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Here we show that ordinary band-structure codes can be used to understand the mechanisms of coherent spin-injection at interfaces between ferromagnets and semiconductors. This approach allows the screening of different material combinations for properties useful for obtaining high tunneling magnetoresistance (TMR). We used the Vienna Ab-initio Simulation Code (VASP) to calculate the wave-function character of each band in periodic epitaxial Fe(100)|GaAs(100) and Fe(100)|ZnSe(100) structures. It is shown that Fe wave functions of different symmetry near Fermi energy decay differently in the GaAs and ZnSe. [ABSTRACT FROM AUTHOR]

In this work we demonstrate explicit analytical expressions for both charge and spin currents which constitute the 2 × 2 spinor in magnetic tunnel junctions with noncollinear magnetizations under applied voltage. The calculations have been performed within the free electron model in the framework of the Keldysh formalism and WKB approximation. We demonstrate that spin/charge currents and spin transfer torques are all explicitly expressed through only three irreducible quantities, without further approximations. The conditions and mechanisms of deviation from the conventional sine angular dependence of both spin currents and torques are shown and discussed. It is shown in the thick barrier approximation that all tunneling transport quantities can be expressed in an extremely simplified form via Slonczewski spin polarizations and our effective spin averaged interfacial transmission probabilities and effective out-of-plane polarizations at both interfaces. It is proven that the latter plays a key role in the emergence of perpendicular spin torque as well as in the angular dependence character of all spin and charge transport considered. It is demonstrated directly also that for any applied voltage, the parallel component of spin current at the FM/I interface is expressed via collinear longitudinal spin current components. Finally, spin transfer torque behavior is analyzed in a view of transverse characteristic length scales for spin transport. [ABSTRACT FROM AUTHOR]

Nonequilibrium spin-dependent transport in magnetic tunnel junctions comprising a ferroelectric barrier is theoretically investigated. The exact solutions of the free electron Schrödinger equation for electron tunneling in the presence of interfacial screening are obtained by combining Bessel and Airy functions. We demonstrate that the spin transfer torque efficiency, and more generally the bias dependence of tunneling magneto- and electroresistance, can be controlled by switching the ferroelectric polarization of the barrier. In particular, the critical voltage at which the in-plane torque changes sign can be strongly enhanced or reduced depending on the direction of the ferroelectric polarization of the barrier. This effect provides a supplementary way to electrically control the current-driven dynamic states of the magnetization and related magnetic noise in spin transfer devices. [ABSTRACT FROM AUTHOR]

The perpendicular magnetic anisotropy (PMA) arising at the interface between ferromagnetic transition metals and metallic oxides was investigated via first-principles calculations. In this work very large values of PMA, up to 3 erg/cm2, at Fe∣MgO interfaces are reported, in agreement with recent experiments. The origin of PMA is attributed to overlap between O-pz and transition metal dz2 orbitals hybridized with dxz(yz) orbitals with stronger spin-orbit coupling-induced splitting around the Fermi level for perpendicular magnetization orientation. Furthermore, it is shown that the PMA value weakens in the case of over- or underoxidation due to the fact that oxygen pz and transition metal dz2 orbital overlap is strongly affected by disorder, in agreement with experimental observations in magnetic tunnel junctions. [ABSTRACT FROM AUTHOR]

Theoretical investigations of spin transfer torque in magnetic tunnel junctions using the tight-binding model in the framework of nonequilibrium Green functions formalism are presented. We show that the behavior of the spin transfer torque as a function of applied voltage can vary over a wide range depending on the band parameters of the ferromagnetic electrodes and the insulator that comprise the magnetic tunnel junction. The behavior of both the parallel and perpendicular components of the spin torque is addressed. This behavior is explained in terms of the spin and charge current dependence and on the interplay between evanescent states in the insulator and the Fermi surfaces of ferromagnetic electrodes comprising the junction. The origin of the perpendicular (field-like) component of spin transfer torque at zero bias, i.e., exchange coupling through the barrier between ferromagnetic electrodes is discussed. [ABSTRACT FROM AUTHOR]

