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Out-of-plane spin polarization {\sigma}_z has attracted increasing interests of researchers recently, due to its potential in high-density and low-power spintronic devices. Noncollinear antiferromagnet (AFM), which has unique 120{\deg} triangular spin configuration, has been discovered to possess {\sigma}_z. However, the physical origin of {\sigma}_z in noncollinear AFM is still not clear, and the external magnetic field-free switching of perpendicular magnetic layer using the corresponding {\sigma}_z has not been reported yet. Here, we use the cluster magnetic octupole in antiperovskite AFM Mn3SnN to demonstrate the generation of {\sigma}_z. {\sigma}_z is induced by the precession of carrier spins when currents flow through the cluster magnetic octupole, which also relies on the direction of the cluster magnetic octupole in conjunction with the applied current. With the aid of {\sigma}_z, current induced spin-orbit torque (SOT) switching of adjacent perpendicular ferromagnet is realized without external magnetic field. Our findings present a new perspective to the generation of out-of-plane spin polarizations via noncollinear AFM spin structure, and provide a potential path to realize ultrafast high-density applications., Comment: 23 pages, 4 figures, accepted by Nat. Commun

In this article, for the first time, we propose a silicene-based spin filter having a TFET configuration. The device portrays a voltage-dependent spin polarization and achieves a “spin polarization” as high as 98% at a minimal “operating voltage” (0.35 V). The operation of the device is based on the “spin-polarized edge states” in a silicene nanoribbon. The “spin polarization” of the output current can be tuned by modifying the bandgap of the spin-up and spin-down states via an in-plane perpendicular “electric field” generated by two “lateral gates.” The device features high spin polarization apart from its expected integration with Si-based technology. The proposed device has a simple construction, wherein a single layer of Si atoms achieves such a high value of spin polarization at a minimal operating voltage. The operation of the proposed device is demonstrated by using the first-principles quantum transport simulations.

The first-principle calculations of density functional theory were used to study the structural, electronic, magnetic, mechanic, and half-metallic behavior of Y2MnZ (Z = Al, Ga, In) within the spin generalized gradient approximation. These compounds can be experimentally synthesized due to their negative values of the calculated formation energies. Our calculations indicate that they are more stable in Cu2MnAl-type structure. The Hg2CuTi-type structure displays half-metallic characteristic with 100% spin polarization at the Fermi level. The value of calculated magnetic moment has an integer value of 2μB for Y2MnZ (Z = Al, Ga, In) in the Hg2CuTi-type structure which well matches with magnetic moments predicted from Slater–Pauling rule. Therefore, the Y2MnZ (Z = Al, Ga, In) in the Hg2CuTi-type structure is predicted to be a candidate for possible spintronics applications.

Electric field control of magnetic properties has been achieved across a number of different material systems. In diluted magnetic semiconductors (DMSs), ferromagnetic metals, multiferroics, etc., electrical manipulation of magnetism has been observed. Here, we study the effect of an electric field on the carrier spin polarization in DMSs ( GaAsMn ); in particular, emphasis is given to spin-dependent transport phenomena. In our system, the interaction between the carriers and the localized spins in the presence of electric field is taken as the main interaction. Our results show that the electric field plays a major role on the spin polarization of carriers in the system. This is important for spintronics application.

We theoretically investigate the dwell time for electrons in an antiparallel double $\delta $ -magnetic-barrier nanostructure, which is constructed on the surface of the InAs/Al x In1- x As heterostructure by patterning two ferromagnetic (FM) stripes. It is shown that the dwell time is dependent on electron spins due to the spin–field interaction between spins and magnetic fields. It is also shown that both magnitude and sign of the spin polarization in the dwell time can be modulated by the structural width or magnetic-strength difference between two magnetic barriers, which may give rise to a controllable temporal spin splitter for spintronics device applications.

To broaden the scope of van der Waals 2D magnets, we report the synthesis and magnetism of covalent 2D magnetic Cr$_2$Te$_3$ with a thickness down to one-unit-cell. The 2D Cr$_2$Te$_3$ crystals exhibit robust ferromagnetism with a Curie temperature of 180 K, a large perpendicular anisotropy of 7*105 J m-3, and a high coercivity of ~ 4.6 kG at 20 K. First-principles calculations further show a transition from canted to collinear ferromagnetism, a transition from perpendicular to in-plane anisotropy, and emergent half-metallic behavior in atomically-thin Cr$_2$Te$_3$, suggesting its potential application for injecting carriers with high spin polarization into spintronic devices.

The influence of spatial variation of Fermi velocity on the spin-polarized transport properties of massless Dirac fermions in proximity-induced ferromagnetic graphene junction was investigated. We found that the velocity ratio ξ causing the width of the spin conductance dip near the Dirac point is broadened as the Fermi velocity ratio increases. In contrast, the effect of the Fermi velocity mismatch does not affect the shifting of the Dirac point. It leads to the indirect measurement of the Fermi velocity ratio that can be tuned by the spin-dependent conductance. In addition to the presence of both the exchange field and the Fermi velocity modulation, we found high spin filtering occurs when the Fermi velocity ratio ξ ≥ 1. Due to the transmission probability of electron with spin down, T↓ is blocked by the effect of Fermi velocity modulation similar to waves travelling through a different media. Moreover, we also found that the resonant transmission of the electron with spin up can be perfectly transmitted through the Fermi velocity barrier at the limit injected angle θ → π/2 for H/EF ≈ 1. The spin transport properties can be controlled by suitably modifying the strength of the ferromagnetic insulator and varying the Fermi velocity modulation, which leads to the highest spin polarization. By manipulating the behavior of spin-dependent collimation and spin beam splitting in this structure, we proposed a spin transport device for making lateral spin polarization. These interesting features will help make the development of spintronic devices in the graphene-based nanostructure.

