries. We have studied the temperature dependence of low-field magnetoresistance and
current-voltage characteristics of a low-angle bi-crystal grain boundary
junction in perovskite manganite La_{2/3}Sr_{1/3}MnO_3 thin film. By gradually
trimming the junction we have been able to reveal the non-linear behavior of
the latter. With the use of the relation M_{GB} \propto M_{bulk}\sqrt{MR^*} we
have extracted the grain boundary magnetization. Further, we demonstrate that
the built-in potential barrier of the grain boundary can be modelled by
V_{bi}\propto M_{bulk}^2 - M_{GB}^2. Thus our model connects the
magnetoresistance with the potential barrier at the grain boundary region. The
results indicate that the band-bending at the grain boundary interface has a
magnetic origin.

###Two-terminal spin-orbit torque magnetoresistive random access memory|Noriyuki Sato,Fen Xue,Robert M. White,Chong Bi,Shan X. Wang###

Two-terminal spin-orbit torque magnetoresistive random access memory. Spin-transfer torque magnetoresistive random access memory (STT-MRAM) is an
attractive alternative to current random access memory technologies due to its
non-volatility, fast operation and high endurance. STT-MRAM does though have
limitations including the stochastic nature of the STT-switching and a high
critical switching current, which makes it unsuitable for ultrafast operation
at nanosecond and sub-nanosecond regimes. Spin-orbit torque (SOT) switching,
which relies on the torque generated by an in-plane current, has the potential
to overcome these limitations. However, SOT-MRAM cells studied so far use a
three-terminal structure in order to apply the in-plane current, which
increases the size of the cells. Here we report a two-terminal SOT-MRAM cell
based on a CoFeB/MgO magnetic tunnel junction pillar on an ultrathin and narrow
Ta underlayer. In this device, an in-plane and out-of-plane current are
simultaneously generated upon application of a voltage, and we demonstrate that
the switching mechanism is dominated by SOT. We also compare our device to a
STT-MRAM cell built with the same architecture and show that critical write
current in the SOT-MRAM cell is reduced by more than 70%.

###Theory of spin-polarized bipolar transport in magnetic p-n junctions|Jaroslav Fabian,Igor Zutic,S. Das Sarma###

Theory of spin-polarized bipolar transport in magnetic p-n junctions. The interplay between spin and charge transport in electrically and
magnetically inhomogeneous semiconductor systems is investigated theoretically.
In particular, the theory of spin-polarized bipolar transport in magnetic p-n
junctions is formulated, generalizing the classic Shockley model. The theory
assumes that in the depletion layer the nonequilibrium chemical potentials of
spin up and spin down carriers are constant and carrier recombination and spin
relaxation are inhibited. Under the general conditions of an applied bias and
externally injected (source) spin, the model formulates analytically carrier
and spin transport in magnetic p-n junctions at low bias. The evaluation of the
carrier and spin densities at the depletion layer establishes the necessary
boundary conditions for solving the diffusive transport equations in the bulk
regions separately, thus greatly simplifying the problem. The carrier and spin
density and current profiles in the bulk regions are calculated and the I-V
characteristics of the junction are obtained. It is demonstrated that spin
injection through the depletion layer of a magnetic p-n junction is not
possible unless nonequilibrium spin accumulates in the bulk regions--either by
external spin injection or by the application of a large bias. Implications of
the theory for majority spin injection across the depletion layer, minority
spin pumping and spin amplification, giant magnetoresistance, spin-voltaic
effect, biasing electrode spin injection, and magnetic drift in the bulk
regions are discussed in details, and illustrated using the example of a GaAs
based magnetic p-n junction.

###Coexistance of giant tunneling electroresistance and magnetoresistance in an all-oxide magnetic tunnel junction|Nuala Mai Caffrey,Thomas Archer,Ivan Rungger,Stefano Sanvito###

Coexistance of giant tunneling electroresistance and magnetoresistance in an all-oxide magnetic tunnel junction. We demonstrate with first-principles electron transport calculations that
large tunneling magnetoresistance (TMR) and tunneling electroresistance (TER)
effects can coexist in an all-oxide device. The TMR originates from the
symmetry-driven spin filtering provided by the insulating BaTiO3 barrier to the
electrons injected from SrRuO3. In contrast the TER is possible only when a
thin SrTiO3 layer is intercalated at one of the SrRuO3/BaTiO3 interfaces. As
the complex band-structure of SrTiO3 has the same symmetry than that of BaTiO3,
the inclusion of such an intercalated layer does not negatively alter the TMR
and in fact increases it. Crucially, the magnitude of the TER also scales with
the thickness of the SrTiO3 layer. The SrTiO3 thickness becomes then a single
control parameter for both the TMR and the TER effect. This protocol offers a
practical way to the fabrication of four-state memory cells.

###Anisotropic proximity-induced superconductivity and edge supercurrent in Kagome metal, K1-xV3Sb5|Yaojia Wang,Shuoying Yang,Pranava K. Sivakumar,Brenden R. Ortiz,Samuel M. L. Teicher,Heng Wu,Abhay K. Srivastava,Chirag Garg,Defa Liu,Stuart S. P. Parkin,Eric S. Toberer,Tyrel McQueen,Stephen D. Wilson,Mazhar N. Ali###

Anisotropic proximity-induced superconductivity and edge supercurrent in Kagome metal, K1-xV3Sb5. Materials with transition metals in triangular lattices are of great interest
for their potential combination of strong correlation, exotic magnetism and
electronic topology. Kagome nets are of particular importance since the
discovery of geometrically frustrated magnetism and topological band structures
in crystals like Herbertsmithite and Fe3Sn2, respectively. KV3Sb5 was
discovered to be a layered topological metal with a Kagome net of vanadium.
Here, we fabricated Josephson Junctions (JJ) of K1-xV3Sb5 and induced
superconductivity over long junction lengths. Through magnetoresistance and
current vs. phase measurements, we observed magnetic field sweeping direction
dependent magnetoresistance, and an anisotropic interference pattern with a
Fraunhofer pattern for in-plane magnetic field, but a suppression of critical
current for out-of-plane magnetic field. These results indicate an anisotropic
internal magnetic field in K1-xV3Sb5 which influences the superconducting
coupling in the junction, possibly giving rise to spin-triplet
superconductivity. In addition, the observation of long-lived fast oscillations
shows evidence of spatially localized conducting channels arising from edge
states. These observations pave the way for studying unconventional
superconductivity and Josephson device based on Kagome metals with electron
correlation and topology.

###Electron transport in a ferromagnetic/normal/ferromagnetic tunnel junction based on the surface of a topological insulator|Jian-Hui Yuan,Yan Zhang,Jian-Jun Zhang,Ze Cheng###

Electron transport in a ferromagnetic/normal/ferromagnetic tunnel junction based on the surface of a topological insulator. We theoretically study the electron transport properties in a
ferromagnetic/normal/ferromagnetic tunnel junction, which is deposited on the
top of a topological surface. The conductance at the parallel (\textbf{P})
configuration can be much bigger than that at the antiparallel (\textbf{AP})
configuration. Compared \textbf{P} with \textbf{AP} configuration, there exists
a shift of phase which can be tuned by gate voltage. We find that the exchange
field weakly affects the conductance of carriers for \textbf{P} configuration
but can dramatically suppress the conductance of carriers for \textbf{AP}
configuration. This controllable electron transport implies anomalous
magnetoresistance in this topological spin valve, which may contribute to the
development of spintronics . In addition, we find that there is a
Fabry-Perot-like electron interference.

###Electron-electron interaction effects on transport through mesoscopic superconducting hybrid junctions|Arijit Saha###

Electron-electron interaction effects on transport through mesoscopic superconducting hybrid junctions. Effects due to the proximity of a superconductor has motivated a lot of
research work in the last several decades both from theoretical and
experimental point of view. In this review we are going to describe the physics
of systems containing normal metal-superconductor interface. Mainly we discuss
transport properties through such hybrid structures. In particular, we describe
the effects of electron electron interaction on transport through such
superconducting junction of multiple one-dimensional quantum wires. The latter
can be described in terms of a non-Fermi liquid theory called Luttinger liquid.
In this review, from the application point of view, we also demonstrate the
possible scenarios for production of pure spin current and large tunnelling
magnetoresistance in such hybrid junctions and analyze the influence of
electron-electron interaction on the stability of the production of pure spin
current.

###Subgap tunneling via quantum-interference effect: insulators and charge density waves|S. Duhot,R. Mélin###

Subgap tunneling via quantum-interference effect: insulators and charge density waves. A quantum interference effect is discussed for subgap tunneling over a
distance comparable to the coherence length, which is a consequence of
``advanced-advanced'' and ``retarded-retarded'' transmission modes [Altland and
Zirnbauer, Phys. Rev. B 55, 1142 (1997)]. Effects typical of disorder are
obtained from the interplay between multichannel averaging and higher order
processes in the tunnel amplitudes. Quantum interference effects similar to
those occurring in normal tunnel junctions explain magnetoresistance
oscillations of a CDW pierced by nanoholes [Latyshev et al., Phys. Rev. Lett.
78, 919 (1997)], having periodicity h/2e as a function of the flux enclosed in
the nanohole. Subgap tunneling is coupled to the sliding motion by charge
accumulation in the interrupted chains. The effect is within the same trend as
random matrix theory for normal metal-CDW hybrids [Visscher et al., Phys. Rev.
B 62, 6873 (2000)]. We suggest that the experiment by Latyshev et al. probes
weak localization-like properties of evanescent quasiparticles, not an
interference effect related to the quantum mechanical ground state.

###Current-Perpendicular-to-Plane Giant Magnetoresistance Effect in van der Waals Heterostructures|Xinlu Li,Yurong Su,Meng Zhu,Fanxing Zheng,Peina Zhang,Jia Zhang,Jing-Tao Lü###

Current-Perpendicular-to-Plane Giant Magnetoresistance Effect in van der Waals Heterostructures. Spin-dependent transport in a full van der Waals (vdW) giant
magnetoresistance (GMR) junctions with the structure of Fe3GeTe2/XTe2/Fe3GeTe2
(X = Pt, Pd) has been investigated by using first-principles calculations. The
ballistic conductance, magnetoresistance (MR) and resistance-area product (RA)
have been calculated in a current-perpendicular-to-plane (CPP) geometry. A
giant magnetoresistance of around 2000% and RA less than 0.3 {\Omega} {\mu}m2
have been found in the proposed vdW CPP GMR. In addition, the spin-orbit
coupling effect on transport and anisotropy magnetoresistance (AMR) has also
been investigated. The calculated AMR is found to be around 20% in
Fe3GeTe2/trilayer-PdTe2/Fe3GeTe2 CPP GMR. Both GMR and AMR in the proposed vdW
CPP GMR mainly originate from the bulk electronic structure properties of
Fe3GeTe2. This work demonstrates a vdW CPP GMR with superior advantages
including perpendicular magnetic anisotropy, large GMR, low RA as well as
sizable AMR may stimulate future experimental explorations and should be
appealing for their applications in spintronic devices including magnetic
sensor and memory.

###Point Contact Spin Spectroscopy of Ferromagnetic MnAs Epitaxial Films|R. Panguluri,G. Tsoi,B. Nadgorny,S. H. Chun,N. Samarth,I. I. Mazin###

Point Contact Spin Spectroscopy of Ferromagnetic MnAs Epitaxial Films. We use point contact Andreev reflection spin spectroscopy to measure the
transport spin polarization of MnAs epitaxial films grown on (001) GaAs. By
analyzing both the temperature dependence of the contact resistance and the
phonon spectra of lead acquired simultaneously with the spin polarization
measurements, we demonstrate that all the point contacts are in the ballistic
limit. A ballistic transport spin polarization of approximately 49% and 44% is
obtained for the type A and type B orientations of MnAs, respectively. These
measurements are consistent with our density functional calculations, and with
recent observations of a large tunnel magnetoresistance in MnAs/AlAs/(Ga,Mn)As
tunnel junctions.

###Pseudospin-valve effect on transport in junctions of three-dimensional topological insulator surfaces|Sthitadhi Roy,Krishanu Roychowdhury,Sourin Das###

Pseudospin-valve effect on transport in junctions of three-dimensional topological insulator surfaces. We show that the surface states of pristine 3D topological insulators (TIs)
are analogs of ferromagnetic half metals due to complete polarization of an
emergent momentum independent pseudospin (SU(2)) degree of freedom on the
surface. To put this claim on firm footing, we present results for TI surfaces
perpendicular to the crystal growth axis, which clearly show that the tunneling
conductance between two such TI surfaces of the same TI material is dominated
by this half metallic behavior leading to physics reminiscent of a spin-valve.
Further using the generalized tunnel magnetoresistance derived in this work we
also study the tunneling current between arbitrary TI surfaces. We also perform
a comprehensive study of the effect of all possible surface potentials allowed
by time reversal symmetry on this spin-valve effect and show that it is robust
against most of such potentials.