The effect of structural relaxation and interfacial oxidation is demonstrated from first principles to have a crucial impact on interlayer exchange coupling (IEC) in crystalline Fe|MgO|Fe magnetic tunnel junctions (MTJs). It is shown that the IEC becomes antiferromagnetic for the relaxed structure in contrast to ferromagnetic for unrelaxed Fe|MgO|Fe MTJs. Furthermore, the antiferromagnetic IEC is strongly enhanced in the presence of oxygen vacancies while it is decreased by overoxidation and may even become ferromagnetic for sufficiently high oxygen concentration at the Fe|MgO interface. These results were supported using a tight-binding model and provide an explanation for recent experimental studies. [ABSTRACT FROM AUTHOR]

Quantum coherent transport in double barrier tunnel junctions has been exploited for building micrometric-size semiconductor-free diodes. At room temperature, we observe strongly asymmetric current-voltage characteristics with an asymmetry ratio increasing with the bias voltage, reaching a maximum of 20 at 1 V. Our experimental data can be perfectly explained using a theoretical model involving resonance-assisted tunneling. The coherent/resonant tunneling regime is achieved using metallic 3 nm diameter monodisperse Cu clusters, sandwiched between two Al[sub 2]O[sub 3] barriers. © 2001 American Institute of Physics. [DOI: 10.1063/1.1426685]. [ABSTRACT FROM AUTHOR]

A number of L21 phase alloys (composition X2YZ) are half-metallic. Although this structure is typically described in terms of a fcc Bravais lattice with a four atom basis, it can be viewed more simply as a variant of bcc or B2 in which planes of X2 alternate with planes of YZ along the 001 direction. Using ab initio electronic structure calculations, we have investigated planar insertions along 001 into the L21 structure. For most scenarios, insertion of single or double atomic layers of Cr into Co2MnGe or Co2MnSi did not destroy the half-metallic property. One insertion of a Cr layer into Co2MnGe was observed to increase the gap. In fact, we observed that for a large number of insertions using various transition metals or combinations of transition metals and nontransition metals, the band gap in the minority channel at the Fermi energy remains. An ad hoc rule that seems to partially capture the tendency to form half-metals can be formulated as: “001 planar insertions that can plausibly yield eight down spin electrons on the X2 layer and four down spin electrons on the YZ layer yield half-metals.” [ABSTRACT FROM AUTHOR]

The relative contributions of in-plane (damping-like) and out-of-plane (field-like) spin-transfer torques (STT) in the magnetization switching of out-of-plane magnetized magnetic tunnel junctions (pMTJ) has been theoretically analyzed using the transformed Landau-Lifshitz-Gilbert (LLG) equation with the STT terms. It is demonstrated that in a pMTJ structure obeying macrospin dynamics, the out-of-plane torque influences the precession frequency, but it does not contribute significantly to the STT switching process (in particular to the switching time and switching current density), which is mostly determined by the in-plane STT contribution. This conclusion is confirmed by finite temperature and finite writing pulse macrospin simulations of the current field switching diagrams. It contrasts with the case of STT switching in in-plane magnetized magnetic tunnel junction (MTJ) in which the field-like term also influences the switching critical current. This theoretical analysis was successfully applied to the interpretation of voltage field STT switching diagrams experimentally measured on pMTJ pillars 36 nm in diameter, which exhibit macrospin behavior. The physical nonequivalence of Landau and Gilbert dissipation terms in the presence of STT-induced dynamics is also discussed. [ABSTRACT FROM AUTHOR]

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 interfacial PMA while reducing the bulk magnetization and correlatively the easy-plane demagnetizing energy. As a result, the effective magnetic anisotropy tends to increase as a function of the Cr or V concentration resulting in an increase in the critical magnetic thickness at which the crossover from out-of-plane to in-plane anisotropy takes place. At the same time, the interfacial spin polarization is not affected by the magnetic layer bulk doping by Cr or V impurities and even enhanced in most situations thus favoring an increase of tunnel magnetoresistance (TMR) amplitude. [ABSTRACT FROM AUTHOR]