Silicene has attracted the research interest due to its excellent electronic and spin properties. Furthermore, CrO2 half metal due to its high Curie temperature and high spin polarization is well suited for electrodes. In this work, we have simulated the magnetic tunnel junction device consisting of CrO2 electrodes and Silicene as a scattering region. The device is in a sub 10-nm regime, hence supports high integration density. The bias dependent spin transport properties (I-V characteristics and transmission spectrum) of the modeled device were calculated by Atomistic Tool Kit software, which uses density functional theory and non-equilibrium Greens function formalism. The device shows large tunnel magnetoresistance of 640%, depicting the potential application of the proposed device. The spin-dependent transmission spectrum, band structure, semi-conductor theory has been discussed to explain the origin of the spin-dependent transport characteristics. Moreover, an efficient method for MRAM (magnetic random access memory) read/write operation has been discussed. Furthermore, a NAND gate from a single modeled MTJ device has been realized, a half adder has also been realized from the modeled device to explore the potential of the modeled device for the implementation of complex digital functions.

Due to the gapless between any two successive subbands with the same spin, the spin polarization in uniform MoS2 zigzag nanoribbon (MoS2-ZR) is weak. Here, through configuring Z-shaped structure, we realize 100% spin polarization in MoS2-ZR with only exchange field. The filtered spin electrons transmit along a specified edge of the device. This phenomenon is the result of the combined effect of the localized edge states and structure induced inversion of the Mo-edge and S-edge. In our calculation the fully spin polarization appears in several energy regions, so this Z-shaped MoS2-ZRs can be used in making spintronic devices.

Nodal-ring semimetals with band crossing are the new type of quantum materials that have attracted considerable interest from scholars for research. In general, the spin–orbit coupling (SOC) effect opens a band gap at the Dirac point. Therefore, finding 2D nodal-ring semimetals with resistance to SOC has more challenges. Based on first-principles calculations, we propose here that the two-dimensional (2D) Ta2C3 monolayer is a novel nodal-ring semimetal. In particular, Ta2C3 forms six closed rings in the Brillouin zone (BZ) with SOC, which originates from the dxy,x2–y2 orbitals of Ta and the pz orbitals of C. The nodal-ring bands at the K point in Ta2C3 exhibits characteristics of valley splitting and spin polarization due to the breaking of inversion symmetry and SOC. The masximal spin-splitting at the K point is as large as 268.87 meV and 61.90 meV for the conduction band minimum (CBM) and valence band maximum (VBM), respectively. The massless Dirac fermions in the non-equivalent valley have the opposite Berry curvature and spin moment. Therefore, 2D Ta2C3 is novel spin-valley-coupled nodal-ring semimetal. In addition, we found interesting negative differential resistance effects when calculating its transport properties. Our results not only provide an ideal platform for studying the combination of new physical properties, spintronics and valleytronics, but also open the way for designing low-power and fast-transport electronic devices.

The interconversion of charge and spin currents via spin-Hall effect is essential for spintronics. Energy-efficient and deterministic switching of magnetization can be achieved when spin polarizations of these spin currents are collinear with the magnetization. However, symmetry conditions generally restrict spin polarizations to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced. Here, we show control of the spin polarization direction by using a non-collinear antiferromagnet Mn3GaN, in which the triangular spin structure creates a low magnetic symmetry while maintaining a high crystalline symmetry. We demonstrate that epitaxial Mn3GaN/permalloy heterostructures can generate unconventional spin-orbit torques at room temperature corresponding to out-of-plane and Dresselhaus-like spin polarizations which are forbidden in any sample with two-fold rotational symmetry. Our results demonstrate an approach based on spin-structure design for controlling spin-orbit torque, enabling high-efficient antiferromagnetic spintronics., In the typical spin-hall effect, spin-current, charge current, and spin polarisation are all mutually perpendicular, a feature enforced by symmetry. Here, using an anti-ferromagnet with a triangular spin structure, the authors demonstrate a spin-hall effect without a perpendicular spin alignment.

Spin valves based on materials in which the spin-flip is suppressed by the spatial separation of charge carriers, while maintaining electric neutrality in the valve volume, are considered. The possibility of using these valves as electric batteries is discussed. It is shown that if the potential difference across the valve is controlled, incommensurability effects such as the "devil's staircase" may be expected, which are associated with the Coulomb interaction and redistribution of electrons occurring while the battery is charged and discharged. The effects of the emergence and vanishing of spontaneous spin polarization of conduction electrons with a change in the Fermi level in the valve are predicted. Such spin valves can also be used in implementing spintronic memory cells, supercapacitors, and similar devices.

2D intrinsic ferromagnets with high spin polarization and high Curie temperature are rare and very important for developing novel nanoscale spintronic materials and devices. In this letter, by usin...

The effects of lead positions and lead-ring coupling regimes are investigated for spin-related transport through a two-dimensional network of quantum nanorings (2DNQRs) considering Rashba spin–orbit interaction (RSOI) and magnetic flux. A matrix representation of the transmission and reflection coefficients through a single ring connected to the arbitrary number of leads has been introduced. As a specific example of 2DNQRs, the conductance, spin polarization and system efficiency are obtained via a triangular network of quantum rings (TNQRs). TNQRs are completely opaque or transparent versus RSOI strength and wave vector (k) of the incident electron. The periodicity of these functions along the k axis depends on the lead positions and is independent of lead-ring coupling. Also, the symmetric geometry and strong lead-ring coupling regime significantly improve the performance of the system as a multipurpose spintronic device (i.e., a perfect spin filter, spin splitter, spin switching, Stern–Gerlach device and an electronic switching device).