###Spin-transfer-induced excitations in bilayer magnetic nanopillars at high fields: The effects of contact layers|Wenyu Chen,Andrew D. Kent,M. J. Rooks,N. Ruiz,Jonathan Z. Sun###

Spin-transfer-induced excitations in bilayer magnetic nanopillars at high fields: The effects of contact layers. Current-induced excitations in bilayer magnetic nanopillars have been studied
with large magnetic fields applied perpendicular to the layers at low
temperature. Junctions investigated all have Cu/Co/Cu/Co/Cu as core layer
stacks. Two types of such junctions are compared, one with the core stack
sandwiched between Pt layers (type A), the other with Pt only on one side of
the stack (type B). Transport measurements show that these two types of
junctions have similar magnetoresistance and slope of critical current with
respect to field, while A samples have higher resistance. The high-field
bipolar excitation, as was previously reported [Oezyilmaz et al., Phys. Rev. B
71, 140403(R) (2005)], is present in B samples only. This illustrates the
importance of contact layers to spin-current-induced phenomena. This also
confirms a recent prediction on such spin-wave excitations in bilayers.

###Scattering theory of magnetic/superconducting junctions with spin active interfaces|F. Romeo,R. Citro###

Scattering theory of magnetic/superconducting junctions with spin active interfaces. We formulate a generalized scattering field theory a la Buttiker describing
particles transport in magnetic/superconducting heterostructures. The proposed
formalism, characterized by a four- component spinorial wavefunction of the
Bogoliubov de Gennes theory, allows to describe the spin flipping phenomena
induced by noncollinear magnetizations in the scattering region. As a specific
application of the theory, we analyze the conductance, the magnetoresistance
and the generation of spin-torque produced by an applied voltage in a
spin-valve system. Quantum size effects and quantum beating patterns both in
the conductance and in the spin-torque are carefully described.

###Studying angle-dependent magnetoresistance oscillations of cuprate superconductors in a model with antiferromagnetic reconstruction and magnetic breakdown|Sylvia K. Lewin,James G. Analytis###

Studying angle-dependent magnetoresistance oscillations of cuprate superconductors in a model with antiferromagnetic reconstruction and magnetic breakdown. We calculate angle-dependent magnetoresistance oscillations (AMRO) for
interlayer transport of cuprate superconductors in the presence of ($\pi,\pi$)
order. The order reconstructs the Fermi surface, creating magnetic breakdown
junctions; we show how such magnetic breakdown effects can be incorporated into
calculations of interlayer conductivity for this system. We successfully fit
experimental data with our model, and these fits suggest a connection between
($\pi,\pi$) order and the anisotropic scattering observed in overdoped
cuprates. This work paves the way for the use of AMRO as a tool to distinguish
different kinds of ordered states.

###Giant Magnetoresistance in Bilayer Graphene Nanoflakes|R. Farghadan,M. Farekiyan###

Giant Magnetoresistance in Bilayer Graphene Nanoflakes. Coherent spin transport through bilayer graphene (BLG) nanoflakes sandwiched
between two electrodes made of single-layer zigzag graphene nanoribbon was
investigated by means of Landauer-Buttiker formalism. Application of a magnetic
field only on BLG structure as a channel produces a perfect spin polarization
in a large energy region. Moreover, the conductance could be strongly modulated
by magnetization of the zigzag edge of AB-stacked BLG, and the junction,
entirely made of carbon, produces a giant magnetoresistance (GMR) up to
$10^6\%$. Intestinally, GMR and spin polarization could be tuned by varying BLG
width and length. Generally, MR in a AB-stacked BLG strongly increases
(decreases) with length (width).

###Terahertz frequency spectrum analysis with a nanoscale antiferromagnetic tunnel junction|P. Yu. Artemchuk,O. R. Sulymenko,S. Louis,J. Li,R. Khymyn,E. Bankowski,T. Meitzler,V. S. Tyberkevych,A. N. Slavin,O. V. Prokopenko###

Terahertz frequency spectrum analysis with a nanoscale antiferromagnetic tunnel junction. A method to perform spectrum analysis on low power signals between 0.1 and 10
THz is proposed. It utilizes a nanoscale antiferromagnetic tunnel junction
(ATJ) that produces an oscillating tunneling anisotropic magnetoresistance,
whose frequency is dependent on the magnitude of an evanescent spin current. It
is first shown that the ATJ oscillation frequency can be tuned linearly with
time. Then, it is shown that the ATJ output is highly dependent on matching
conditions that are highly dependent on the dimensions of the dielectric
tunneling barrier. Spectrum analysis can be performed by using an appropriately
designed ATJ, whose frequency is driven to increase linearly with time, a low
pass filter, and a matched filter. This method of THz spectrum analysis, if
realized in experiment, will allow miniaturized electronics to rapidly analyze
low power signals with a simple algorithm. It is also found by simulation and
analytical theory that for an ATJ with a 0.09 $\mu$m$^2$ footprint, spectrum
analysis can be performed over a 0.25 THz bandwidth in just 25 ns on signals
that are at the Johnson-Nyquist thermal noise floor.

###Spin superfluid Josephson oscillator|Yizhou Liu,Igor Barsukov,Ilya Krivorotov,Yafis Barlas,Roger K. Lake###

Spin superfluid Josephson oscillator. The magnetic analogue of the Josephson effect can be exploited to develop a
new class of nano-spin oscillators that we denote as spin superfluid Josephson
oscillators. Such a device, consisting of two exchange coupled easy-plane
metallic ferromagnets separated by a thin normal metal spacer, is proposed and
analyzed. A spin chemical potential difference drives a $2\pi$ precession of
the in-plane magnetization of each ferromagnet. The $2 \pi$ precession angle
gives maximum values of the giant magnetoresistance, resulting in large output
power compared to conventional spin Hall oscillators. An applied ac current
results in a time-averaged magnetoresistance with Shapiro-like steps. The
multistate mode-locking behavior exhibited by the spin Shapiro steps may be
explored for applications in neuromorphic computing. As an experimental
characterization method, electrical measurements of spin superfluid Josephson
junctions can provide additional signatures of spin superfluidity.

###Finite field transport response of a dilute magnetic topological insulator based Josephson junction|Pankaj Mandal,Nicolai Taufertshöfer,Lukas Lunczer,Martin P. Stehno,Charles Gould,Laurens W. Molenkamp###

Finite field transport response of a dilute magnetic topological insulator based Josephson junction. Hybrid samples combining superconductors with magnetic topological insulators
are a promising platform for exploring exotic new transport physics. We examine
a Josephson junction of such a system, based on the dilute magnetic topological
insulator (Hg,Mn)Te and the type II superconductor MoRe. In the zero and very
low field limit, to the best of our knowledge, the device shows, for the first
time, induced supercurrent through a magnetically doped semiconductor, in this
case a topological insulator. At higher fields, a rich and hysteretic
magnetoresistance is revealed. Careful analysis shows that the explanation of
this behaviour can be found in magnetic flux focusing stemming from the
Meissner effect in the superconductor, without invoking any role of proximity
induced superconductivity. The phenomena is important, as it will ubiquitously
co-exist with any exotic new physics that may be present in this class of
devices.

###Andreev Reflection in Ferromagnet/Superconductor/Ferromagnet Double Junction Systems|Taro Yamashita,Hiroshi Imamura,Saburo Takahashi,Sadamichi Maekawa###

Andreev Reflection in Ferromagnet/Superconductor/Ferromagnet Double Junction Systems. We present a theory of Andreev reflection in a
ferromagnet/superconductor/ferromagnet double junction system. The spin
polarized quasiparticles penetrate to the superconductor in the range of
penetration depth from the interface by the Andreev reflection. When the
thickness of the superconductor is comparable to or smaller than the
penetration depth, the spin polarized quasiparticles pass through the
superconductor and therefore the electric current depends on the relative
orientation of magnetizations of the ferromagnets. The dependences of the
magnetoresistance on the thickness of the superconductor, temperature, the
exchange field of the ferromagnets and the height of the interfacial barriers
are analyzed. Our theory explains recent experimental results well.

###Effect of Impurities and Effective Masses on Spin-Dependent Electrical Transport in Ferromagnet-Normal Metal-Ferromagnet Hybrid Junctions|Zhen-Gang Zhu,Gang Su,Biao Jin,Qing-Rong Zheng###

Effect of Impurities and Effective Masses on Spin-Dependent Electrical Transport in Ferromagnet-Normal Metal-Ferromagnet Hybrid Junctions. The effect of nonmagnetic impurities and the effective masses on the
spin-dependent transport in a ferromagnet-normal metal-ferromagnet junction is
investigated on the basis of a two-band model. Our results show that impurities
and the effective masses of electrons in two ferromagnetic electrodes have
remarkable effects on the behaviors of the conductance, namely, both affect the
oscillating amplitudes, periods, as well as the positions of the resonant peaks
of the conductance considerably. The impurity tends to suppress the amplitudes
of the conductance, and makes the spin-valve effect less obvious, but under
certain conditions the phenomenon of the so-called impurity-induced resonant
tunneling is clearly observed. The impurity and the effective mass both can
lead to nonmonotonous oscillation of the junction magnetoresistance (JMR) with
the incident energy and the thickness of the normal metal. It is also observed
that a smaller difference of the effective masses of electrons in two
ferromagnetic electrodes would give rise to a larger amplitude of the JMR.

###Observation of triplet superconductivity in CoSi$_2$/TiSi$_2$ heterostructures|Shao-Pin Chiu,C. C. Tsuei,Sheng-Shiuan Yeh,Fu-Chun Zhang,Stefan Kirchner,Juhn-Jong Lin###

Observation of triplet superconductivity in CoSi$_2$/TiSi$_2$ heterostructures. Unconventional superconductivity and in particular triplet superconductivity
have been front and center of topological materials and quantum technology
research. Here we report our observation of triplet superconductivity in
nonmagnetic CoSi$_2$/TiSi$_2$ heterostructures on silicon. CoSi$_2$ undergoes a
sharp superconducting transition at a critical temperature $T_c \approx$ 1.5 K,
while TiSi$_2$ is a normal metal. We investigate conductance spectra of both
two-terminal CoSi$_2$/TiSi$_2$ tunnel junctions and three-terminal T-shaped
CoSi$_2$/TiSi$_2$ superconducting proximity structures. We report an
unexpectedly large spin-orbit coupling in CoSi$_2$ heterostructures. Below
$T_c$, we observe (1) a narrow zero-bias conductance peak on top of a broad
hump, accompanied by two symmetric side dips in the tunnel junctions, (2) a
narrow zero-bias conductance peak in T-shaped structures, and (3) hysteresis in
the junction magnetoresistance. These three independent and complementary
observations are indicative of chiral $p$-wave pairing in CoSi$_2$/TiSi$_2$
heterostructures. This chiral triplet superconductivity and the excellent
fabrication compatibility of CoSi$_2$ and TiSi$_2$ with present-day silicon
integrated-circuit technology facilitate full scalability for potential use in
quantum-computing devices.

###Competing magnetic anisotropies in atomic-scale junctions|Alexander Thiess,Yuriy Mokrousov,Stefan Heinze###

Competing magnetic anisotropies in atomic-scale junctions. Using first-principles calculations, we study the magnetism of 5d
transition-metal atomic junctions including structural relaxations and
spin-orbit coupling. Upon stretching monatomic chains of W, Ir, and Pt
suspended between two leads, we find the development of strong magnetism and
large values of the magnetocrystalline anisotropy energy (MAE) of up to 30 meV
per chain atom. We predict that switches of the easy magnetization axis of the
nanocontacts upon elongation should be observable by ballistic anisotropic
magnetoresistance measurements. Due to the different local symmetry, the
contributions to the MAE of the central chain atoms and chain atoms in the
vicinity of the leads can have opposite signs which reduces the total MAE. We
demonstrate that this effect occurs independent of the chain length or geometry
of the electrodes.

###Spin transfer torque and anisotropic conductance in spin orbit coupled graphene|Morteza Salehi,Razieh Beiranvand,Mohammad Alidoust###

Spin transfer torque and anisotropic conductance in spin orbit coupled graphene. We theoretically study spin-transfer torque (STT) in a graphene system with
spin-orbit coupling (SOC). We consider a graphene-based junction where the
spin-orbit coupled region is sandwiched between two ferromagnetic (F) segments.
The magnetization in each ferromagnetic segment can possess arbitrary
orientations. Our results show that the presence of SOC results in
anisotropically modified STT, magnetoresistance, and charge conductance as a
function of relative magnetization misalignment in the F regions. We have found
that within the Klein regime, where particles hit the interfaces
perpendicularly, the spin-polarized Dirac fermions transmit perfectly through
the boundaries of an F-F junction (i.e., with zero reflection), regardless of
the relative magnetization misalignment and exert zero STT. In the presence of
SOC, however, due to band structure modification, a nonzero STT reappears. Our
findings can be exploited for experimentally examining proximity-induced SOC
into a graphene system

###Tunable magnetoresistance in an asymmetrically coupled single molecule junction|Ben Warner,Fadi El Hallak,Henning Prüser,John Sharp,Mats Persson,Andrew J. Fisher,Cyrus F. Hirjibehedin###

Tunable magnetoresistance in an asymmetrically coupled single molecule junction. Phenomena that are highly sensitive to magnetic fields can be exploited in
sensors and non-volatile memories. The scaling of such phenomena down to the
single molecule level may enable novel spintronic devices. Here we report
magnetoresistance in a single molecule junction arising from negative
differential resistance that shifts in a magnetic field at a rate two orders of
magnitude larger than Zeeman shifts. This sensitivity to the magnetic field
produces two voltage-tunable forms of magnetoresistance, which can be selected
via the applied bias. The negative differential resistance is caused by
transient charging of an iron phthalocyanine (FePc) molecule on a single layer
of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages
corresponding to the alignment of sharp resonances in the filled and empty
molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider
effect enhances the apparent voltage shift of the negative differential
resistance with magnetic field, which inherently is on the scale of the Zeeman
energy. These results illustrate the impact that asymmetric coupling to
metallic electrodes can have on transport through molecules, and highlight how
this coupling can be used to develop molecular spintronic applications.