Endurance of MgO-based magnetic tunnel junctions has been studied using a time-dependent dielectric breakdown method. Series of successive electrical pulses were applied until electrical breakdown of the tunnel barrier. We show that two electrical breakdown regimes exist depending on the time interval Δt between pulses compared to a characteristic escape time of trapped electrons τ0 ∼ 100 ns. For Δt < τ0, breakdown is caused by a high average charge trapped in the barrier. For Δt > τ0, breakdown is ascribed to large temporal modulation of trapped charges causing alternating stress in the barrier oxide. Between these two regimes, the tunnel junctions reach a very high endurance. [ABSTRACT FROM AUTHOR]

First-principles calculations of the electronic structures of chalcogenide spinels with anion vacancy and substitutions are presented. Our calculations predict that Cu(Cd)Cr2S(Se)4-x, CuCr2S(Se)4-xEx (E=F, Cl, Br), and CdCr2S(Se)4-xDx (D=N, P, As) can be half-metallic over a range of concentrations. The magnetic moment is found to scale approximately linearly on adding or withdrawing electrons and varies between 5.0 and 6.0 μB/f.u. [ABSTRACT FROM AUTHOR]

First-principles calculations indicate that the chalcogenide spinels CdxCu1-xCr2S4 and CdxCu1-xCr2Se4 can be ferromagnetic metals, half-metals, or semiconductors depending on the Cd concentration x. In particular, CdxCu1-xCr2S4 can be tuned to be effectively half-metallic for x values between 0.25 and 0.875 and CdxCu1-xCr2Se4 can be half-metallic for x between 0.625 and 0.875. For x<0.25 for CdxCu1-xCr2S4 and for x<0.625 for CdxCu1-xCr2Se4, these materials are predicted to be ferromagnetic metals. For x>0.875 both systems are predicted to be ferromagnetic semiconductors. [ABSTRACT FROM AUTHOR]

One of important characteristics of a magnetic tunneling junction (MTJ) nanoheterostructure that is used as magnetic random access memory (MRAM) cell and is switched by the spin transfer torque (STT) effect is its stability diagram, which determines the range of values of the external magnetic field and applied voltage under which a cell is in one of two stable states. To numerically construct such diagrams, one usually uses the solution of the Landau–Lifshitz dynamic equation in the single-domain approximation along with phenomenological constants that determine the values of spin torque in the material. In the present paper, the problem of spin-dependent electron transfer in an MTJ structure is considered, whose solution in the free-electron approximation allows one to calculate the values of spin torque for a given material in any magnetic configuration of the system and apply them to the integration of the Landau–Lifshitz equation. The method used allows one to more precisely reproduce the shape of the stability diagram and predict the critical values of the magnetic field and voltage necessary to switch an MTJ-based MRAM cell. [ABSTRACT FROM AUTHOR]

Theoretical studies of spin dependent transport in Fe/Cr/MgO/Fe tunnel junctions with noncollinear alignment of magnetizations of metallic layers comprising these magnetic tunnel junctions are presented. Calculations are performed with use of nonequilibrium Green function technique in the framework of the Keldysh formalism. Electronic band structure of ferromagnetic electrodes is modeled within a two-band model with majority and minority states being s-like and d-like electrons, respectively. Furthermore, interfacial s-d hybridization is taken into account and calculated using perturbation corrections for the wave and Green functions. It is shown that in the presence of Cr layer at the Fe/MgO interface, the contribution from s-d hybridization to the total current is much stronger in the antiparallel magnetizations configuration compared to the parallel one leading to decrease in tunnel magnetoresistance values in agreement with earlier reports. [ABSTRACT FROM AUTHOR]

Recent experiments indicate that films of V1-xCrxO2 may be obtained which retain the tetragonal rutile phase to low temperature. In order to better understand this system we have calculated its electronic structure using density functional theory in the generalized gradient approximation and density functional theory with empirical on-site Coulomb correlations (LDA+U). Within these approximations we find that the ground state of rutile phase V1-xCrxO2 is quite simple. Both V and Cr are in the +4 state, implying that the V and Cr ions have moments of 1μB and 2μB, respectively. Similar to CrO2, V1-xCrxO2 is predicted to be ferromagnetic and half-metallic. Our results appear to be consistent with the experimental observations that VO2 is paramagnetic and metallic for temperatures above 340 K where it is stable. It is not clear, however, that these results are completely consistent with recent experimental observations of ferromagnetism at low temperature in V1-xCrxO2 for x=0.1 and x=0.2. [ABSTRACT FROM AUTHOR]