The effective spin polarization and spin filtering of a linear chain of N one-dimensional nanorings in the presence of the Rashba and Aharonov–Bohm effects are studied by considering three different lead–ring coupling regimes. Utilizing the transfer-matrix method, the optimal number of rings for maximizing the system efficiency is determined in the weak, medium, and strong lead–ring coupling regimes. The strong coupling regime is proposed for the design of spintronic devices as it exhibits the highest system efficiency. Furthermore, by tuning the Rashba strengths in the rings alternately, perfect spin filtering and full-range spin polarization with high efficiency can be obtained in narrow ranges of the incident electron wavenumber. Moreover, controlling the Rashba strength leads to the design of energy-filtering devices with a desired spin polarization, which could play a dominant role in spintronic technology.

Compared with the conventional magnetic means (such as ferromagnetic contacts), controlling a spin current by electrical methods could largely reduce the energy consumption and dimensions of nano-devices, which has become a focus of research in spintronics. Inspired by recent progress in the synthesis of an iron-based metal-organic nanostructure, we investigate the spin-dependent electronic transport of the molecule of Fe3-terpyridine-phenyl-phenyl-terpyridine-Fe3 (Fe3-TPPT-Fe3) through first-principles calculations, and propose a three-terminal device without ferromagnetics. By applying a gate voltage, not only the spin polarization can be switched between 100% and -100% to achieve a dual-spin filter, but also its fine regulation can be realized, where the transmission with any ratio of spin-up to spin-down electron numbers is achievable. Analysis shows that the particular transmission spectra are the key mechanism, where two peaks reside discretely on both sides of the Fermi level with opposite spins. Such a feature is found to be robust to the number of Fe atoms and TPPT chain length, suggesting that it is an intrinsic feature of such systems and very conducive to practical applications. The electrical control (such as an electric field) of spin polarization is realized at the single-molecule level, showing great application potential.

In this study, an experimentally synthesized DHM LaNiO3 is discovered with many Dirac cones and complete spin polarization near the Fermi level via first principles; it is also shown that the crystal structures of these materials are strongly correlated with their physical properties., In the past three years, Dirac half-metals (DHMs) have attracted considerable attention and become a high-profile topic in spintronics becuase of their excellent physical properties such as 100% spin polarization and massless Dirac fermions. Two-dimensional DHMs proposed recently have not yet been experimentally synthesized and thus remain theoretical. As a result, their characteristics cannot be experimentally confirmed. In addition, many theoretically predicted Dirac materials have only a single cone, resulting in a nonlinear electromagnetic response with insufficient intensity and inadequate transport carrier efficiency near the Fermi level. Therefore, after several attempts, we have focused on a novel class of DHMs with multiple Dirac crossings to address the above limitations. In particular, we direct our attention to three-dimensional bulk materials. In this study, the discovery via first principles of an experimentally synthesized DHM LaNiO3 with many Dirac cones and complete spin polarization near the Fermi level is reported. It is also shown that the crystal structures of these materials are strongly correlated with their physical properties. The results indicate that many rhombohedral materials with the general formula LnNiO3 (Ln = La, Ce, Nd, Pm, Gd, Tb, Dy, Ho, Er, Lu) in the space group R 3 c are potential DHMs with multiple Dirac cones.

Experiments on spin transport through a chiral molecule demonstrated the attainment of significant spin polarization, demanding a theoretical explanation. We report the emergence of spin Fano resonances as a mechanism in the chiral-induced spin-selectivity (CISS) effect associated with transport through a chiral polyacetylene molecule. Initializing electrons through optical excitation, we derive the Fano resonance formula for the spin polarization. Computations reveal that quasidegeneracy is common in this complex molecular system. A remarkable phenomenon is the generation of pronounced spin Fano resonances due to the contributions of two near-degeneracy states. We also find that the Fano resonance width increases linearly with the coupling strength between the molecule and the lead. Our findings provide another mechanism to explain the experimental observations and lead to new insights into the role of the CISS effect in complex molecules from the perspective of transport and spin polarization resonance, paving the way for chiral molecule-based spintronics applications.

The control of spin current is pivotal for spintronic applications, especially for spin-orbit torque devices. Spin Hall effect (SHE) is a prevalent method to generate spin current. However, it is difficult to manipulate its spin polarization in nonmagnet. Recently, the discovery of spin current in ferromagnet offers opportunity to realize the manipulation. In the present work, the spin current in van der Waals ferromagnet Fe3GeTe2 (FGT) with varying magnetization is theoretically investigated. It has been observed that the spin current in FGT presents the nonlinear behavior with respect to magnetization. The in-plane and out-of-plane spin polarization emerges simultaneously, and the bilayer FGT can even exhibit arbitrary spin polarization thanks to the reduced symmetry. More intriguingly, the correlation between anomalous Hall effect (AHE) and spin anomalous Hall effect (SAHE) has been interpreted from the aspect of Berry curvature. This work illustrates that the interplay of symmetry and magnetism can effectively control the magnitude and spin polarization of the spin current, providing a practical method to realize exotic spin-orbit torques.

We theoretically investigate spin polarization for electrons in magnetically and electrically confined semiconductor microstructure, which is constructed by patterning a ferromagnetic stripe and a Schottky-metal stripe on top and bottom of GaAs/AlxGa1-xAs heterostructure, respectively. Both Zeeman interaction and spin–orbit coupling are taken into account; however, electron-spin polarization comes mainly from the latter due to a small effective g-factor for GaAs. Besides, both magnitude and sign of spin polarization can be manipulated by changing interfacial confining electric field or strain engineering, resulting in a tunable electron-spin filter for spintronics device applications.