###Asymmetric scattering of Dirac electrons and holes in graphene|Atikur Rahman,Janice Wynn Guikema,Nina Markovic###

Asymmetric scattering of Dirac electrons and holes in graphene. The relativistic nature of Dirac electrons and holes in graphene profoundly
affects the way they interact with impurities. Signatures of the relativistic
behavior have been observed recently in scanning tunneling measurements on
individual impurities, but the conductance measurements in this regime are
typically dominated by electron and hole puddles. Here we present measurements
of quantum interference noise and magnetoresistance in graphene pn junctions.
Unlike the conductance, the quantum interference noise can provide access to
the scattering at the Dirac point:it is sensitive to the motion of a single
impurity, it depends strongly on the fundamental symmetries that describe the
system and it is determined by the phase-coherent phenomena which are not
necessarily obscured by the puddles. The temperature and the carrier density
dependence of resistance fluctuations and magnetoresistance in graphene p-n
junctions at low temperatures suggest that the noise is dominated by the
quantum interference due to scattering on impurities and that the noise minimum
could be used to determine the point where the average carrier density is zero.
At larger carrier densities, the amplitude of the noise depends strongly on the
sign of the impurity charge, reflecting the fact that the electrons and the
holes are scattered by the impurity potential in an asymmetric manner.

###Quantum transport modeling of Fe/MgO/Fe magnetic tunnel junction with FeO$_{0.5}$ buffer layer: the effects of correlations|Vladimir Timoshevskii,Yibin Hu,É. Marcotte,Hong Guo###

Quantum transport modeling of Fe/MgO/Fe magnetic tunnel junction with FeO$_{0.5}$ buffer layer: the effects of correlations. We report \textit{ab initio} simulations of quantum transport properties of
Fe/MgO/Fe trilayer structures with FeO$_{0.5}$ buffer iron oxide layer, where
on-site Coulomb interaction is explicitly taken into account by local density
approximation + Hubbard \textit{U} approach. We show that on-site Coulomb
repulsion in the iron-oxygen layer can cause a dramatic drop of the tunnel
magnetoresistance of the system. We present an understanding of microscopic
details of this phenomenon, connecting it to localization of the Fermi
electrons of particular symmetry, which takes place in the buffer Fe-O layer,
when on-site Coulomb repulsion is introduced. We further study the possible
influence of the symmetry reduction in the buffer Fe-O layer on the transport
properties of the Fe/MgO/Fe interface.

###Superconductor-Insulator Magneto-Oscillations in Superconducting Strips|Yeshayahu Atzmon,Efrat Shimshoni###

Superconductor-Insulator Magneto-Oscillations in Superconducting Strips. The magnetoresistance of thin superconducting strips subject to a
perpendicular magnetic field B and low temperatures T manifests a sequence of
alternating superconductor-insulator transitions (SIT). We study this
phenomenon within a quasi one-dimensional (1D) model for the quantum dynamics
of vortices in a line-junction between coupled parallel SC wires, at parameters
close to their SIT. Mapping the vortex system to 1D Fermions at a chemical
potential dictated by B, we find that a quantum phase transition of the Ising
type occurs at critical values of the vortex filling, from a SC phase near
integer filling to an insulator near 1/2-filling. For T->0, the resulting
magnetoresistance R(B) exhibits oscillations similar to the experimental
observation.

###Large magnetoresistance from long-range interface coupling in armchair graphene nanoribbon junctions|Suchun Li,Young-Woo Son,Su Ying Quek###

Large magnetoresistance from long-range interface coupling in armchair graphene nanoribbon junctions. In recent years, bottom-up synthesis procedures have achieved significant
advancements in atomically-controlled growth of several-nanometer-long graphene
nanoribbons with armchair-shaped edges (AGNRs). This greatly encourages us to
explore the potential of such well-defined AGNRs in electronics and
spintronics. Here, we propose an AGNR based spin valve architecture that
induces a large magnetoresistance up to 900%. We find that, when an AGNR is
connected perpendicularly to zigzag-shaped edges, the AGNR allows for
long-range extension of the otherwise localized edge state. The huge
magnetoresistance is a direct consequence of the coupling of two such extended
states from both ends of the AGNR, which forms a perfect transmission channel.
By tuning the coupling between these two spin-polarized states with a magnetic
field, the channel can be destroyed, leading to an abrupt drop in electron
transmission.

###An analytically solvable model of the effect of magnetic breakdown on angle-dependent magnetoresistance in a quasi-two-dimensional metal|Andrzej Nowojewski,Paul A. Goddard,Stephen J. Blundell###

An analytically solvable model of the effect of magnetic breakdown on angle-dependent magnetoresistance in a quasi-two-dimensional metal. We have developed an analytical model of angle-dependent magnetoresistance
oscillations (AMROs) in a quasi-two-dimensional metal in which magnetic
breakdown occurs. The model takes account of all the contributions from
quasiparticles undergoing both magnetic breakdown and Bragg reflection at each
junction and allows extremely efficient simulation of data which can be
compared with recent experimental results on the organic metal
kappa-ET2Cu(NCS)2. AMROs resulting from both closed and open orbits emerge
naturally at low field, and the model enables the transition to breakdown-AMROs
with increasing field to be described in detail.

###Magnetoresistance of Junctions made of Underdoped YBCO Separated by a Ga-doped YBCO Barrier|L. Shkedy,G. Koren,E. Polturak###

Magnetoresistance of Junctions made of Underdoped YBCO Separated by a Ga-doped YBCO Barrier. We report magnetoresistance measurements of ramp type
superconductor-normal-superconductor (SNS) junctions. The junctions consist of
underdoped $YBa_{2}Cu_{3}O_y$ (YBCO) electrodes separated by a barrier of
$YBa_{2}Cu_{2.6}Ga_{0.4}O_y$. We observe a large positive magnetoresistance,
linear in the field. We suggest that this unusual magnetoresistance originates
in the field dependence of the proximity effect. Our results indicate that in
underdoped YBCO/N/YBCO SNS structures, the proximity effect does not exhibit
the anomalously long range found in optimally doped YBCO structures. From our
data we obtain the diffusion coefficient and relaxation time of quasiparticles
in underdoped YBCO.

###Controllable generation of a spin-triplet supercurrent in a Josephson spin-valve|Adrian Iovan,Taras Golod,Vladimir M. Krasnov###

Controllable generation of a spin-triplet supercurrent in a Josephson spin-valve. It has been predicted theoretically that an unconventional odd-frequency
spin-triplet component of superconducting order parameter can be induced in
multilayered ferromagnetic structures with non-collinear magnetization. In this
work we study experimentally nano-scale devices, in which a ferromagnetic spin
valve is embedded into a Josephson junction. We demonstrate two ways of in-situ
analysis of such Josephson spin valves: via magnetoresistance measurements and
via in-situ magnetometry based on flux quantization in the junction. We observe
that supercurrent through the device depends on the relative orientation of
magnetization of the two ferromagnetic layers and is enhanced in the
non-collinear state of the spin valve. This provides a direct prove of
controllable generation of the spin-triplet superconducting component in a
ferromagnet.

###Spin transport in Si-based spin metal-oxide-semiconductor field-effect transistors: Spin drift effect in the inversion channel and spin relaxation in the n+-Si source/drain regions|Shoichi Sato,Masaaki Tanaka,Ryosho Nakane###

Spin transport in Si-based spin metal-oxide-semiconductor field-effect transistors: Spin drift effect in the inversion channel and spin relaxation in the n+-Si source/drain regions. We have experimentally and theoretically investigated the electron spin
transport and spin distribution at room temperature in a Si two-dimensional
(2D) inversion channel of back-gate-type spin metal-oxide-semiconductor
field-effect transistors (spin MOSFETs). The magnetoresistance ratio of the
spin MOSFET with a channel length of 0.4$\mu$m was increased by a factor of 6
from that in our previous paper [Phys. Rev. B 99, 165301 (2019)] by lowering
the parasitic resistances at the source/drain junctions with
highly-phosphorus-doped n+-Si regions and by increasing the lateral electric
field in the channel along the electron transport, called "spin drift". Clear
Hanle signals with some oscillation peaks were observed for the spin MOSFET
with a channel length of 10 $\mu$ m under the lateral electric field,
indicating that the effective spin diffusion length is dramatically enhanced by
the spin drift. By taking into account the n+-Si regions and the spin drift in
the channel, one-dimensional analytic functions were derived for analyzing the
effect of the spin drift on the spin transport through the channel and these
functions were found to explain almost all the experimental results. From the
calculated spin current and spin distribution, it was revealed that almost all
the spins are unflipped during the spin-drift-assisted transport through the
0.4-$\mu$m-long inversion channel, but the most part of the injected spins from
the source electrode are relaxed in the n+-Si regions of both the source and
drain junctions. This means that the spin drift is useful and precise design of
the device structure is essential to obtain a higher magnetoresistance ratio.
Furthermore, we showed that the effective spin resistances that are introduced
in this study are very helpful to understand how to improve the
magnetoresistance ratio of spin MOSFETs for practical use.

###Laser-assisted spin-polarized transport in graphene tunnel junctions|Kai-He Ding,Zhen-Gang Zhu,Jamal Berakdar###

Laser-assisted spin-polarized transport in graphene tunnel junctions. Keldysh nonequilibrium Green's function method is utilized to study
theoretically the spin polarized transport through a graphene spin valve
irradiated by a monochromatic laser field. It is found that the bias dependence
of the differential conductance exhibits successive peaks corresponding to the
resonant tunneling through the photon-assisted sidebands. The multi photon
processes originate from the combined effects of the radiation field and the
graphene tunneling properties, and are shown to be substantially suppressed in
a graphene spin valve which results in a decrease of the differential
conductance for a high bias voltage. We also discussed the appearance of a
dynamical gap around zero bias due to the radiation field. The gap width can be
tuned by changing the radiation electric field strength and the frequency. This
leads to a shift of the resonant peaks in the differential conductance. We also
demonstrate numerically the dependencies of the radiation and spin valve
effects on the parameters of the external fields and those of the electrodes.
We find that the combined effects of the radiation field, the graphene, and the
spin valve properties bring about an oscillatory behavior in the tunnel
magnetoresistance (TMR), and this oscillatory amplitude can be changed by
scanning the radiation field strength and/or the frequency.

###Interface bonding of a ferromagnetic/semiconductor junction : a photoemission study of Fe/ZnSe(001)|M. Eddrief,M. Marangolo,V. H. Etgens,S. Ustaze,F. Sirotti,M. Mulazzi,G. Panaccione,D. H. Mosca,B. Lepine,P. Schieffer###

Interface bonding of a ferromagnetic/semiconductor junction : a photoemission study of Fe/ZnSe(001). We have probed the interface of a ferromagnetic/semiconductor (FM/SC)
heterojunction by a combined high resolution photoemission spectroscopy and
x-ray photoelectron diffraction study. Fe/ZnSe(001) is considered as an example
of a very low reactivity interface system and it expected to constitute large
Tunnel Magnetoresistance devices. We focus on the interface atomic environment,
on the microscopic processes of the interface formation and on the iron
valence-band. We show that the Fe contact with ZnSe induces a chemical
conversion of the ZnSe outermost atomic layers. The main driving force that
induces this rearrangement is the requirement for a stable Fe-Se bonding at the
interface and a Se monolayer that floats at the Fe growth front. The released
Zn atoms are incorporated in substitution in the Fe lattice position. This
formation process is independent of the ZnSe surface termination (Zn or Se).
The Fe valence-band evolution indicates that the d-states at the Fermi level
show up even at submonolayer Fe coverage but that the Fe bulk character is only
recovered above 10 monolayers. Indeed, the Fe &#61508;1-band states,
theoretically predicted to dominate the tunneling conductance of Fe/ZnSe/Fe
junctions, are strongly modified at the FM/SC interface.

###Spin-orbit torques from interfacial spin-orbit coupling for various interfaces|Kyoung-Whan Kim,Kyung-Jin Lee,Jairo Sinova,Hyun-Woo Lee,M. D. Stiles###

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces. We use a perturbative approach to study the effects of interfacial spin-orbit
coupling in magnetic multilayers by treating the two-dimensional Rashba model
in a fully three-dimensional description of electron transport near an
interface. This formalism provides a compact analytic expression for
current-induced spin-orbit torques in terms of unperturbed scattering
coefficients, allowing computation of spin-orbit torques for various contexts,
by simply substituting scattering coefficients into the formulas. It applies to
calculations of spin-orbit torques for magnetic bilayers with bulk magnetism,
those with interface magnetism, a normal metal/ferromagnetic insulator
junction, and a topological insulator/ferromagnet junction. It predicts a
dampinglike component of spin-orbit torque that is distinct from any intrinsic
contribution or those that arise from particular spin relaxation mechanisms. We
discuss the effects of proximity-induced magnetism and insertion of an
additional layer and provide formulas for in-plane current, which is induced by
a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in
the same formalism.