We present tight-binding calculations of the spin torque in noncollinear magnetic tunnel junctions based on the nonequilibrium Green functions approach. We have calculated the spin torque via the effective local magnetic moment approach and the divergence of the spin current. We show that both methods are equivalent, i.e., the absorption of the spin current at the interface is equivalent to the exchange interaction between the electron spins and the local magnetization. The transverse components of the spin torque parallel and perpendicular to the interface oscillate with different phase and decay in the ferromagnetic layer (FM) as a function of the distance from the interface. The period of oscillations is inversely proportional to the difference between the Fermi momentum of the majority and minority electrons. The phase difference between the two transverse components of the spin torque is due to the precession of the electron spins around the exchange field in the FM layer. In the absence of applied bias and for a relatively thin barrier, the component of the spin torque perpendicular to the interface is nonzero due to the exchange coupling between the FM layers across the barrier. [ABSTRACT FROM AUTHOR]

The charge-mediated effect of electric field on the perpendicular magnetic anisotropy (PMA) of Fe/MgO interfaces is investigated using first-principles calculations. We present an approach by discussing this effect in relation to the intrinsic dipole field existing at the Fe/MgO interface. A firm correlation between the PMA and the interfacial dipole is established and further verified in the absence of an applied electric field. The on-site projected PMA analysis not only elucidates that the effect of electric field on the PMA extends beyond the interfacial Fe layer, but also shows that the second Fe layer carries the largest contribution to the effect. This observation is interpreted in relation to the orbital hybridization changes induced by applying an electric field. [ABSTRACT FROM AUTHOR]

Double-barrier heterostructures are model systems for the study of electron tunneling and discrete energy levels in a quantum well (QW). Until now resonant tunneling phenomena in metallic QWs have been observed for limited thicknesses (1-2 nm) under which electron phase coherence is conserved. In the present study we show evidence of QW resonance states in Fe QWs up to 12 nm thick and at room temperature in fully epitaxial double MgA10c barrier magnetic tunnel junctions. The electron phase coherence displayed in this QW is of unprecedented quality because of a homogenous interface phase shift due to the small lattice mismatch at the Fe-MgA10v interface. The physical understanding of the critical role of interface strain on QW phase coherence will greatly promote the development of spin-dependent quantum resonant tunneling applications. [ABSTRACT FROM AUTHOR]

Magnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pave the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated. [ABSTRACT FROM AUTHOR]

Spin-transfer torque (STT) in tunnel junctions with ferromagnetic leads is one of the essential underlying phenomena of modem spintronics. Here, we present a theoretical study of STT in ferrimagnet- (FT-) based tunnel junctions where two FI metal electrodes are separated by a thin nonmagnetic insulating barrier. We show that electronic structure parameters, such as bandwidths and exchange splittings of the FI leads strongly influence STT. In particular, the STT spatial distribution within the leads shows a striking spin-modulated wavelike behavior resulting from the interplay between the exchange splittings of the two FI sublattices. Additionally, we identify the fundamental parameter for quantifying STT characteristic lengths in FI metals, which will also be accessible to experiments, for instance, by ferromagnetic resonance and spin pumping measurements. [ABSTRACT FROM AUTHOR]

We investigate the behaviour of spin transfer torque (STT) and tunnelling magnetoresistance (TMR) in epitaxial antiferromagnetic-based tunnel junctions using tight binding calculations in the framework of the Keldysh formalism. We find that the STT out-of-plane component exhibits a staggered spatial distribution similar to its in-plane component. This behaviour is specific to the use of a tunnel barrier and significantly differs from the out-of-plane torques reported in previous works using a metallic spacer. Additionally, we show that unlike conventional ferromagnetic-based tunnel junctions, the TMR can increase with applied bias and reach values comparable to typical magnetoresistances found for usual spin valves. [ABSTRACT FROM AUTHOR]