In this paper, we theoretically investigated the electronic properties of monolayer $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ by combining first-principles calculations and symmetry analyses. Spin-orbital coupling resulted in band splitting, whereas a horizontal mirror symmetry constrained the spin polarization to be along the $z$ direction. In addition, a three-band tight-binding model was constructed to describe the low-energy quasiparticle states of monolayer $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$, which can be generalized to strained $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ and its derivatives. The calculations using the tight-binding model showed an undamped $\sqrt{q}$-dependent plasmon mode, consistent with the results of first-principles calculations. The developed model is suitable for future theoretical and numerical investigations of low-energy properties in $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ family materials. Furthermore, the study of the electronic properties of monolayer $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ paves a way for its applications in spintronics and plasmonics.

Interconversion of charge and spin currents via spin Hall effect is one of the key physical phenomena in spintronics. However, the spin polarizations are orthogonal to both the charge and spin flows due to the restricted symmetry conditions. Here, we use noncollinear antiferromagnet ${\mathrm{Mn}}_{3}\mathrm{Pt}$, which has different magnetic mirror planes in different orientations, to investigate magnetic symmetry dependent atypical spin-orbit torques. We observed weak generation of out of plane spin polarization $({\ensuremath{\sigma}}_{z})$ in ${\mathrm{Mn}}_{3}\mathrm{Pt}$/permalloy bilayers when current was applied perpendicular to the magnetic mirror plane of ${\mathrm{Mn}}_{3}\mathrm{Pt}$, and strong generation of ${\ensuremath{\sigma}}_{z}$ when current was applied parallel to the magnetic mirror plane. All three oriented ${\mathrm{Mn}}_{3}\mathrm{Pt}$ films show the same pattern, indicating the generation of unconventional ${\ensuremath{\sigma}}_{z}$ has strong dependence on magnetic symmetry. Controlling spin-orbit torques by changing current directions in differently oriented ${\mathrm{Mn}}_{3}\mathrm{Pt}$ films provides a strategy for optimizing antiferromagnetic spintronics.

It is now well established that the peculiar linear-in-momentum dependence of the Rashba (and of the Dresselhaus) spin-orbit coupling leads to the vanishing of the spin Hall conductivity in the bulk of a two-dimensional electron gas (2DEG). In this paper we discuss how generic magnetic couplings change this behaviour providing then a potential handle on the spin Hall effect. In particular we examine the influence of magnetic impurities and an in-plane magnetic field. We find that in both cases there is a finite spin Hall effect and we provide explicit expressions for the spin Hall conductivity. The results can be obtained by means of the quasiclassical Green function approach, that we have recently extended to spin-orbit coupled electron systems.

International audience; Topological insulators (TI) have gained much interest in the field of spintronics for the generation of pure spin currents. Indeed, three-dimensional TIs are predicted to host exotic properties like topologically protected surface states (TSS), which show Dirac-like band dispersion and spin-momentum locking [1]. One of the main strategies is to take advantages of the spin polarization of the TSSs to manipulate the magnetization of an adjacent ferromagnetic thin film (FM) using the spin-orbit torque (SOT) mechanism [2]. In the past few years, the community attempted to replace the traditional heavy metals by a TI in order to enhance the SOT efficiency with limited success. It now appears that the interface sharpness and the high chemical affinity between Bi-based TIs and classical 3d FMs is a major hurdle to reach the predicted breakthrough in magnetization switching power-efficiency [3]. The emergence of ferromagnetism in two dimensions in 2017, which started a new field in condensed matter physics, could bring a solution to this issue.The van der Waals (vdW) nature of the interaction between the TI and the 2D-FM should limit chemical reactions, interface intermixing and hybridization of state between the two layers.

The behavior of spin for incoherently hopping carriers is critical to understand in a variety of systems such as organic semiconductors, amorphous semiconductors, and muon-implanted materials. This work specifically examined the spin relaxation of hopping spin/charge carriers through a cubic lattice in the presence of varying degrees of energy disorder when the carrier spin is treated classically and random spin rotations are suffered during the hopping process (to mimic spin–orbit coupling effects) instead of during the wait time period (which would be more appropriate for hyperfine coupling). The problem was studied under a variety of different assumptions regarding the hopping rates and the random local fields. In some cases, analytic solutions for the spin relaxation rate were obtained. In all the models, we found that exponentially distributed energy disorder led to a drastic reduction in spin polarization losses that fell nonexponentially.

The ability to engineer new states of matter and control their spintronic properties by electric fields is at the heart of future information technology. Here, we report a gate-tunable spin-galvanic effect in van der Waals heterostructures of graphene with a semimetal of molybdenum ditelluride at room temperature due to an efficient spin-charge conversion process. Measurements in different device geometries with control over the spin orientations exhibit spin-switch and Hanle spin precession behavior, confirming the spin origin of the signal. The control experiments with the pristine graphene channels do not show any such signals. We explain the experimental spin-galvanic signals by theoretical calculations considering the spin-orbit induced spin-splitting in the bands of the graphene in the heterostructure. The calculations also reveal an unusual spin texture in graphene heterostructure with an anisotropic out-of-plane and in-plane spin polarization. These findings open opportunities to utilize graphene-based heterostructures for gate-controlled spintronic devices.

A novel spin gapless semiconductor material Ba2MnTeO6 is found and reported by first-principles calculations. In this paper, we study the influence of spin orbit coupling, strain and Coulomb interaction on the properties of ferromagnetic Ba2MnTeO6 in order to test the stability of physical properties. It turns out that the spin orbit coupling has no significant effect on the electronic structures of the Ba2MnTeO6 at equilibrium state. Under the action of uniform compressive strain and tensile strain, Ba2MnTeO6 transforms from spin gapless semiconductor to semiconductor and half-metal respectively. At the same time, as the strain increases, the semiconductor band gap gradually widens, and the half-metallic gap gradually narrows. After considering Coulomb interaction, Ba2MnTeO6 will also be transformed into a semiconductor, and the semiconductor band gap will increase with the increasing of U values. Furthermore, the mechanical performance studies show that Ba2MnTeO6 is an anisotropic material with stable structure. As the first pure double perovskite type spin gapless semiconductor, the high spin polarization and accurately adjustable physical properties of ferromagnetic Ba2MnTeO6 indicate that it has broad application prospects in the fields of spintronics and optoelectronic materials and devices.