###Magnetoresistance and negative differential resistance in Ni/Graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study|Kamal K. Saha,Anders Blom,Kristian S. Thygesen,Branislav K. Nikolic###

Magnetoresistance and negative differential resistance in Ni/Graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study. Using the nonequilibrium Green function formalism combined with density
functional theory, we study finite-bias quantum transport in Ni/Gr_n/Ni
vertical heterostructures where $n$ graphene layers are sandwiched between two
semi-infinite Ni(111) electrodes. We find that recently predicted "pessimistic"
magnetoresistance of 100% for $n \ge 5$ junctions at zero bias voltage $V_b
\rightarrow 0$, persists up to $V_b \simeq 0.4$ V, which makes such devices
promising for spin-torque-based device applications. In addition, for parallel
orientations of the Ni magnetizations, the $n=5$ junction exhibits a pronounced
negative differential resistance as the bias voltage is increased from $V_b=0$
V to $V_b \simeq 0.5$ V. We confirm that both of these nonequilibrium effects
hold for different types of bonding of Gr on the Ni(111) surface while
maintaining Bernal stacking between individual Gr layers.

###Observation of the dominant spin-triplet supercurrent in Josephson spin valves with strong Ni ferromagnets|O. M. Kapran,A. Iovan,T. Golod,V. M. Krasnov###

Observation of the dominant spin-triplet supercurrent in Josephson spin valves with strong Ni ferromagnets. We study experimentally nanoscale Josephson junctions and Josephson
spin-valves containing strong Ni ferromagnets. We observe that in contrast to
junctions, spin valves with the same geometry exhibit anomalous Ic(H) patterns
with two peaks separated by a dip. We develop several techniques for in-situ
characterization of micromagnetic states in our nano-devices, including
magnetoresistance, absolute Josephson fluxometry and
First-Order-Reversal-Curves analysis. They reveal a clear correlation of the
dip in supercurrent with the antiparallel state of a spin-valve and the peaks
with two noncollinear magnetic states, thus providing evidence for generation
of spin-triplet superconductivity. A quantitative analysis brings us to a
conclusion that the triplet current in out Ni-based spin-valves is
approximately three times larger than the conventional singlet supercurrent.

###Ballistic Spin Injection and Detection in Fe/Semiconductor/Fe Junctions|Phivos Mavropoulos,Olaf Wunnicke,Peter H. Dederichs###

Ballistic Spin Injection and Detection in Fe/Semiconductor/Fe Junctions. We present {\it ab initio} calculations of the spin-dependent electronic
transport in Fe/GaAs/Fe and Fe/ZnSe/Fe (001) junctions simulating the situation
of a spin-injection experiment. We follow a ballistic Landauer-B\"uttiker
approach for the calculation of the spin-dependent dc conductance in the
linear-responce regime, in the limit of zero temperature. We show that the bulk
band structure of the leads and of the semiconductor, and even more the
electronic structure of a clean and abrupt interface, are responsible for a
current polarisation and a magnetoresistance ratio of almost the ideal 100%, if
the transport is ballistic. In particular we study the significance of the
transmission resonances caused by the presence of two interfaces.

###All-Heusler giant-magnetoresistance junctions with matched energy bands and Fermi surfaces|Zhaoqiang Bai,Yongqing Cai,Lei Shen,Guchang Han,Yuanping Feng###

All-Heusler giant-magnetoresistance junctions with matched energy bands and Fermi surfaces. We present an all-Heusler architecture which could be used as a rational
design scheme for achieving high spin-filtering efficiency in the
current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A
Co2MnSi/Ni2NiSi/Co2MnSi trilayer stack is chosen as the prototype of such an
architecture, of which the electronic structure and magnetotransport properties
are systematically investigated by first principles approaches. Almost
perfectly matched energy bands and Fermi surfaces between the all-Heusler
electrode-spacer pair are found, indicating large interfacial spin-asymmetry,
high spin-injection efficiency, and consequently high GMR ratio. Transport
calculations further confirms the superiority of the all-Heusler architecture
over the conventional Heusler/transition-metal(TM) structure by comparing their
transmission coefficients and interfacial resistances of parallel conduction
electrons, as well as the macroscopic current-voltage (I-V) characteristics. We
suggest future theoretical and experimental efforts in developing novel
all-Heusler GMR junctions for the read heads of the next generation
high-density hard disk drives (HDDs).

###Robustness of the magnetoresistance of nanoparticle arrays|V. Estevez,E. Bascones###

Robustness of the magnetoresistance of nanoparticle arrays. Recent work has found that the interplay between spin accumulation and
Coulomb blockade in nanoparticle arrays results in peaky I-V and tunneling
magnetoresistance (TMR) curves and in huge values of the TMR. We analyze how
these effects are influenced by a polarization asymmetry of the electrodes, the
dimensionality of the array, the temperature, resistance or charge disorder and
long-range interactions. We show that the magnitude and voltage dependence of
the TMR does not change with the dimensionality of the array or the presence of
junction resistance disorder. A different polarization in the electrodes
modifies the peak shape in the I-V and TMR curves but not their order of
magnitude. Increasing the temperature or length of the interaction reduces to
some extent the size of the peaks, being the reduction due to long-range
interactions smaller in longer arrays. Charge disorder should be avoided to
observe large TMR values.

###Interfacial Spin-Orbit Coupling: New Platform for Superconducting Spintronics|Isidoro Martínez,Petra Högl,César González-Ruano,Juan Pedro Cascales,Coriolan Tiusan,Yuan Lu,Michel Hehn,Alex Matos-Abiague,Jaroslav Fabian,Igor Žutić,Farkhad G. Aliev###

Interfacial Spin-Orbit Coupling: New Platform for Superconducting Spintronics. Spin-orbit coupling (SOC) is a key interaction in spintronics, allowing an
electrical control of spin or magnetization and, vice versa, a magnetic control
of electrical current. However, recent advances have revealed much broader
implications of SOC that is also central to the design of topological states,
including topological insulators, skyrmions, and Majorana fermions, or to
overcome the exclusion of two-dimensional ferro-magnetism expected from the
Mermin-Wagner theorem. SOC and the resulting emergent interfacial spin-orbit
fields are simply realized in junctions through structural inversion asymmetry,
while the anisotropy in magnetoresistance (MR) allows for their experimental
detection. Surprisingly, we demonstrate that an all-epitaxial
ferromagnet/MgO/metal junction with only a negligible MR anisotropy undergoes a
remarkable transformation below the superconducting transition temperature of
the metal. The superconducting junction has a three orders of magnitude higher
MR anisotropy and supports the formation of spin-triplet superconductivity,
crucial for superconducting spintronics, and topologically-protected quantum
computing. Our findings call for revisiting the role of SOC in other systems
which, even when it seems negligible in the normal state, could have a profound
influence on the superconducting response.

###Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by charge transfer and proximity-induced spin splitting in graphene|P. U. Asshoff,J. L. Sambricio,A. P. Rooney,S. Slizovskiy,A. Mishchenko,A. M. Rakowski,E. W. Hill,A. K. Geim,S. J. Haigh,V. I. Fal'ko,I. J. Vera-Marun,I. V. Grigorieva###

Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by charge transfer and proximity-induced spin splitting in graphene. Graphene is hailed as an ideal material for spintronics due to weak intrinsic
spin-orbit interaction that facilitates lateral spin transport and tunability
of its electronic properties, including a possibility to induce magnetism in
graphene. Another promising application of graphene is related to its use as a
spacer separating ferromagnetic metals (FMs) in vertical magnetoresistive
devices, the most prominent class of spintronic devices widely used as magnetic
sensors. In particular, few-layer graphene was predicted to act as a perfect
spin filter. Here we show that the role of graphene in such devices (at least
in the absence of epitaxial alignment between graphene and the FMs) is
different and determined by proximity-induced spin splitting and charge
transfer with adjacent ferromagnetic metals, making graphene a weak FM
electrode rather than a spin filter. To this end, we report observations of
magnetoresistance (MR) in vertical Co-graphene-NiFe junctions with 1 to 4
graphene layers separating the ferromagnets, and demonstrate that the
dependence of the MR sign on the number of layers and its inversion at
relatively small bias voltages is consistent with spin transport between weakly
doped and differently spin-polarized layers of graphene. The proposed
interpretation is supported by the observation of an MR sign reversal in biased
Co-graphene-hBN-NiFe devices and by comprehensive structural characterization.
Our results suggest a new architecture for vertical devices with electrically
controlled MR.

###Effect of charge ordering on the electrical properties and magnetoresistance of manganites|Mahrous R. Ahmed###

Effect of charge ordering on the electrical properties and magnetoresistance of manganites. The Monte Carlo Ferromagnetic Ising model was used to study the electrical
properties of manganese oxides due to the charge ordering phase occurring at
doping, x = 0.5. The half-doped manganites have an insulator antiferromagnetic
ground state. We calculated the internal energy, specific heat, resistivity and
the magneto-resistance, MR, with parallel and anti-parallel applied magnetic
fields. Our simulation reveals that the resistivity decreases exponentially and
the electric current increases with increasing temperature according the free
charge increase, to transport from an insulator to conductor phase. The
magnetoresistance has negative small values with parallel magnetic field but
has positive high values with unti-parallel magnetic field. The obtained
semiconductor-metal transition behavior candidates the half-doped manganites to
be very good semiconductors diode junctions.

###Selective transmission of Dirac electrons and ballistic magnetoresistance of \textit{n-p} junctions in graphene|Vadim V. Cheianov,Vladimir I. Fal'ko###

Selective transmission of Dirac electrons and ballistic magnetoresistance of \textit{n-p} junctions in graphene. We show that an electrostatically created n-p junction separating the
electron and hole gas regions in a graphene monolayer transmits only those
quasiparticles that approach it almost perpendicularly to the n-p interface.
Such a selective transmission of carriers by a single n-p junction would
manifest itself in non-local magnetoresistance effect in arrays of such
junctions and determines the unusual Fano factor in the current noise universal
for the n-p junctions in graphene.

###Spintronics of metal ferromagnetic structures: New approaches in the theory and experiments|S. G. Chigarev,E. M. Epshtein,Yu. V. Gulyaev,P. E. Zilberman###

Spintronics of metal ferromagnetic structures: New approaches in the theory and experiments. Two channels of the sd exchange interaction are considered in magnetic
junctions. The first channel describes the interaction of transversal spins
with the lattice magnetization. The second one describes the interaction of
longitudinal spins with magnetization. We show the longitudinal channel leads
to a number of significant effects: 1) drastic lowering of the current
instability threshold down to three (or even more) orders of magnitude; 2)
creation of large enough distortion of equilibrium due to current driven spin
injection leading to inversion of energy spin subband populations and
laser-like instability in THz frequency range at room temperature. External
magnetic field may tend to lower additionally the instability threshold due to
the proximity effect of purely magnetic reorientation phase transition. This
effect demonstrates the new properties: the giant magnetoresistance (GMR)
becomes strongly current dependent and the exchange switching becomes of very
low threshold. We derived some matching condition that should be satisfied to
achieve high spin injection level. Some characteristic quantities were appeared
in the condition. We investigated also the junctions having variable lateral
dimensions of the layers, for example, a ferromagnetic rod contacting with a
very thin ferromagnetic film. Large enhancement of the current density may
appear near the contact region leading to the spin injection luminescence.

###Magnon-mediated interlayer coupling in an all-antiferromagnetic junction|Yongjian Zhou,Liyang Liao,Xiaofeng Zhou,Hua Bai,Mingkun Zhao,Caihua Wan,Siqi Yin,Lin Huang,Tingwen Guo,Lei Han,Ruyi Chen,Zhiyuan Zhou,Xiufeng Han,Feng Pan,Cheng Song###

Magnon-mediated interlayer coupling in an all-antiferromagnetic junction. The interlayer coupling mediated by fermions in ferromagnets brings about
parallel and anti-parallel magnetization orientations of two magnetic layers,
resulting in the giant magnetoresistance, which forms the foundation in
spintronics and accelerates the development of information technology. However,
the interlayer coupling mediated by another kind of quasi-particle, boson, is
still lacking. Here we demonstrate such a static interlayer coupling at room
temperature in an antiferromagnetic junction Fe2O3/Cr2O3/Fe2O3, where the two
antiferromagnetic Fe2O3 layers are functional materials and the
antiferromagnetic Cr2O3 layer serves as a spacer. The N\'eel vectors in the top
and bottom Fe2O3 are strongly orthogonally coupled, which is bridged by a
typical bosonic excitation (magnon) in the Cr2O3 spacer. Such an orthogonally
coupling exceeds the category of traditional collinear interlayer coupling via
fermions in ground state, reflecting the fluctuating nature of the magnons, as
supported by our magnon quantum well model. Besides the fundamental
significance on the quasi-particle-mediated interaction, the strong coupling in
an antiferromagnetic magnon junction makes it a realistic candidate for
practical antiferromagnetic spintronics and magnonics with ultrahigh-density
integration.