Binary information encoded within the spin of carriers can be transferred into corresponding right- or left-handed circularly polarized photons emitted from an active semiconductor medium via carrier-photon angular momentum conversion. In order to attain maximized spin injection at out-of-plane magnetic remanence, a number of material systems have been explored as possible solid-state spin injectors. However, the circular polarization (Pc) of emitted light was still limited at 3-4% at remanence. Here, we demonstrate a sizable electroluminescence circular polarization from a III-V-based spin light-emitting diode at zero magnetic field with a perpendicular spin injector consisting of an ultrathin CoFeB ferromagnetic layer (1.2 nm) grown on a MgO tunnel barrier (2.5 nm). The maximum value of Pc measured at zero field is as large as 20% at 25 K and still 8% at 300 K. These types of ultrathin perpendicular spin injectors are of great interest (i) to realize the electrical switching of the magnetization of the injector layer owing to the advanced spin-transfer torque properties of the CoFeB layer and (ii) to be directly embedded in optical cavities for spin lasers due to their very low optical absorption loss. [ABSTRACT FROM AUTHOR]

Spintronics relies on the spin dependent transport properties of ferromagnets (Fs). Although antiferromagnets (AFs) are used for their magnetic properties only, some fundamental F-spintronics phenomena like spin transfer torque, domain wall motion, and tunnel anisotropic magnetoresistance also occur with AFs, thus making AF-spintronics attractive. Here, room temperature critical depths and absorption mechanisms of spin currents in Ir20Mn80 and Fe50Mn50 are determined by F-resonance and spin pumping. In particular, we find room temperature critical depths originating from different absorption mechanisms: dephasing for Ir20Mn80 and spin flipping for Fe50Mn50. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, we elucidate microscopic mechanisms of perpendicular magnetic anisotropy (PMA) in Fe/MgO magnetic tunnel junctions through evaluation of orbital and layer resolved contributions into the total anisotropy value. It is demonstrated that the origin of the large PMA values is far beyond simply considering the hybridization between Fe-3d and O-2p orbitals at the interface between the metal and the insulator. Onsite projected analysis shows that the anisotropy energy is not localized at the interface but it rather propagates into the bulk showing an attenuating oscillatory behavior which depends on orbital character of contributing states and interfacial conditions. Furthermore, it is found in most situations that states with dyz(xz) and dZ2 character tend always to maintain the PMA while those with dxy and dx2-y2 character tend to favor the in-plane anisotropy. It is also found that while MgO thickness has no influence on PMA, the calculated perpendicular magnetic anisotropy oscillates as a function of Fe thickness with a period of 2 ML and reaches a maximum value of 3.6 mJ/m2. [ABSTRACT FROM AUTHOR]

Unique atomic structures at the edges of graphenes yield a variety of interesting phenomena. In spite of carbon-based material with only sp bonds, the zigzag-type atomic structure of graphene edges theoretically produces spontaneous spin polarization of electrons due to mutual Coulomb interaction of extremely high electron density of states localizing at the flat energy band. However, spin-based phenomena have been experimentally observed only in defect-related carbon systems. Here, we fabricate honeycomb-like arrays of low-defect hexagonal nanopores (graphene nanomeshes; GNMs) on graphenes, which produce a large amount of pore edges, by using a nonlithographic method (nanoporous alumina templates). We find large-magnitude ferromagnetism arising from polarized electron spins localizing at the zigzag-nanopore edges of monolayer GNMs. Moreover, spin pumping effect depending on GNM structures is found for magnetic fields applied in parallel with the few-layer GNM planes. These promise to be a realization of rare-element free magnets and also novel all-carbon spintronic devices. [ABSTRACT FROM AUTHOR]

We report on first-principles calculations of spin-dependent properties in graphene induced by its interaction with a nearby magnetic insulator (europium oxide, EuO). The magnetic proximity effect results in spin polarization of graphene π orbitals by up to 24%, together with a large exchange-splitting band gap of about 36 meV. The position of the Dirac cone is further shown to depend strongly on the graphene-EuO interlayer. These findings point toward the possible engineering of spin gating by the proximity effect at a relatively high temperature, which stands as a hallmark for future all-spin information processing technologies. [ABSTRACT FROM AUTHOR]