Manipulating electron spins on ultrashort timescales shows promise in the field of data processing. Because of the direct electron-photon coupling, photons have been widely used for such studies, but not phonons. Here we tie coherent phonon detection to transient spin populations. We optically excite gigahertz picosecond phonon wave packets in a metal-coated GaAs slab containing $\mathrm{GaAs}\text{/}{\mathrm{Al}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{As}$ multiple quantum wells on the opposite side. Before the phonon wave-packet arrival, circularly polarized light induces a transient spin polarization. Phonon-induced ultrafast polarization rotation and reflectivity changes contingent on the transient spin population are detected by a heterodyne modulation technique. With an analytical model, we posit the presence of significant second-order interactions, enabled by spins, in the coherent-phonon optical detection. Applications include transient spin population monitoring and novel spintronic nanodevices.

All-electric magnetization manipulation at low power is a prerequisite for a wide adoption of spintronic devices. Materials such as heavy metals1–3 or topological insulators4,5 provide good charge-to-spin conversion efficiencies. They enable magnetization switching in heterostructures with either metallic ferromagnets or with magnetic insulators. Recent work suggests a pronounced Edelstein effect in Weyl semimetals due to their non-trivial band structure6,7; the Edelstein effect can be one order of magnitude stronger than it is in topological insulators or Rashba systems. Furthermore, the strong intrinsic spin Hall effect from the bulk states in Weyl semimetals can contribute to the spin current generation8. The Td phase of the Weyl semimetal WTe2 (WTe2 hereafter) possesses strong spin–orbit coupling6,9 and non-trivial band structures10 with a large spin polarization protected by time-reversal symmetry in both the surface and bulk states9–11. Atomically flat surfaces, which can be produced with high quality12, facilitate spintronic device applications. Here, we use WTe2 as a spin current source in WTe2/Ni81Fe19 (Py) heterostructures. We report field-free current-induced magnetization switching at room temperature. A charge current density of ~2.96 × 105 A cm−2 suffices to switch the magnetization of the Py layer. With the charge current along the b axis of the WTe2 layer, the thickness-dependent charge-to-spin conversion efficiency reaches 0.51 at 6–7 GHz. At the WTe2/Py interface, a Dzyaloshinskii–Moriya interaction (DMI) with a DMI constant of −1.78 ± 0.06 mJ m−2 induces chiral domain wall tilting. Our study demonstrates the capability of WTe2 to efficiently manipulate magnetization and sheds light on the role of the interface in Weyl semimetal/magnet heterostructures. The Weyl semimetal WTe2 possesses strong spin–orbit coupling and time-reversal-protected spin polarization in surface and bulk states. In a WTe2/permalloy heterostructure, WTe2 can act as a spin current source that enables magnetization switching at low current densities.

We study the spin transport in bilayer graphene nanoribbons (BGNs) in the presence of Rashba spin-orbit interaction (SOI) and external gate voltages. It is found that the spin polarization can be significantly enhanced by the interlayer asymmetry or longitudinal mirror asymmetry produced by external gate voltages. Rashba SOI alone in BGNs can only generate current with spin polarization along the in-plane y direction, but the polarization components can be found along the x, y and z directions when a gate voltage is applied. High spin polarization with flexible orientation is obtained in the proposed device. Our findings shed new light on the generation of highly spin-polarized current in BGNs without external magnetic fields, which could have useful applications in spintronics device design.

In recent years, the search for new Dirac half-metallic materials has been one of the hotspots in the field of spintronics because they have very good physical properties, such as massless Dirac fermions and full spin polarization. In this study, using density function theory combined with the quasi-harmonic Debye model, we show that perovskite-type dysprosium manganite is a novel half metal with multiple Dirac cones. A detailed study of the electronic, magnetic, and thermodynamic properties of DyMnO3 was carried out. Furthermore, the effects of uniform strain, the on-site Coulomb interaction U, spin-orbit coupling, and hole and electron doping on the multiple Dirac cones and full spin polarization were investigated. We should point out that such a spin-polarized Dirac material is rare among perovskite-type compounds. Hence, we hope that, through this work, this kind of material will receive more extensive attention in future studies.

This work presents a theoretical investigation on the electronic properties of double atomic carbon chains bridging graphene electrodes with density functional theory in combination with non-equilibrium Green's function. The influence of strain on the conductance of atomic carbon chains is significant. However, the coupling effect between adjacent chains dominates the intrinsic transport of double atomic carbon chains. For the coupled double atomic chains, the electron conductance of even-numbered atomic chains is significantly enhanced, while the electron conductance of odd-numbered atomic chains decreases to a certain degree, and the dependence of the conductance of double atomic chains on electrode configuration is stronger than the corresponding single atomic chain. More intriguingly, the coupled double atomic chains exhibit excellent spin-filtering properties with antiparallel spins on two electrodes. The current spin polarization stems from the coupling-induced changes of electron density and band offset reaches 100%. The coupled double atomic carbon chains have great potential application in spintronic devices and carbon-based field-effect transistors.