###Andreev reflection and strongly enhanced magnetoresistance oscillations in GaInAs/InP heterostructures with superconducting contacts|I. E. Batov,Th. Schapers,N. M. Chtchelkatchev,H. Hardtdegen,A. V. Ustinov###

Andreev reflection and strongly enhanced magnetoresistance oscillations in GaInAs/InP heterostructures with superconducting contacts. We study the magnetotransport in small hybrid junctions formed by
high-mobility GaInAs/InP heterostructures coupled to superconducting (S) and
normal metal (N) terminals. Highly transmissive superconducting contacts to a
two-dimensional electron gas (2DEG) located in a GaInAs/InP heterostructure are
realized by using a Au/NbN layer system. The magnetoresistance of the S/2DEG/N
structures is studied as a function of dc bias current and temperature. At bias
currents below a critical value, the resistance of the S/2DEG/N structures
develops a strong oscillatory dependence on the magnetic field, with an
amplitude of the oscillations considerably larger than that of the reference
N/2DEG/N structures. The experimental results are qualitatively explained by
taking Andreev reflection in high magnetic fields into account.

###Metal-terminated Graphene Nanoribbons|Yan Wang,Chao Cao,Hai-Ping Cheng###

Metal-terminated Graphene Nanoribbons. We have investigated structure, electronic, and magnetic properties of
metal-terminated zigzag graphene nanoribbons (M-ZGNRs) by first-principles
calculations. Two families of metal terminations are studied: (1) 3d-transition
metals (TMs) Fe, Co, and Ni and (2) noble metals (NMs) Cu, Ag, and Au. All
systems have spin-polarized edge states with antiferromagnetic (AFM) ordering
between two edges, except Co-ZGNRs and Ni-ZGNRs which exhibit negligibly small
energy differences between AFM and ferromagnetic states with the given ribbon
width. In the AFM state the TM terminations transform semiconducting ZGNRs into
metallic ones while the band gap remains in ZGNR with NM terminations.
Ferromagnetic states of M-ZGNRs with TM terminations show a high degree of spin
polarization at the Fermi energy. We predict a large magnetoresistance in
Fe-ZGNR junctions with a low, uniform magnetic switching field.

###Non-s wave superconductivity in boron-doped nanodiamond films with 0-π Josephson junction array|Somnath Bhattacharyya,Christopher Coleman,Davie Mtsuko,Dmitri Churochkin###

Non-s wave superconductivity in boron-doped nanodiamond films with 0-π Josephson junction array. Superconducting transport properties of granular materials are greatly
influenced by the microstructure. We show that in heavily boron-doped diamond
films (HBDDF) films some sharp transport features can be manipulated by
applying a magnetic field and controlled finite bias current. We demonstrate
the conductivity cross-over from dirty metal to the superconducting state
through an insulating peak arising at a very low current or magnetic field
region and particularly pronounced negative magnetoresistance with periodic
oscillatory features. The current-voltage characteristics show features of the
Berezinskii-Kosterlitz-Thouless (BKT) phase transitions which verifies the
two-dimensional structure in HBDDF observed recently. A zero bias conductance
peak can be attributed to the Andreev bound state formed at the grain
boundaries of diamond nanocrystals. The set of observations can be
qualitatively explained consistently through the concept of a superconducting
transition with a non-s wave order parameter in the diamond heterostructures.

###Electrical and magnetic properties of nano-scale Pi-junctions|Samanta Piano###

Electrical and magnetic properties of nano-scale Pi-junctions. The physics of the "Pi" phase shift in ferromagnetic Josephson junctions
enables a range of applications for spin-electronic devices and quantum
computing. In this respect our research is devoted to the evaluation of the
best materials for the development and the realization of the quantum devices
based on superconductors and at the same point towards the reduction of the
size of the employed heterostructures towards and below nano-scale. In this
chapter we report our investigation of transitions from "0" to "Pi" states in
Nb Josephson junctions with strongly ferromagnetic barriers of Co, Ni,
Ni$_{80}$Fe$_{20}$ (Py) and Fe. We show that it is possible to fabricate
nanostructured Nb/ Ni(Co, Py, Fe)/Nb $\pi$-junctions with a nano-scale magnetic
dead layer and with a high level of control over the ferromagnetic barrier
thickness variation. In agreement with the theoretical model we estimate, from
the oscillations of the critical current as function of the ferromagnetic
barrier thickness, the exchange energy of the ferromagnetic material and we
obtain that it is close to bulk ferromagnetic materials implying that the
ferromagnet is clean and S/F roughness is minimal. We conclude that S/F/S
Josephson junctions are viable structures in the development of
superconductor-based quantum electronic devices; in particular Nb/Co/Nb and
Nb/Fe/Nb multilayers with their low value of the magnetic dead layer and high
value of the exchange energy can readily be used in controllable two-level
quantum information systems. In this respect, we discuss applications of our
nano-junctions to engineering magnetoresistive devices such as programmable
pseudo-spin-valve Josephson structures.

###Realization of an N-shaped IVC of nanoscale metallic junctions using the antiferromagnetic transition|Yu. G. Naidyuk,K. Gloos,I. K. Yanson###

Realization of an N-shaped IVC of nanoscale metallic junctions using the antiferromagnetic transition. We have observed at low temperatures (<8K) hysteretic I(V) characteristics
for sub-mkm (~200nm) metallic break-junctions based on the heavy-fermion
compound UPd2Al3. Degrading the quality of the contacts by in situ increasing
the local residual resistivity or temperature rise reduces the hysteresis. We
demonstrate that those hysteretic I(V) curves can be reproduced theoretically
by assuming the constriction to be in the thermal regime. Our calculations show
that such anomalous I(V) curves are due to the sharp increase of \rho(T) of
UPd2Al3 near the Neel temperature T_N ~ 14K. From this point of view each metal
with similar \rho(T) should produce similar hysteretic I(V) curves. As example
we show calculations for the rare-earth manganite La{0.75}Sr{0.25}MnO3, a
system with colossal magnetoresistance. In this way we demonstrate that
nano-sized point contacts can be non-linear devices with N-shaped I(V)
characteristics, i. e. with negative differential resistance, that could serve
like Esaki tunnel diodes or Gunn diodes as amplifiers, generators, and
switching units. Their characteristic response time is estimated to be less
than 1ns for the investigated contacts.

###Signature of gate-tunable magnetism in graphene grafted with Pt-porphyrins|Chuan Li,Katsuyoshi Komatsu,G. Clave,S. Campidelli,A. Filoramo,S. Gueron,H. Bouchiat###

Signature of gate-tunable magnetism in graphene grafted with Pt-porphyrins. Inducing magnetism in graphene holds great promises, such as controlling the
exchange interaction with a gate electrode and generating exotic magnetic
phases. Coating graphene with magnetic molecules or atoms has so far mostly
lead to decreased graphene mobility. In the present work, we show that
Pt-porphyrins adsorbed on graphene lead to an enhanced mobility and to
gate-dependent magnetism. We report that porphyrins can be donor or acceptor,
depending on graphene s initial doping. The porphyrins transfer charge and
ionize around the charged impurities on graphene, decreasing the graphene
doping and increasing its mobility. In addition, ionized porphyrins carry a
magnetic moment. Using the sensitivity of mesoscopic transport to magnetism, in
particular the superconducting proximity effect and conductance fluctuations,
we explore the magnetic order induced in graphene by the interacting magnetic
moments of the ionized porphyrins. Among the signatures of magnetism, we find
two-terminal-magnetoresistance fluctuations with an odd component, a tell-tale
sign of time reversal symmetry breaking at zero field, that does not exist in
uncoated graphene sample. When graphene is connected to superconducting
electrodes, the induced magnetism leads to a gate-voltage-dependent suppression
of the supercurrent, modified magnetic interference patterns, and
gate-voltage-dependent magnetic hysteresis. The magnetic signatures are
greatest for long superconductor graphene superconductor junctions and for
samples with the highest initial doping, compatible with a greater number of
ionized and thus magnetic porphyrins. Our findings suggest that long-range
magnetism is induced through graphene by the ionized porphyrins magnetic
moment. This magnetic interaction is controlled by the density of carriers in
graphene, a tunability that could be exploited in spintronic applications.

###Thin-Film Trilayer Manganate Junctions|Jonathan Z. Sun###

Thin-Film Trilayer Manganate Junctions. Spin-dependent conductance across a manganate-barrier-manganate junction has
recently been demonstrated. The junction is a La$_{0.67}$Sr$_{0.33}$MnO$_3$%
-SrTiO$_3$-La$_{0.67}$ Sr$_{0.33}$MnO$_3$ trilayer device supporting
current-perpendicular transport. Large magnetoresistance of up to a factor of
five change was observed in these junctions at 4.2K in a relatively low field
of the order of 100 Oe. Temperature and bias dependent studies revealed a
complex junction interface structure whose materials physics has yet to be
understood.

###Oscillating magnetoresistance in graphene p-n junctions at intermediate magnetic fields|Hiske Overweg,Hannah Eggimann,Ming-Hao Liu,Anastasia Varlet,Marius Eich,Pauline Simonet,Yongjin Lee,Kenji Watanabe,Takashi Taniguchi,Klaus Richter,Vladimir I. Fal'ko,Klaus Ensslin,Thomas Ihn###

Oscillating magnetoresistance in graphene p-n junctions at intermediate magnetic fields. We report on the observation of magnetoresistance oscillations in graphene
p-n junctions. The oscillations have been observed for six samples, consisting
of single-layer and bilayer graphene, and persist up to temperatures of 30 K,
where standard Shubnikov-de Haas oscillations are no longer discernible. The
oscillatory magnetoresistance can be reproduced by tight-binding simulations.
We attribute this phenomenon to the modulated densities of states in the n- and
p- regions.

###Giant orbital moments are responsible for the anisotropic magnetoresistance of atomic contacts|Gabriel Autes,Cyrille Barreteau,Marie-Catherine Desjonquères,Daniel Spanjaard,Michel Viret###

Giant orbital moments are responsible for the anisotropic magnetoresistance of atomic contacts. We study here, both experimentally and theoretically, the anisotropy of
magnetoresistance in atomic contacts. Our measurements on iron break junctions
reveal an abrupt and hysteretic switch between two conductance levels when a
large applied field is continuously rotated. We show that this behaviour stems
from the coexistence of two metastable electronic states which result from the
anisotropy of electronic interactions responsible for the enhancement of
orbital magnetization. In both states giant orbital moments appear on the low
coordinated central atom in a realistic contact geometry. However they differ
by their orientation, parallel or perpendicular, with respect to the axis of
the contact. Our explanation is totally at variance with the usual model based
on the band structure of a monatomic linear chain, which we argue cannot be
applied to 3d ferromagnetic metals.

###Edge proximity-induced magnetoresistance and spin polarization in ferromagnetic gated bilayer graphene nanoribbon|Vahid Derakhshan,Hosein Cheraghchi###

Edge proximity-induced magnetoresistance and spin polarization in ferromagnetic gated bilayer graphene nanoribbon. Coherent spin-dependent transport through a junction containing of
Normal/Ferromagnetic/Normal bilayer graphene nanoribbon with zigzag edges is
investigated by using Landauer formalism. In a more realistic set-up, the
exchange field is induced by two ferromagnetic insulator strips deposited on
the ribbon edges while a perpendicular electric field is applied by the top
gated electrodes. Our results show that, for antiparallel configuration, a band
gap is opened giving rise a semiconducting behavior, while for parallel
configuration, the band structure has no band gap. As a result, a giant
magnetoresistance is achievable by changing the alignment of induced
magnetization. Application of a perpendicular electric field on the parallel
configuration, results in a spin field-effect transistor where a fully spin
polarization occurs around the Dirac point. To be comparable our results with
the one for monolayer graphene, we demonstrate that the reflection symmetry and
so the parity conservation fails in bilayer graphene nanoribbons with the
zigzag edges.

###Electronic transport through a graphene-based ferromagnetic/normal/ferromagnetic junction|Jiang-chai Chen,Shu-guang Cheng,Shun-Qing Shen,Qing-feng Sun###

Electronic transport through a graphene-based ferromagnetic/normal/ferromagnetic junction. Electronic transport in a graphene-based ferromagnetic/normal/ferromagnetic
junction is investigated by means of Landauer-B\"{u}ttiker formulism and the
nonequilibrium Green's function technique. For the zigzag edge case, the
results show that the conductance is always larger than $e^{2}/h$ for the
parallel configuration of lead magnetizations, but for the antiparallel
configuration the conductance becomes zero because of the band-selective rule.
So a magnetoresistance (MR) plateau emerges with the value 100% when the Fermi
energy is located around the Dirac point. Besides, choosing narrower graphene
ribbons can obtain the wider 100% MR plateaus and the length change of the
central graphene region does not affect the 100% MR plateaus. Although the
disorder will reduce the MR plateau, the plateau value can be still kept about
50% even in a large disorder strength case. In addition, when the
magnetizations of the left and right leads have a relative angle, the
conductance changes as a cosine function of the angle. What is more, for the
armchair edge case, the MR is usually small. So, it is more favorable to
fabricate the graphene-based spin valve device by using the zigzag edge
graphene ribbon.