The zigzag-type atomic structure at edges of graphenes theoretically produces flat energy band. Because electrons have infinite effective mass at the flat band, they localize at zigzag edges with high densities. The localized electron spins are spontaneously polarized due to mutual Coulomb interaction in spite of a material consisting of only carbon atom with sp2 bonds. However, in most experimental studies, spin polarization (such as ferromagnetism) has been observed in defect-related carbon systems. Here, we fabricate honeycomb-like arrays of low-defect hexagonal antidots (nanopores) terminated by hydrogen atoms on graphenes. They are prepared by a non-lithographic method using nanoporous alumina templates. We find large-magnitude ferromagnetism arising from polarized electron spins localizing at the zigzag antidot edges. Moreover, weak hysteresis loop in magnetoresistance and also spin pumping effect are found for perpendicular and parallel magnetic fields applied to the few-layer antidot lattices with larger inter-antidot space. These promise to be a realization of rare-element free magnets and also novel spintronic devices such as all-carbon spin transistors. [ABSTRACT FROM AUTHOR]

Spin-orbit coupling (SOC) related to the minority interface resonance states (IRSs) of Fe(001) has been evidenced in full-epitaxial Fe(001)/MgO/Fe magnetic tunnel junctions (MTJs) from magnetotransport experiments correlated to theoretical ab initio calculations. We show that the SOC effect strongly depends on the symmetry composition of the 1RS, which has been skillfully engineered via the interfacial chemical structure in the Fe(001)/MgO stack. The SOC scattering is enhanced between the majority Δ1) and minority Δ5 band near the Fermi level when presenting a Δ5 symmetry dominant 1RS at the Fe/MgO interface. Our results validate the interplay between SOC and IRSs, which gives further understanding of the mechanisms responsible for the tunneling anisotropic magnetoresistance and the large perpendicular magnetic anisotropy at the Fe/MgO interface. [ABSTRACT FROM AUTHOR]

We demonstrate that a giant spin Hall effect (SHE) can be induced by introducing a small amount of Bi impurities in Cu. Our analysis, based on a new three-dimensional finite element treatment of spin transport, shows that the sign of the SHE induced by the Bi impurities is negative and its spin Hall (SH) angle amounts to --0.24. Such a negative large SH angle in CuBi alloys can be explained by applying the resonant scattering model proposed by Feri and Levy [Phys. Rev. Lett. 106, 157208 (2011)] to 6p impurities. [ABSTRACT FROM AUTHOR]

Theoretically, the so-called zigzag edge of graphenes provides localized electrons due to the presence of flat energy bands near the Fermi level. Spin interaction makes the localized spins strongly polarized, yielding ferromagnetism. However, in most experimental studies, ferromagnetism has been observed in uncontrollable and complicated carbon-based systems. Here, we fabricate graphenes with honeycomblike arrays of hexagonal nanopores, which have a large ensemble of hydrogen-terminated and low-defect pore edges that are prepared by a nonlithographic method (nanoporous alumina templates). We observe large-magnitude ferromagnetism derived from electron spins localizing at the zigzag nanopore edges. This promises to be a realization of graphene magnets and novel spintronic devices. [ABSTRACT FROM AUTHOR]

We study spin-dependent transport theoretically in structures with a barrier composed of magnesium oxide and ferromagnetic electrodes with a noncollinear orientation of magnetizations in the ferromagnetic layers. We consider the effects of tunnel magnetoresistance and of the spin torque in the two-band s-d model using the Keldysh technique of nonequilibrium Green's functions with the s-d hybridization taken into account. We investigate the role of a chromium layer as an additional spin filter for s electrons and the possibility of increasing the effects of tunnel magnetoresistance and of the spin torque for the resonance tunneling in the five-layer structure Fe|Cr|Fe|MgO|Fe. [ABSTRACT FROM AUTHOR]