The development of materials that are non-magnetic in the bulk but exhibit two-dimensional (2D) magnetism at the surface is at the core of spintronics applications. Here, we present the valence-fluctuating material EuIrSi, where in contrast to its non-magnetic bulk, the Si-terminated surface reveals controllable 2D ferromagnetism. Close to the surface the Eu ions prefer a magnetic divalent configuration and their large 4f moments order below 48 K. The emerging exchange interaction modifies the spin polarization of the 2D surface electrons originally induced by the strong Rashba effect. The temperature-dependent mixed valence of the bulk allows to tune the energy and momentum size of the projected band gaps to which the 2D electrons are confined. This gives an additional degree of freedom to handle spin-polarized electrons at the surface. Our findings disclose valence-fluctuating rare-earth based materials as a very promising basis for the development of systems with controllable 2D magnetic properties which is of interest both for fundamental science and applications., This work was supported by the German Research Foundation (DFG) through Grants No. KR3831/5-1, No. LA655/20-1 and Fermi-NEst. Support was provided by the Spanish Ministry of Science, Innovation and Universities (Project No. FIS2016-76617-P and No. FIS2016-75862-P). We acknowledge financial support from the Spanish Ministry of Economy (MAT-2017-88374-P). The authors also acknowledge support by Saint Petersburg State University (Grant No. 15.61.202.2015) and Tomsk State University Academic D. I. Mendeleev Fund Program (Research Grant No. 8.1.01.2018). We acknowledge Diamond Light Source for access to beamline I05 (proposals no. SI18844-1 and SI17761-1) that contributed to the results presented here.

The 1-D nanoscale structures are studied with a potential relief containing magnetic barriers separated by nonmagnetic quantum wells in the absence of exchange interaction between the magnetic moments of adjacent barriers. The considered structure is the sequence of N barriers divided into two “ferromagnetic domains” of the length n and N - n-1, both having parallel internal fields. In contrast, the internal field of the nth barrier is not coplanar with respect to the internal fields of the left and/or right “domains.” The degree of spin polarization of an electron wave transmitted through this system is calculated with the assumption that the incident wave is unpolarized with the degree of its polarization equals zero. It is shown that the degree of polarization of the transmitted wave as a function of the impulse exhibits a sequence of sufficiently wide plateaus, which are close to unity. In particular, there are significant deviations from the known spintronics phenomena found earlier in this system such as the valve, filter, and giant magnetoresistance effects. This circumstance provides opportunities for managing the transport properties of the system by varying the noncoplanar degrees of freedom of the system.

In this work, the spin-resolved transport properties of the Fe doped SnS2 monolayer devices have been investigated. The results show that the doping systems have the transport properties of negative differential resistance, large magnetoresistance effect and near 100% spin polarization effect when the magnetization directions of two electrodes are in parallel. Moreover, the mechanisms for the properties also have been discussed. The original reason of these results could be due to the half-metallic of the doping system. Our results imply that Fe doped SnS2 monolayer is a promising candidate for the future spintronic devices.

The realization of robust intrinsic ferromagnetism in two-dimensional (2D) materials in conjunction with the intriguing quantum anomalous Hall (QAH) effect has provided a fertile ground for novel physics and for the next-generation spintronic and topological devices. On the basis of density functional theory (DFT), we predict that layered 5d transition-metal heavier halides (TMHs), such as ReX3 (X = Br, I), show intrinsic ferromagnetism with high spin polarization and high Curie temperatures. The outstanding dynamic and thermodynamic stability ensures their experimental feasibility. The strong spin-orbit coupling (SOC) of Re makes the electronic structure of the ReI3 monolayer topologically nontrivial with a large Chern number (C = -4). DFT+U calculations reveal that the 2D system undergoes a nontrivial to trivial transition with increasing on-site Hubbard Coulomb interaction U through the emergence of a Dirac cone. This transition is corroborated by the emergence of chiral edge states and the anomalous Hall conductivity. These findings not only demonstrate room-temperature ferromagnetism in atomically thin 5d TMHs, but also pave the way for the potential realization of the QAH effect with high Chern numbers in pristine 2D layers.

Spin transport properties in a non-uniform quantum wire (QW) in the presence of both the Rashba and Dresselhaus spin–orbit couplings (SOCs) is investigated by using the non-equilibrium Green's function (NEGF) method combined with the Landauer Buttiker formalism. It is found that such a non-uniform quantum wire exhibits considerable spin polarization in its conductance in the influence of both the Rashba and Dresselhaus SOCs, and that the two SOCs' strengths strongly affect both the magnitude and sign of the electron spin polarization. Interestingly, the Rashba and Dresselhaus SOCs play the same modulating role in the electron spin polarization. The proposed nanostructure can potentially be utilized to devise an all-electrical spintronic device.

Spin-transfer torque (STT) and spin-orbit torque (SOT) are spintronic phenomena allowing magnetization manipulation using electrical currents. Beyond their fundamental interest, they allow developing new classes of magnetic memories and logic devices, in particular based on domain wall (DW) motion. In this work, we report the study of STT driven DW motion in ferrimagnetic manganese nickel nitride (Mn4-xNixN) films, in which a fine adjustment of the Ni content allows setting the magnetic compensation at room temperature. The reduced magnetization, combined with the large spin polarization of conduction electrons, strongly enhances the STT so that domain wall velocities approaching 3000 m/s can be obtained for Ni compositions close to the compensation point. In addition, a reversal of the domain wall motion direction is observed when the magnetic compensation composition is crossed. This striking feature, related to the change of direction of the spin polarization with respect to that of the net magnetization, is clarified by ab initio band structure calculations., Comment: 24 pages, 4 figures