###Ballistic transport in ferromagnet-superconductor-ferromagnet trilayers with arbitrary orientation of magnetizations|Milos Bozovic,Zoran Radovic###

Ballistic transport in ferromagnet-superconductor-ferromagnet trilayers with arbitrary orientation of magnetizations. Transport phenomena in clean ferromagnet-superconductor-ferromagnet (FSF)
trilayers are studied theoretically for a general case of arbitrary orientation
of in-plane magnetizations and interface transparencies. Generalized
expressions for scattering probabilities are derived and the differential
conductance is computed using solutions of the Bogoliubov-de Gennes equation.
We focus on size and coherence effects that characterize ballistic transport,
in particular on the subgap transmission and geometrical oscillations of the
conductance. We find a monotonic dependence of conductance spectra and
magnetoresistance on the angle of misorientation of magnetizations as their
alignment is changed from parallel to antiparallel. Spin-triplet pair
correlations in FSF heterostructures induced by non-collinearity of
magnetizations are investigated by solving the Gor'kov equations in the clean
limit. Unlike diffusive FSF junctions, where the triplet correlations have a
long-range monotonic decay, we show that in clean ferromagnet-superconductor
hybrids both singlet and triplet pair correlations induced in the F layers are
oscillating and power-law decaying with the distance from the S-F interfaces.

###Implementation of a non-equilibrium Green's function method to calculate spin transfer torque|Christian Heiliger,Michael Czerner,Bogdan Yu. Yavorsky,Ingrid Mertig,Mark D. Stiles###

Implementation of a non-equilibrium Green's function method to calculate spin transfer torque. We present an implementation of the steady state Keldysh approach in a
Green's function multiple scattering scheme to calculate the non-equilibrium
spin density. This density is used to obtain the spin transfer torque in
junctions showing the magnetoresistance effect. We use our implementation to
study the spin transfer torque in metallic Co/Cu/Co junctions.

###Lower critical field and intragrain critical current density in the ruthenate-cuprate RuSr$_{2}$Gd$_{1.5}$Ce$_{0.5}$Cu$_{2}$O$_{10}$|M. G. das Virgens,S. García,L. Ghivelder###

Lower critical field and intragrain critical current density in the ruthenate-cuprate RuSr$_{2}$Gd$_{1.5}$Ce$_{0.5}$Cu$_{2}$O$_{10}$. The lower critical field of the grains, $H_{c1}$, and the intragrain critical
current density, $J_{c}$, were determined for the superconducting
ruthenate-cuprate RuSr$_{2}$Gd$_{1.5}$Ce$_{0.5}$Cu$_{2}$O$_{10-\delta}$
[Ru-1222(Gd)] through a systematic study of the hysteresis in magnetoresistance
loops. A reliable method, based on the effects of the magnetization of the
grains on the net local field at the intergranular junctions is provided,
circumventing the problem of the strong masking of the superconducting
diamagnetic signal by the ferromagnetic background. The temperature dependency
of $H_{c1}$ and $J_{c}$ both exhibit a smooth increase on cooling without
saturation down to $T/T_{SC}$ $\cong $ 0.2. The obtained $H_{c1}$ values vary
between 150 and 1500 Oe in the 0.2 $\leq $ $% T/T_{SC}$ $\leq $ 0.4 interval,
for samples annealed in an oxygen flow; oxygenation under high pressure (50
atm) leads to a further increase. These values are much larger than the
previously reported rough assessments (25-50 Oe), using conventional
magnetization measurements. High $J_{c}$ values of $% \sim $ 10$^{7}$
A/cm$^{2}$, comparable to the high-T$_{c}$ cuprates, were obtained. The
$H_{c1}(T)$ and $J_{c}(T)$ dependencies are explained in the context of a
magnetic phase separation scenario.

###Correlation between microstructure and magnetotransport in organic semiconductor spin valve structures|Yaohua Liu,Shannon M. Watson,Taegweon Lee,Justin M. Gorham,Howard E. Katz,Julie A. Borchers,Howard D. Fairbrother,Daniel H. Reich###

Correlation between microstructure and magnetotransport in organic semiconductor spin valve structures. We have studied magnetotransport in organic-inorganic hybrid multilayer
junctions. In these devices, the organic semiconductor (OSC) Alq$_3$
(tris(8-hydroxyquinoline) aluminum) formed a spacer layer between ferromagnetic
(FM) Co and Fe layers. The thickness of the Alq$_3$ layer was in the range of
50-150 nm. Positive magnetoresistance (MR) was observed at 4.2 K in a current
perpendicular to plane geometry, and these effects persisted up to room
temperature. The devices' microstructure was studied by X-ray reflectometry,
Auger electron spectroscopy and polarized neutron reflectometry (PNR). The
films show well-defined layers with modest average chemical roughness (3-5 nm)
at the interface between the Alq$_3$ and the surrounding FM layers.
Reflectometry shows that larger MR effects are associated with smaller
FM/Alq$_3$ interface width (both chemical and magnetic) and a magnetically dead
layer at the Alq$_3$/Fe interface. The PNR data also show that the Co layer,
which was deposited on top of the Alq$_3$, adopts a multi-domain magnetic
structure at low field and a perfect anti-parallel state is not obtained. The
origins of the observed MR are discussed and attributed to spin coherent
transport. A lower bound for the spin diffusion length in Alq$_3$ was estimated
as $43 \pm 5$ nm at 80 K. However, the subtle correlations between
microstructure and magnetotransport indicate the importance of interfacial
effects in these systems.

###Giant anisotropic magnetoresistance through a tilted molecular $π$-orbital|Dongzhe Li,Fabian Pauly,Alexander Smogunov###

Giant anisotropic magnetoresistance through a tilted molecular $π$-orbital. Anisotropic magnetoresistance (AMR), originating from spin-orbit coupling
(SOC), is the sensitivity of the electrical resistance in magnetic systems to
the direction of spin magnetization. Although this phenomenon has been
experimentally reported for several nanoscale junctions, a clear understanding
of the physical mechanism behind it is still elusive. Here we discuss a novel
concept based on orbital symmetry considerations to attain a significant AMR of
up to 95\% for a broad class of $\pi$-type molecular spin-valves. It is
illustrated at the benzene-dithiolate molecule connected between two monoatomic
nickel electrodes. We find that SOC opens, via spin-flip events at the
ferromagnet-molecule interface, a new conduction channel, which is fully
blocked by symmetry without SOC. Importantly, the interplay between main and
new transport channels turns out to depend strongly on the magnetization
direction in the nickel electrodes due to the tilting of molecular orbital.
Moreover, due to multi-band quantum interference, appearing at the band edge of
nickel electrodes, a transmission drop is observed just above the Fermi energy.
Altogether, these effects lead to a significant AMR around the Fermi level,
which even changes a sign. Our theoretical understanding, corroborated in terms
of \textit{ab initio} calculations and simplified analytical models, reveals
the general principles for an efficient realization of AMR in molecule-based
spintronic devices.

###Electrical and Thermal Transport in Antiferromagnet-Superconductor Junctions|Martin F. Jakobsen,Kristian B. Naess,Paramita Dutta,Arne Brataas,Alireza Qaiumzadeh###

Electrical and Thermal Transport in Antiferromagnet-Superconductor Junctions. We demonstrate that antiferromagnet-superconductor (AF-S) junctions show
qualitatively different transport properties than normal metal-superconductor
(N--S) and ferromagnet-superconductor (F-S) junctions. We attribute these
transport features to presence of two new scattering processes in AF--S
junctions, i.e., specular reflection of holes and retroreflection of electrons.
Using the Blonder-Tinkham-Klapwijk formalism, we find that the electrical and
thermal conductance depend nontrivially on antiferromagnetic exchange strength.
Furthermore, we show that the interplay between the N\'eel vector direction and
the interfacial Rashba spin-orbit coupling leads to a large anisotropic
magnetoresistance. The unusual transport properties make AF--S interfaces
unique among the traditional condensed-matter-system-based superconducting
junctions.

###Spin-accumulation in small ferromagnetic double barrier junctions|Arne Brataas,Yu. V. Nazarov,J. Inoue,Gerrit E. W. Bauer###

Spin-accumulation in small ferromagnetic double barrier junctions. The non-equilibrium spin accumulation in ferromagnetic double barrier
junctions is shown to govern the transport in small structures. Transport
properties of such systems are described by a generalization of the theory of
the Coulomb blockade. The spin accumulation enhances the magnetoresistance. The
transient non-linear transport properties are predicted to provide a unique
experimental evidence of the spin-accumulation in the form of a reversed
current on time scales of the order of the spin-flip relaxation time.

###Carbon nanoelectronics: unzipping tubes into graphene ribbons|H. Santos,L. Chico,L. Brey###

Carbon nanoelectronics: unzipping tubes into graphene ribbons. We report on the transport properties of novel carbon nanostructures made of
partially unzipped carbon nanotubes, which can be regarded as a seamless
junction of a tube and a nanoribbon. We find that graphene nanoribbons act at
certain energy ranges as a perfect valley filters for carbon nanotubes, with
the maximum possible conductance. Our results show that a partially unzipped
carbon nanotube is a magnetoresistive device, with a very large value of the
magnetoresistance. We explore the properties of several structures combining
nanotubes and graphene nanoribbons, demonstrating that they behave as optimal
contacts for each other, and opening a new route for the design of mixed
graphene/nanotube devices.

###Molecular Anisotropic Magnetoresistance|Fabian Otte,Stefan Heinze,Yuriy Mokrousov###

Molecular Anisotropic Magnetoresistance. Using density functional theory calculations, we demonstrate that the effect
of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude
with respect to conventional bulk ferromagnets in junctions containing
molecules sandwiched between ferromagnetic leads. We study ballistic transport
in metal-benzene complexes contacted by $3d$ transition-metal wires. We show
that the gigantic AMR can arise from spin-orbit coupling effects in the leads,
drastically enhanced by orbital-symmetry filtering properties of the molecules.
We further discuss how this molecular anisotropic magnetoresistance (MAMR) can
be tuned by proper choice of materials and their electronic properties.

###Cr$_3$X$_4$ (X=Se, Te) monolayers as new platform to realize robust spin filter, spin diode and spin valve|Qihong Wu,Rongkun Liu,Zhanjun Qiu,Dengfeng Li,Jie Li,Xiaotian Wang,Guangqian Ding###

Cr$_3$X$_4$ (X=Se, Te) monolayers as new platform to realize robust spin filter, spin diode and spin valve. Two-dimensional ferromagnetic (FM) half-metals are promising candidates for
advanced spintronic devices with small-size and high-capacity. Motivated by
recent report on controlling synthesis of FM Cr$_3$Te$_4$ nanosheet, herein, to
explore the potential application in spintronics, we designed spintronic
devices based on Cr$_3$X$_4$ (X=Se, Te) monolayers and investigated their spin
transport properties. We found that Cr$_3$Te$_4$ monolayer based device shows
spin filtering and dual spin diode effect when applying bias voltage, while
Cr$_3$S$_4$ monolayer is an excellent platform to realize a spin valve. The
different transport properties are primarily ascribed to the semiconducting
spin channel, which is close to and away from the Fermi level in Cr$_3$Te$_4$
and Cr$_3$Se$_4$ monolayers, respectively. Interestingly, the current in
monolayer Cr$_3$Se$_4$ based device also displays a negative differential
resistance effect (NDRE) and a high magnetoresistance ratio (up to 2*10$^3$).
Moreover, we found thermally induced spin filtering effect and NDRE in
Cr$_3$Se$_4$ junction when applying temperature gradient instead of bias
voltage. These theoretical findings highlight the potential of Cr$_3$X$_4$
(X=Se, Te) monolayers in spintronic applications and put forward realistic
materials to realize nanosale spintronic device.

###Anisotropic Magneto-Thermopower: the Contribution of Interband Relaxation|J. -E. Wegrowe,Q. Anh Nguyen,M. Al-Barki,J. -F. Dayen,T. L. Wade,H. -J. Drouhin###

Anisotropic Magneto-Thermopower: the Contribution of Interband Relaxation. Spin injection in metallic normal/ferromagnetic junctions is investigated
taking into account the anisotropic magnetoresistance (AMR) occurring in the
ferromagnetic layer. It is shown, on the basis of a generalized two channel
model, that there is an interface resistance contribution due to anisotropic
scattering, beyond spin accumulation and giant magnetoresistance (GMR). The
corresponding expression of the thermopower is derived and compared with the
expression for the thermopower produced by the GMR. First measurements of
anisotropic magnetothermopower are presented in electrodeposited Ni nanowires
contacted with Ni, Au and Cu. The results of this study show that while the
giant magnetoresistance and corresponding thermopower demonstrates the role of
spin-flip scattering, the observed anisotropic magnetothermopower indicates
interband s-d relaxation mechanisms.

###Temperature- dependence of anomalous Hall conductivity in Rashba-type ferromagnets|Akimasa Sakuma###

Temperature- dependence of anomalous Hall conductivity in Rashba-type ferromagnets. The applicability and usefulness of Rashba model have been extended by recent
observations in the field of spintronics, such as the spin-orbit torque at the
junction interfaces between ferromagnetic (FM) metals and non-magnetic (NM)
metals and the perpendicular anomalous magnetoresistance (AMR) in
heterostructures such as FI/NM or FM/NI (I denotes an insulator). In
particular, the observations of the perpendicular AMR effect stimulate further
interest in the Rashba-type spin-orbit interaction (SOI) at interfaces. Thus,
the Rashba model with exchange splitting (EXS) is considered not only to play
as an effective model for the physical understanding but also to reflect actual
bi-layer systems in current spintronics devices. In the present work, we have
first investigated the temperature dependence of anomalous Hall conductivity
(AHC) of Rashba-type ferromagnets considered effects of spin fluctuations
within the disordered local moment (DLM) scheme. The most distinctive feature
that we observed is that intrinsic AHC increases with increasing temperature.
This can be understood from the aspect of spin chirality, which indicates that
the AHC increases with decreasing EXS when the SOI is much smaller than the
EXS. The extrinsic part of the Fermi surface term also increases with
increasing temperature and has a large contribution, comparable to that of the
intrinsic part. Although, such a behaviour has not yet been observed
experimentally, we suggest that the physical picture found in this work might
lurk in an anomalous Hall effects in Rashbe-type ferromagnets.