The charge and spin diffusion equations, taking into account spin-flip and spin-transfer torque, were numerically solved using a finite element method in complex noncollinear geometry with strongly inhomogeneous current flow. As an illustration, spin-dependent transport through a nonmagnetic nanoconstriction, separating two magnetic layers was investigated. Unexpected results such as vortices of spin-currents in the vicinity of the nanoconstriction were obtained. The angular variations of magnetoresistance and spin-transfer torque are strongly influenced by the structure geometry. [ABSTRACT FROM AUTHOR]

Abstract: We systemically studied the OH-terminated diamond (001) surfaces by first-principles calculations. A set of network structures are investigated, two of them are found to be energetically favored over a recently proposed anti-parallel configuration [S.J. Sque, R. Jones, P.B. Briddon, Phys. Rev. B 73 (2006) 085313]. The transition paths and barriers between the anti-parallel configuration and the network structures are calculated. Furthermore, using ab initio molecular dynamics, a scissor mode of pseudo-water molecules in vibrational spectra was found, which is in well agreement with available experiments. [Copyright &y& Elsevier]

Abstract: We report on the successful synthesis, magnetism and transport of highly spin-polarized chalcogenide thin films of CuCr2Se4, which are promising candidates for spin-based electronic applications. We also present electronic structure calculations for CuCr2Se4 that, together with magnetic and transport data, imply that the stoichiometric compound is a metallic ferromagnet with a relatively low density of hole-like carriers at the Fermi energy. These calculations also predict that a deficiency of Se will deplete the minority density of states at the Fermi energy perhaps leading to a half-metal. We have successfully grown thin films of CuCr2Se4 by pulsed laser deposition on isostructural MgAl2O4 substrates followed by an anneal in a Se-rich environment. X-ray diffraction confirms the structure of CuCr2Se4 on MgAl2O4 substrates as well as a secondary phase of Cr2Se3. X-ray absorption spectroscopy indicates that the chemical structure at the surface of the films is similar to that of bulk CuCr2Se4 single crystals. Magnetization measurements indicate that these films saturate with a magnetic moment close to 5 μ B/f.u. and a Curie temperature (T c) above 400K. X-ray magnetic circular dichroism measurements show that magnetic order persists to the surface of the film. Resistivity and Hall effect measurements are consistent with p-type ferromagnetic metallic behavior and with the electronic structure calculations. [Copyright &y& Elsevier]

The tunneling current for electrons tunneling between crystalline ferromagnetic electrodes through an epitaxial crystalline barrier can be calculated from first principles. These calculations show that the wave function symmetry can be exploited to achieve very high tunneling magnetoresistance. For the Fe(100)∣MgO(100) ∣Fe(100) system, the calculated conductance is much higher and its decrease with MgO thickness is much slower than has been estimated using a simple free electron-barrier model. [ABSTRACT FROM AUTHOR]

A quantum-statistical model using the Kubo formalism is proposed for describing the magnetoresistance of a multilayer structure with the current perpendicular to the plane of the layers. In particular, this model describes the case of noncollinear magnetization of consecutive ferromagnetic layers of the structure. Interference between electron wave functions with different directions of the spin projections onto the magnetization axis, which arises in the noncollinear configuration, is investigated along with the role of electron scattering, not only within the bulk of the layers, but also at their interfaces. [ABSTRACT FROM AUTHOR]

The so-called zigzag edge of graphenes theoretically has localized electrons due to the presence of flat energy bands near the Fermi level. The localized electron spins are strongly polarized, resulting in ferromagnetism. We fabricate graphenes with honeycomb-like arrays of hydrogen-terminated and low-defect hexagonal nanopores by a nonlithographic method using nanoporous alumina templates. We report large-magnitude room-temperature ferromagnetism caused by electron spins localizing at the zigzag nanopore edges. This promises to be a realization of rare-element free, controllable, transparent, flexible, and mono-atomic layer magnets and novel spintronic devices. [ABSTRACT FROM AUTHOR]

Room temperature transport properties are reported in polycrystalline SrTiO3-based magnetic tunnel junctions deposited by ion beam sputtering. The junctions comprise CoFeB electrodes and the SrTiO3 barrier with thickness varied between 0.9 and 1.9 nm. Resistance area product values between 3 Ω.μm2 and 22 kΩ.μm2 have been measured with a tunnel magnetoresistance ratio ranging from 3.1 to 13% at room temperature. At low barrier thickness (1.2 nm), ferromagnetic coupling between electrodes is observed, indicating the presence of defects in the structure. A post-oxidation step was found to improve transport properties at lower barrier thickness. [ABSTRACT FROM AUTHOR]