The observation of in-plane ferromagnetism in layered magnetic materials in conjunction with the topological nodal-ring dispersion in a spin gapless semimetal with 100 % spin polarization has a fertile ground for novel physics, rich scientific significance and for the next-generation advanced spintronic and topological devices. Topological nodal ring spin gapless semimetals with large band gap in the other spin channel prevents the spin leakage and are excellent spintronic materials. On the basis of density functional theory (DFT), we have studied the layered magnetic perovskite, CsMnF4 which is predicted to be a ferromagnetic insulator though the fellow compounds like AMnF4 (A = Na, K, Rb) are anti-ferromagnetic in nature. DFT + U calculations reveal that this layered system undergoes a transition from an insulating to half-semimetallic nature with decreasing on-site Hubbard Coulomb interaction, U. For U = 2.5 eV, we observe the topological nature in the system with the emergence of four Mexican hat like dispersions associated with band-flipping. Also, we calculated the magneto-crystalline anisotropic energy with inclusion of spin-orbit coupling (SOC) and found that the system consists of in-plane ferromagnetism. Transport properties infer huge anisotropy of one order of magnitude between 'a' and 'c' axes. Interestingly, the estimated Fermi velocities are 2.66 × 105 and 2.24 × 105 m s-1 for Z(=0) and Z(=0.5) plane respectively and are comparable to that of graphene, which might fetch applications in high speed spin electronic devices. The topological phase observed is robust to SOC and the band-crossings associated with nodal rings could be preserved by additional symmetry as the time-reversal symmetry breaks in magnetic systems. The nearly charge compensation observed from Fermi surfaces might fetch memory device applications.

Some of the most promising materials for application in molecular electronics and spintronics are based on diradical chains. Herein, the proposed relation between increasing conductance with length and diradical character is revisited using ab initio methods that account for the static electron correlation effects. Electron transmission was previously obtained from restricted single determinant wavefuntions or tight-binding approximations, which are unable to account for static correlation. Broken Symmetry Unrestricted Kohn–Sham Density Functional Theory (BS-UKS-DFT) in combination with electron transport analysis based on electron deformation orbitals (EDOs) reflects an exponential decay of the electrical conductance with length. Also, other important effects such as quantum interference are correctly accounted for, leading to a decrease of the conductance as the diradical character increases. As a proof-of-concept, the electrical conductance obtained from BS-UKS-DFT and CASSCF(2,2) wavefunctions were compared in diradical graphene strips in the frame of the pseudo-π approach, obtaining very similar results.

The spin polarization in nonmagnetic materials is conventionally attributed to the outcome of spin-orbit coupling when the global inversion symmetry is broken. The recently discovered hidden spin polarization indicates that a specific atomic site asymmetry could also induce measurable spin polarization, leading to a paradigm shift in research on centrosymmetric crystals for potential spintronic applications. Here, combining spin- and angle-resolved photoemission spectroscopy and theoretical calculations, we report distinct spin-momentum-layer locking phenomena in a centrosymmetric, layered material, BiOI. The measured spin is highly polarized along the Brillouin zone boundary, while the same effect almost vanishes around the zone center due to its nonsymmorphic crystal structure. Our work demonstrates the existence of momentum-dependent hidden spin polarization and uncovers the microscopic mechanism of spin, momentum, and layer locking to each other, thus shedding light on the design metrics for future spintronic materials.

In a metal, electron interactions can cause a perfect spin polarization of the Fermi surface. For such a phase, only half of the noninteracting Fermi surface is available, and thus this state is commonly referred to as a ``half metal.'' Here we argue that in multiband electronic systems with nesting, further ``fractionalization'' of the Fermi surface is possible. Taking the AA bilayer graphene as a convenient test case, we demonstrate that under suitable conditions imposed on the electron interactions, doped AA bilayer graphene can host a ``quarter-metal'' phase. Its Fermi surface (Fermi contour) is simultaneously polarized relative to spin-related and valley-related operators. The resultant state is nematic and possesses peculiar transport properties: the electric current carries both valley-related and spin-related quanta. In addition, since the two polarizations can be controlled independently of each other, the quarter metal is a promising candidate for spintronics and valleytronics applications. Other types of Fermi-surface fractionalization are also discussed.

Spin-dependent photogalvanic effect (PGE) in low-dimensional magnetic systems has recently attracted intensive attention. Based on first-principle transport calculations and symmetry analyses, we propose a robust scheme to generate pure spin current by PGE in centrosymmetric materials with spin polarization antisymmetry. As a demonstration, the idea is successfully applied to a photoelectric device constructed with a zigzag graphene nanoribbon (ZGNR), which has intrinsic antiferromagnetic coupling between the two edges and spin degenerate band structure. It suggests that spin splitting is not a prerequisite for pure spin current generation. More interestingly, by further introducing external transverse electric fields to the two leads to lift the spin degeneracy, the device may behave multifunctionally, capable of producing fully spin-polarized current or pure spin current, depending on whether the fields in the two leads are parallel or antiparallel. Very importantly, our scheme of pure spin current generation with PGE is not limited to ZGNR and can be extended to other two-dimensional (2D) centrosymmetric magnetic materials with spin polarization antisymmetry, suggesting a promising category of 2D platforms for PGE-based pure spin current generation.

It has been generally accepted that the spin-orbit coupling effect in noncentrosymmetric materials leads to the band splitting and nontrivial spin polarization in the momentum space. However, in some cases, zero net spin polarization in the split bands may occurs, dubbed as the band splitting with vanishing spin polarization (BSVSP) effect, protected by non-pseudo-polar point group symmetry of the wave vector in the first Brillouin zone [K. Liu et al., Nat. Commun. 10, 5144 (2019)]. In this paper, by using first-principles calculations, we show that the BSVSP effect emerges in two-dimensional (2D) nonsymmorphic $\mathrm{Ga}XY$ ($X$= Se, Te; $Y$= Cl, Br, I) family, a new class of 2D materials having in-plane ferroelectricity. Taking the GaTeCl monolayer as a representative example, we observe the BSVSP effect in the split bands along the $X\text{\ensuremath{-}}M$ line located in the proximity of the conduction band minimum. By using the $\stackrel{P\vec}{k}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{P\vec}{p}$ Hamiltonian derived based on the symmetry analysis, we clarify that such an effect originates from the cancellation of the local spin polarization, enforced by non-pseudo-polar ${C}_{2v}$ point group symmetry of the wave vector along the $X\text{\ensuremath{-}}M$ line. Importantly, we find that the spin polarization can be effectively induced by applying an external out-of-plane electric field, indicating that an electrically tunable spin polarization for spintronic applications is plausible.