###Unexpected two-fold symmetric superconductivity in few-layer NbSe$_2$|Alex Hamill,Brett Heischmidt,Egon Sohn,Daniel Shaffer,Kan-Ting Tsai,Xi Zhang,Xiaoxiang Xi,Alexey Suslov,Helmuth Berger,László Forró,Fiona J. Burnell,Jie Shan,Kin Fai Mak,Rafael M. Fernandes,Ke Wang,Vlad S. Pribiag###

Unexpected two-fold symmetric superconductivity in few-layer NbSe$_2$. Two-dimensional transition metal dichalcogenides (TMDs) have been attracting
significant interest due to a range of properties, such as layer-dependent
inversion symmetry, valley-contrasted Berry curvatures, and strong spin-orbit
coupling (SOC). Of particular interest is niobium diselenide (NbSe2), whose
superconducting state in few-layer samples is profoundly affected by an unusual
type of SOC called Ising SOC. Combined with the reduced dimensionality, the
latter stabilizes the superconducting state against magnetic fields up to ~35 T
and could lead to other exotic properties such as nodal and crystalline
topological superconductivity. Here, we report transport measurements of
few-layer NbSe$_2$ under in-plane external magnetic fields, revealing an
unexpected two-fold rotational symmetry of the superconducting state. In
contrast to the three-fold symmetry of the lattice, we observe that the
magnetoresistance and critical field exhibit a two-fold oscillation with
respect to an applied in-plane magnetic field. We find similar two-fold
oscillations deep inside the superconducting state in differential conductance
measurements on NbSe$_2$/CrBr$_3$ superconductor-magnet junctions. In both
cases, the anisotropy vanishes in the normal state, demonstrating that it is an
intrinsic property of the superconducting phase. We attribute the behavior to
the mixing between two closely competing pairing instabilities, namely, the
conventional s-wave instability typical of bulk NbSe$_2$ and an unconventional
d- or p-wave channel that emerges in few-layer NbSe2. Our results thus
demonstrate the unconventional character of the pairing interaction in a
few-layer TMD, opening a new avenue to search for exotic superconductivity in
this family of 2D materials.

###Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks|T. Devolder###

Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks. We study how the shape of the spinwave resonance lines in rf-voltage induced
FMR can be used to extract the spinwave density of states and the damping
within the precessing layer in nanoscale tunnel junctions that possess
perpendicular anisotropy. We work with a field applied along the easy axis to
preserve the uniaxial symmetry of the system. We describe the set-up to study
the susceptibility contributions of the spin waves in the field-frequency
space. We then identify the maximum device size above which the spinwaves can
no longer be studied in isolation as the linewidths of their responses make
them overlap. The rf-voltage induced signal is the sum of two voltages that
have comparable magnitudes: a first voltage that originates from the transverse
susceptibility and rectification by magnetoresistance and a second voltage that
arises from the non-linear longitudinal susceptibility and the resultant
time-averaged change of the micromagnetic configuration. The transverse and
longitudinal susceptibility signals have different dc bias dependences such
that they can be separated by measuring how the device rectifies the rf voltage
at different dc bias voltages. The transverse and longitudinal susceptibility
signals have different lineshapes; their joint studies can yield the Gilbert
damping of the free layer of the device with a degree of confidence that
compares well with standard FMR. Our method is illustrated on FeCoB-based free
layers in which the individual spin-waves can be sufficiently resolved only for
disk diameters below 200 nm. The resonance line shapes on devices with 90 nm
diameters are consistent with a Gilbert damping of 0.011. This damping of 0.011
exceeds the value of 0.008 measured on the unpatterned films, which indicates
that device-level measurements are needed for a correct evaluation of
dissipation.

###Ballistic Composite Fermions in Semiconductor Nanostructures|J. E. F. Frost,C. -T. Liang,D. R. Mace,M. Y. Simmons,D. A. Ritchie,M. Pepper###

Ballistic Composite Fermions in Semiconductor Nanostructures. We report the results of two fundamental transport measurements at a Landau
level filling factor $\nu$ of 1/2. The well known ballistic electron transport
phenomena of quenching of the Hall effect in a mesoscopic cross-junction and
negative magnetoresistance of a constriction are observed close to B~=~0 and
$\nu~=~ 1/2$. The experimental results demonstrate semi-classical charge
transport by composite fermions, which consist of electrons bound to an even
number of flux quanta.

###Random resistor network model of minimal conductivity in graphene|V. V. Cheianov,V. I. Falko,B. L. Altshuler,I. L. Aleiner###

Random resistor network model of minimal conductivity in graphene. Transport in undoped graphene is related to percolating current patterns in
the networks of {\em N-} and {\em P}-type regions reflecting the strong bipolar
charge density fluctuations. Transmissions of the {\em P-N} junctions, though
small, are vital in establishing the macroscopic conductivity. We propose a
random resistor network model to analyze scaling dependencies of the
conductance on the doping and disorder, the quantum magnetoresistance and the
corresponding dephasing rate.

###Magnetoresistance through a single molecule|Stefan Schmaus,Alexei Bagrets,Yasmine Nahas,Toyo K. Yamada,Annika Bork,Martin Bowen,Eric Beaurepaire,Ferdinand Evers,Wulf Wulfhekel###

Magnetoresistance through a single molecule. The use of single molecules to design electronic devices is an extremely
challenging and fundamentally different approach to further downsizing
electronic circuits. Two-terminal molecular devices such as diodes were first
predicted [1] and, more recently, measured experimentally [2]. The addition of
a gate then enabled the study of molecular transistors [3-5]. In general terms,
in order to increase data processing capabilities, one may not only consider
the electron's charge but also its spin [6,7]. This concept has been pioneered
in giant magnetoresistance (GMR) junctions that consist of thin metallic films
[8,9]. Spin transport across molecules, i.e. Molecular Spintronics remains,
however, a challenging endeavor. As an important first step in this field, we
have performed an experimental and theoretical study on spin transport across a
molecular GMR junction consisting of two ferromagnetic electrodes bridged by a
single hydrogen phthalocyanine (H2Pc) molecule. We observe that even though
H2Pc in itself is nonmagnetic, incorporating it into a molecular junction can
enhance the magnetoresistance by one order of magnitude to 52%.

###Spin-dependent transport through magnetic nanojunctions|Kamil Walczak,Gloria Platero###

Spin-dependent transport through magnetic nanojunctions. Coherent electronic transport through a molecular device is studied using
non-equilibrium Green's function (NEGF) formalism. Such device is made of a
carbon nanowire which is connected to ferromagnetic electrodes. The molecule
itself is described with the help of Hubbard model (Coulomb interactions are
treated by means of the Hartree-Fock approximation), while the coupling to the
electrodes is modeled through the use of a broad-band theory. It was shown that
magnetoresistance varies periodically with increasing the length of atomic wire
(in the linear response regime) and oscillates with increasing of bias voltage
(in the nonlinear response regime). Since the TMR effect for analyzed
structures is predicted to be large (tens of percentage), considered junctions
seem to be suitable for application as a magnetoresistive elements in the
future electronic circuits.

###Enhancement of Spin Injection into Graphene by Water Dipping|K. M. McCreary,Hua Wen,H. Yu,Wei Han,E. Johnston-Halperin,R. K. Kawakami###

Enhancement of Spin Injection into Graphene by Water Dipping. We immerse single layer graphene spin valves into purified water for a short
duration (<1 min) and investigate the effect on spin transport. Following water
immersion, we observe an enhancement in nonlocal magnetoresistance.
Additionally, the enhancement of spin signal is correlated with an increase in
junction resistance, which produces an increase in spin injection efficiency.
This study provides a simple way to improve the signal magnitude and
establishes the robustness of graphene spin valves to water exposure, which
enables future studies involving chemical functionalization in aqueous
solution.

###Large magnetoresistance dips and perfect spin-valley filter induced by topological phase transitions in silicene|Worasak Prarokijjak,Bumned Soodchomshom###

Large magnetoresistance dips and perfect spin-valley filter induced by topological phase transitions in silicene. Spin-valley transport and magnetoresistance are investigated in
silicene-based N/TB/N/TB/N junction where N and TB are normal silicene and
topological barriers. The topological phase transitions in TB's are controlled
by electric, exchange fields and circularly polarized light. As a result, we
find that by applying electric and exchange fields, four groups of spin-valley
currents are perfectly filtered, directly induced by topological phase
transitions. Control of currents, carried by single, double and triple channels
of spin-valley electrons in silicene junction, may be achievable by adjusting
magnitudes of electric, exchange fields and circularly polarized light. We may
identify that the key factor behind the spin-valley current filtered at the
transition points may be due to zero and non-zero Chern numbers. Electrons that
are allowed to transport at the transition points must obey zero-Chern number
which is equivalent to zero mass and zero-Berry's curvature, while electrons
with non-zero Chern number are perfectly suppressed. Very large
magnetoresistance dips are found directly induced by topological phase
transition points. Our study also discusses the effect of spin-valley dependent
Hall conductivity at the transition points on ballistic transport and reveals
the potential of silicene as a topological material for spin-valleytronics.

###Magnetic domain and magnetic resistance phase transition in strongly correlated electronic material of perovskites junction|Ren R,Weiren Wang,Xuan Li,Zhongxia Zhao###

Magnetic domain and magnetic resistance phase transition in strongly correlated electronic material of perovskites junction. The junction magnetoresistivity and domain phase transition were studied
between ZnO and La0.4Gd0.1Sr0.5CoO3 thin films grown on LaAlO3 (100) substrates
epitaxially by pulse laser deposit. The ferromagnetic transformation into
phase-separated (two phase) state was displayed below Tc~127 and has observed
that the lattice change discontinuously in the doped cobalt perovskites
La0.4Gd0.1Sr0.5CoO3. The Ginzburg-Landau phase field is introduced to deduce
antiferroelectric domain structure in LGSCO thin film. On the basis of the
domain structures, the phase boundary of thin film is strongly dependent on the
combination of electric-mechanical coupling. The phase transformation into
phase separated state occurs below Tc~127-128K, and have displayed that the
lattice constants change discontinuously at the transformation. The positive MR
of ZnO/LGSCO heterojunction exhibited the MIT behavior at 0.2 T is 4.86%, at
0.5 T is 6.05% for approximately 140K.

###High density carriers at a strongly coupled graphene-topological insulator interface|Ayelet Zalic,Tom Dvir,Hadar Steinberg###

High density carriers at a strongly coupled graphene-topological insulator interface. We report on a strongly coupled bilayer graphene (BLG) - \bise\ device with a
junction resistance of less than 1.5 k$\Omega\mu$m$^2$. This device exhibits
unique behavior at the interface, which cannot be attributed to either material
in absence of the other. We observe quantum oscillations in the
magnetoresistance of the junction, indicating the presence of well-resolved
Landau levels due to hole carriers of unknown origin with a very large Fermi
surface. These carriers, found only at the interface, could conceivably arise
due to significant hole doping of the bilayer graphene with charge transfer on
the order of 2$\times$10$^{13}$ cm$^{-2}$, or due to twist angle dependent
mini-band transport.

###Spin-memory loss at Co/Ru interfaces|Mazin A. Khasawneh,Carolin Klose,W. P. Pratt, Jr.,Norman O. Birge###

Spin-memory loss at Co/Ru interfaces. We have determined the spin-memory-loss parameter, $\delta_{Co/Ru}$, by
measuring the transmission of spin-triplet and spin-singlet Cooper pairs across
Co/Ru interfaces in Josephson junctions and by Current-Perpendicular-to-Plane
Giant Magnetoresistance (CPP-GMR) techniques. The probability of spin-memory
loss at the Co/Ru interface is $(1-exp(-\delta_{Co/Ru}))$. From the CPP-MR, we
obtain $\delta_{Co/Ru} = 0.34^{+0.04}_{-0.02}$ that is in good agreement with
$\delta_{Co/Ru} = 0.35 \pm 0.08$ obtained from spin-triplet transmission. For
spin-singlet transmission, we have $\delta_{Co/Ru} = 0.64 \pm 0.05$ that is
different from that obtained from CPP-GMR and spin-triplet transmission. The
source of this difference is not understood.

###Molecular Beam Epitaxial Growth of Bi2Te3 and Sb2Te3 Topological Insulators on GaAs (111) Substrates: A Potential Route to Fabricate Topological Insulator p-n Junction|Zhaoquan Zeng,Timothy A. Morgan,Dongsheng Fan,Chen Li,Yusuke Hirono,Xian Hu,Yanfei Zhao,Joon Sue Lee,Zhiming M. Wang,Jian Wang,Shuiqing Yu,Michael E. Hawkridge,Mourad Benamara,Gregory J. Salamo###

Molecular Beam Epitaxial Growth of Bi2Te3 and Sb2Te3 Topological Insulators on GaAs (111) Substrates: A Potential Route to Fabricate Topological Insulator p-n Junction. High quality Bi2Te3 and Sb2Te3 topological insulators films were epitaxially
grown on GaAs (111) substrate using solid source molecular beam epitaxy. Their
growth and behavior on both vicinal and non-vicinal GaAs (111) substrates were
investigated by reflection high-energy electron diffraction, atomic force
microscopy, x-ray diffraction, and high resolution transmission electron
microscopy. It is found that non-vicinal GaAs (111) substrate is better than a
vicinal substrate to provide high quality Bi2Te3 and Sb2Te3 films. Hall and
magnetoresistance measurements indicate that p type Sb2Te3 and n type Bi2Te3
topological insulator films can be directly grown on a GaAs (111) substrate,
which may pave a way to fabricate topological insulator p-n junction on the
same substrate, compatible with the fabrication process of present
semiconductor optoelectronic devices.