We present theoretical studies of the intrinsic spin-orbit torque (SOT) in a single-domain ferromagnetic layer with Rashba spin-orbit coupling (SOC) using the nonequilibrium Green's function formalism for a tight-binding Hamiltonian. We find that, in the case of a small electric field, the intrinsic SOT to first order in SOC has only the field-like torque symmetry and can be interpreted as the longitudinal spin current induced by the charge current and Rashba field. We analyze the results in terms of the material-related parameters of the electronic structure, such as the band filling, bandwidth, exchange splitting, and the Rashba SOC strength. On the basis of these numerical and analytical results, we discuss the magnitude and sign of SOT. Our results suggest that the different sign of SOT in identical ferromagnets with different supporting layers, e.g., Co/Pt and Co/Ta, can be attributed to electrostatic doping of the ferromagnetic layer by the support. [ABSTRACT FROM AUTHOR]

We present measurements of the spin Hall effect (SHE) in AuW and AuTa alloys for a large range of W or Ta concentrations by combining experiments on lateral spin valves and ferromagnetic-resonance/spin-pumping techniques. The main result is the identification of a large enhancement of the spin Hall angle (SHA) by the side-jump mechanism on Ta impurities, with a SHA as high as +0.5 (i.e., 50%) for about 10% of Ta. In contrast, the SHA in AuW does not exceed +0.15 and can be explained by intrinsic SHE of the alloy without significant extrinsic contribution from skew or side-jump scattering by W impurities. The AuTa alloys, as they combine a very large SHA with a moderate resistivity (smaller than 85μΩcm), are promising for spintronic devices exploiting the SHE. [ABSTRACT FROM AUTHOR]

Magnetoresistive and magnetoresonance measurements carried out on patterned perpendicular magnetic tunnel junction pillars and full-sheet films reveal magnetic inhomogeneities of FeCoB free layer grown on MgO and coated with Ta. At low FeCoB thicknesses, the layer behaves as an ensemble of weakly coupled grains resulting in a decrease of the free-layer thermal stability. In contrast, for thicker layers, the grains become more strongly coupled but strong magnetic inhomogeneities remain, yielding the emergence and further increase of a second-order magnetic anisotropy term (~K2effcos4θ), eventually resulting in an easy-cone anisotropy. We show that the static and dynamic magnetic properties of such a free layer can be successfully described by a granular model with three thickness-dependent parameters: mean perpendicular anisotropy of the grains, grain-to-grain anisotropy distribution, and intergrain exchangelike coupling strength. Easy-cone anisotropy may help reduce the stochasticity of the spin transfer torque switching. However, it arises at intermediate values of the intergrain exchange coupling where the spin transfer torque (STT) switching efficiency is degraded, as shown by multimacrospin modeling. This is due to the excitation of exchange modes contributing weakly to the STT switching process while dissipating part of the STT energy. [ABSTRACT FROM AUTHOR]

We present a theory of the anisotropy of tunneling magnetoresistance (ATMR) phenomenon in magnetic tunnel junctions (MTJs) attributed to Rashba spin-orbit interaction in the insulating barrier. ATMR represents the difference of tunnel magnetoresistance (TMR) amplitude measured with in-plane and out-of-plane magnetic configurations. It is demonstrated that within the spin-polarized free-electron model the change of conductance associated with the ATMR is exactly twice the change of conductance measured at full saturation (i.e., in parallel configuration of magnetizations) between in-plane and out-of-plane configuration, i.e., the tunneling anisotropic magnetoresistance (TAMR). Both ATMR and TAMR are closely related to the TMR amplitude and spin-orbit constant. The predicted ATMR phenomenon is confirmed experimentally, showing a few percent value in the case of the widely studied CoFeB/MgO/CoFeB based MTJ. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A correction to retract the article "Graphene magnet realized by hydrogenated graphene nanopore arrays" that was published online on March 1, 2012 is presented.