The complex oxide heterostructures such as LaAlO3/SrTiO3 (LAO/STO) interface are paradigmatic platforms to explore emerging multi-degrees of freedom coupling and the associated exotic phenomena. In this study, we reveal the effects of multiorbital and magnetic ordering on Rashba spin-orbit coupling (SOC) at the LAO/STO (001) interface. Based on first-principles calculations, we show that the Rashba spin splitting near the conduction band edge can be tuned substantially by the interfacial insulator-metal transition due to the multiorbital effect of the lowest t_2g bands. We further unravel a competition between Rashba SOC and intrinsic magnetism, in which the Rashba SOC induced spin polarization is suppressed by the interfacial magnetic ordering. These results deepen our understanding of intricate electronic and magnetic reconstruction at the perovskite oxide interfaces and shed light on the engineering of oxide heterostructures for all-oxides-based spintronic devices., 24 pages, 4 figures

One of the most fundamental and exotic properties of three-dimensional (3D) topological insulators (TIs) is spin-momentum locking (SML) of their topological surface states (TSSs), promising for potential applications in future spintronics. However, other possible conduction channels, such as a trivial two-dimensional electron gas (2DEG) with strong Rashba-type spin-orbit interaction (SOI) and bulk-conducting states that may possess a spin Hall effect (SHE), can coexist in 3D TIs, making determining the origin of the current-induced spin polarization (CISP) difficult. In this work, we directly compared the CISP between bulk-insulating ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{2}\mathrm{Se}$ (BTS221) and bulk-metallic ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ thin flakes using spin potentiometry. In the bulk-insulating BTS221, the observed CISP has a sign consistent with the expected helicity of the SML of the TSS, but an opposite sign to its calculated bulk spin Hall conductivity. However, compared to BTS221, an opposite CISP is observed in the bulk-metallic ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, consistent with both the expectations of its Rashba-Edelstein effect of the band-bending induced 2DEG and bulk intrinsic spin Hall Effect (SHE). If one assumes a representative occupation of the Rashba band of $3\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ with a relevant relaxation time of 100 fs, the contribution to the CISP could be more dominated by the bulk intrinsic SHE. Our results provide an electrical way to distinguish the TSS from other possible conducting channels in spin transport measurements on 3D TIs, and open ways for the potential applications in charge-spin conversion devices.

Transition metal dichalcogenides (TMDs) combine interesting optical and spintronic properties in an atomically-thin material, where the light polarization can be used to control the spin and valley degrees-of-freedom for the development of novel opto-spintronic devices. These promising properties emerge due to their large spin-orbit coupling in combination with their crystal symmetries. Here, we provide simple symmetry arguments in a group-theory approach to unveil the symmetry-allowed spin scattering mechanisms, and indicate how one can use these concepts towards an external control of the spin lifetime. We perform this analysis for both monolayer (inversion asymmetric) and bilayer (inversion symmetric) crystals, indicating the different mechanisms that play a role in these systems. We show that, in monolayer TMDs, electrons and holes transform fundamentally differently -- leading to distinct spin-scattering processes. We find that one of the electronic states in the conduction band is partially protected by time-reversal symmetry, indicating a longer spin lifetime for that state. In bilayer and bulk TMDs, a hidden spin-polarization can exist within each layer despite the presence of global inversion symmetry. We show that this feature enables control of the interlayer spin-flipping scattering processes via an out-of-plane electric field, providing a mechanism for electrical control of the spin lifetime., Comment: 9 pages, 3 figures

Two-dimensional (2D) intrinsic magnetic materials with high Curie temperature (Tc) coexisting with 100% spin-polarization are highly desirable for realizing promising spintronic devices. In the present work, the intrinsic magnetism of monolayer square CrBr2 is predicted by using first-principles calculations. The monolayer CrBr2 is an intrinsic ferromagnetic (FM) half-metal with the half-metallic gap of 1.58 eV. Monte Carlo simulations based on the Heisenberg model estimates Tc as 212 K. Furthermore, the large compressive strain makes CrBr2 undergo ferromagnetic-antiferromagnetic phase transition, when the biaxial tensile strain larger than 9.3% leads to the emergence of semiconducting electronic structures. Our results show that the intrinsic half-metal with a high Tc and controllable magnetic properties endow monolayer square CrBr2 a potential material for spintronic applications., Comment: 5 pages, 5 figures

Magnetism of graphene can be created by atomic defects, either hydrogen adsorption or single-carbon vacancy formation, owing to the unpaired $\ensuremath{\pi}$ electrons around the defects. Here we explore, based on rigorous first principles calculations, the possibility of voltage manipulation of two such types of $\ensuremath{\pi}$ magnetism in graphene via a scanning tunneling microscope tip. We find a remarkably different behavior. For the hydrogen, the magnetic moment can be switched on and off with voltage-induced doping, whereas, for the carbon vacancy, the spin splitting of the $\ensuremath{\pi}$ bands persists, almost independent of the extent of doping, due to the coupling between the $\ensuremath{\pi}$ and the $\ensuremath{\sigma}$ bonds. Furthermore, the local atomic structures near the vacancy can be reversibly manipulated by a coordination mechanism between an intermediate tip-defect distance and a moderate tip voltage, consequently leading to the reversal of spin polarization of the $\ensuremath{\pi}$ bands. Voltage control of the local magnetic states may open a new avenue for potential applications in spintronics.