###Effects of carrier mobility and morphology in organic semiconductor spin valves|Yaohua Liu,Taegweon Lee,Howard E. Katz,Daniel H. Reich###

Effects of carrier mobility and morphology in organic semiconductor spin valves. We studied spin transport in four organic semiconductors (OSCs) with
different electronic properties, with Fe and Co as the top and bottom
ferromagnetic (FM) contacts, respectively. Magnetoresistance (MR) effects were
observed up to room temperature in junctions based on an electron-carrying OSC,
tris(8-hyroxyquinoline) aluminum (Alq$_3$) and a hole-carrying OSC, copper
phthalocyanine (CuPc). The MR shows similar temperature dependence for these
two OSCs, which suggests that the FM leads rather than the OSCs play a dominant
role on the spin-transport degradation with increasing temperature. We also
investigated junctions based on two high lateral mobility electron-carrying
OSCs, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and N,
N'-bis(4-trifluoromethylbenzyl)-1,4,5,8-naphthalenetetracarboxylic diimide
(CF$_3$-NTCDI). However, these junctions showed much weaker spin transport
effects. Morphological studies suggest that these high mobility OSC films have
much rougher surfaces than either Alq$_3$ or CuPc, therefore the degradation of
spin transport may originate from enhanced scattering due to the rougher FM/OSC
interfaces. Our study shows that FM/OSC interfaces play an important role for
spin transport in organic devices and need further exploration.

###Characterization of one-dimensional quantum channels in InAs/AlSb|C. H. Yang,M. J. Yang,K. A. Cheng,J. C. Culbertson###

Characterization of one-dimensional quantum channels in InAs/AlSb. We report the magnetoresistance characteristics of one-dimensional electrons
confined in a single InAs quantum well sandwiched between AlSb barriers. As a
result of a novel nanofabrication scheme that utilizes a 3nm-shallow wet
chemical etching to define the electrostatic lateral confinement, the system is
found to possess three important properties: specular boundary scattering, a
strong lateral confinement potential, and a conducting channel width that is
approximately the lithography width. Ballistic transport phenomena, including
the quenching of the Hall resistance, the last Hall plateau, and a strong
negative bend resistance, are observed at 4K in cross junctions with sharp
corners. In a ring geometry, we have observed Aharonov-Bohm interference that
exhibits characteristics different from those of the GaAs counterpart due to
the ballistic nature of electron transport and the narrowness of the conducting
channel width.

###Controllable Josephson current through a pseudo-spin-valve structure|C. Bell,G. Burnell,C. W. Leung,E. J. Tarte,D. -J. Kang,M. G. Blamire###

Controllable Josephson current through a pseudo-spin-valve structure. A thin Co/Cu/Permalloy (Ni$_{80}$Fe$_{20}$) pseudo-spin-valve structure is
sandwiched between superconducting Nb contacts. When the current is passed
perpendicular to the plane of the film a Josephson critical current ($I_C$) is
observed at 4.2 K, in addition to a magnetoresistance (MR) of $\sim$ 0.5 % at
high bias. The hysteresis loop of the spin-valve structure can be cycled to
modulate the zero field $I_C$ of the junction in line with the MR measurements.
These modulations of resistance and $I_C$ occur both smoothly and sharply with
the applied field. For each type of behaviour there is a strong correlation
between shape of the MR loops and the $I_C$ modulation.

###Giant resistance change across the phase transition in spin crossover molecules|N. Baadji,S. Sanvito###

Giant resistance change across the phase transition in spin crossover molecules. The electronic origin of a large resistance change in nanoscale junctions
incorporating spin crossover molecules is demonstrated theoretically by using a
combination of density functional theory and the non-equilibrium Green's
functions method for quantum transport. At the spin crossover phase transition
there is a drastic change in the electronic gap between the frontier molecular
orbitals. As a consequence, when the molecule is incorporated in a two terminal
device, the current increases by up to four orders of magnitude in response to
the spin change. This is equivalent to a magnetoresistance effect in excess of
3,000 %. Since the typical phase transition critical temperature for spin
crossover compounds can be extended to well above room temperature, spin
crossover molecules appear as the ideal candidate for implementing spin devices
at the molecular level.

###Probe of Spin Dynamics in Superconducting NbN Thin Films via Spin Pumping|Yunyan Yao,Qi Song,Yota Takamura,Juan Pedro Cascales,Wei Yuan,Yang Ma,Yu Yun,X. C. Xie,Jagadeesh S. Moodera,Wei Han###

Probe of Spin Dynamics in Superconducting NbN Thin Films via Spin Pumping. The emerging field of superconductor (SC) spintronics has attracted intensive
attentions recently. Many fantastic spin dependent properties in SC have been
discovered, including the observation of large magnetoresistance, long spin
lifetimes and the giant spin Hall effect in SC, as well as spin supercurrent in
Josephson junctions, etc. Regarding the spin dynamic in SC films, few studies
has been reported yet. Here, we report the investigation of the spin dynamics
in an s-wave superconducting NbN film via spin pumping from an adjacent
insulating ferromagnet GdN layer. A profound coherence peak of the Gilbert
damping is observed slightly below the superconducting critical temperature of
the NbN layer, which is consistent with recent theoretical studies. Our results
further indicate that spin pumping could be a powerful tool for investigating
the spin dynamics in 2D crystalline superconductors.

###Charging effects and anomalous resistive features of superconducting boron doped diamond films|Christopher Coleman,Somnath Bhattacharyya###

Charging effects and anomalous resistive features of superconducting boron doped diamond films. Anomalous resistive peaks below the superconducting transition temperature in
heavily boron doped nanocrystalline diamond films could have potential
application in switching devices, however the exact origin is still under
study. We establish a temperature dependence of this resistive phase similar to
what has been reported for in Josephson junction arrays and other granular
superconductors where the charge duel of the Berezinskii-Kosterlitz-Thouless
(BKT) transition has been observed. Non-linear magnetoresistance with a
temperature dependent peak feature below the critical field are also presented.
Pronounced temperature dependent hysteresis in the current voltage sweeps at
temperatures below the determined BKT critical point are related to pinning of
charge defects. It is shown that these collective features allude to a
Charge-BKT transition between charge and anti-charge analogues.

###Tuning spin filtering by anchoring groups in benzene derivative molecular junctions|Dongzhe Li,Yannick J. Dappe,Alexander Smogunov###

Tuning spin filtering by anchoring groups in benzene derivative molecular junctions. One of the important issues of molecular spintronics is the control and
manipulation of charge transport and, in particular, its spin polarization
through single-molecule junctions. Using $ab$ $initio$ calculations, we explore
spin-polarized electron transport across single benzene derivatives attached
with six different anchoring groups (S, CH$_3$S, COOH, CNH$_2$NH, NC and
NO$_2$) to Ni(111) electrodes. We find that molecule-electrode coupling,
conductance and spin polarization (SP) of electric current can be modified
significantly by anchoring groups. In particular, a high spin polarization (SP
$>$ 80%) and a giant magnetoresistance (MR $>$ 140%) can be achieved for NO$_2$
terminations and, more interestingly, SP can be further enhanced (up to 90%) by
a small voltage. The S and CH$_3$S systems, on the contrary, exhibit rather low
SP while intermediate values are found for COOH and CNH$_2$NH groups. The
results are analyzed in detail and explained by orbital symmetry arguments,
hybridization and spatial localization of frontier molecular orbitals. We hope
that our comparative and systematic studies will provide valuable quantitative
information for future experimental measurements on that kind of systems and
will be useful for designing high-performance spintronics devices.

###Electrical spin injection and detection in a semiconductor. Is it feasible?|A. T. Filip,B. H. Hoving,F. J. Jedema,B. J. van Wees###

Electrical spin injection and detection in a semiconductor. Is it feasible?. The electrical injection of spin polarized electrons in a semiconductor can
be achieved in principle by driving a current from a ferromagnetic metal, where
current is known to be significantly spin polarized, into the semiconductor via
ohmic conduction. For detection a second ferromagnet can be used as drain. We
studied submicron lateral spin valve junctions, based on high mobility
InAs/AlSb two-dimensional electron gas (2DEG), with Ni, Co and Permalloy as
ferromagnetic electrodes. In the standard geometry it is very difficult to
separate true spin injection from other effects, including local Hall effect,
anomalous magnetoresistance (AMR) contribution from the ferromagnetic
electrodes and weak localization/anti-localization corrections, which can
closely mimic the signal expected from spin valve effect. The reduction in
size, and the use of a multiterminal non-local geometry allowed us to reduce
the unwanted effects to a minimum. Despite all our efforts, we have not been
able to observe spin injection. However, we find that this 'negative' result in
these systems is actually consistent with theoretical predictions for spin
transport in diffusive systems.

###Point contact investigations of film and interface magnetoresistance of La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructures on Nb:SrTiO$_{3}$|Asmund Monsen,Jos E. Boschker,Per Nordblad,Roland Mathieu,Thomas Tybell,Erik Wahlström###

Point contact investigations of film and interface magnetoresistance of La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructures on Nb:SrTiO$_{3}$. STM based magnetotransport measurements of epitaxial
La$_{0.7}$Sr$_{0.3}$MnO$_3$ 32 nm thick films with and without an internal
LaMnO$_3$ layer (0-8 nm thick) grown on Nb doped SrTiO$_3$ are presented. The
measurements reveal two types of low field magnetoresistance (LFMR) with a
magnitude of $\sim 0.1-1.5\%$. One LFMR contribution is identified as a
conventional grain boundary/domain wall scattering through the symmetric I-V
characteristics, high dependence on tip placements and insensitivity to
introduction of LaMnO$_3$ layers. The other contribution originates from the
reverse biased Nb doped SrTiO$_3$ interface and the interface layer of
La$_{0.7}$Sr$_{0.3}$MnO$_3$. Both LFMR contributions display a field dependence
indicative of a higher coercivity ($\sim$200 Oe) than the bulk film. LaMnO$_3$
layers are found to reduce the rectifying properties of the junctions, and sub
micron lateral patterning by electron beam lithography enhances the diodic
properties, in accordance with a proposed transport model based on the locality
of the injected current.

###Dynamical Mean-Field Theory for spin-dependent electron transport in spin-valve devices|Andrea Droghetti,Milos M. Radonjić,Liviu Chioncel,Ivan Rungger###

Dynamical Mean-Field Theory for spin-dependent electron transport in spin-valve devices. We present the combination of Density Functional Theory (DFT) and Dynamical
Mean Field Theory (DMFT) for computing the electron transmission through
two-terminals nanoscale devices. The method is then applied to metallic
junctions presenting alternating Cu and Co layers, which exhibit spin-dependent
charge transport and giant magnetoresistance (GMR) effect. The calculations
show that the coherent transmission through the $3d$ states is greatly
suppressed by electron correlations. This is mainly due to the finite lifetime
induced by the electron-electron interaction and is directly related to the
imaginary part of the computed many-body DMFT self-energy. At the Fermi energy,
where in accordance with the Fermi-liquid behavior the imaginary part of the
self-energy vanishes, the suppression of the transmission is entirely due to
the shifts of the energy spectrum induced by electron correlations. Based our
results, we finally suggest that the GMR measured in Cu/Co heterostructures for
electrons with energies about 1 eV above the Fermi energy is a clear
manifestation of dynamical correlation effects.

###Observation of Quantum Interference in Molecular Charge Transport|Constant M. Guedon,Hennie Valkenier,Troels Markussen,Kristian S. Thygesen,Jan C. Hummelen,Sense Jan van der Molen###

Observation of Quantum Interference in Molecular Charge Transport. As the dimensions of a conductor approach the nano-scale, quantum effects
will begin to dominate its behavior. This entails the exciting possibility of
controlling the conductance of a device by direct manipulation of the electron
wave function. Such control has been most clearly demonstrated in mesoscopic
semiconductor structures at low temperatures. Indeed, the Aharanov-Bohm effect,
conductance quantization and universal conductance fluctuations are direct
manifestations of the electron wave nature. However, an extension of this
concept to more practical emperatures has not been achieved so far. As
molecules are nano-scale objects with typical energy level spacings (~eV) much
larger than the thermal energy at 300 K (~25 meV), they are natural candidates
to enable such a break-through. Fascinating phenomena including giant
magnetoresistance, Kondo effects and conductance switching, have previously
been demonstrated at the molecular level. Here, we report direct evidence for
destructive quantum interference in charge transport through two-terminal
molecular junctions at room temperature. Furthermore, we show that the degree
of interference can be controlled by simple chemical modifications of the
molecule. Not only does this provide the experimental demonstration of a new
phenomenon in quantum charge transport, it also opens the road for a new type
of molecular devices based on chemical or electrostatic control of quantum
interference.