Crystalline-Dependent Magnon Torques in All-Sputtered Hf/Cr2O3/Ferromagnet Heterostructures

Electron motion in spin-orbit torque devices inevitably leads to the Joule heating issue. Magnon torques can potentially circumvent this issue, as it enables the transport of spin angular momentum in insulating magnetic materials. In this work, a sandwich structure composed of Hf/antiferromagnetic Cr2O3/ferromagnet is fabricated and demonstrates that the magnon torque is strongly dependent on the crystalline structure of Cr2O3. Magnon torques are stronger when the Néel vector of Cr2O3 aligns parallel to the spin polarization generated in Hf, while they are suppressed when the Néel vector is perpendicular to the spin polarization. The magnon torque efficiency is estimated to be -0.134 using in-plane second harmonic Hall measurements. Using magnon torques, perpendicular magnetization switching of CoFeB is achieved, with a critical switching current density of 4.09 × 107 A cm-2. Furthermore, the spin angular momentum loss due to the insertion of Cr2O3 is found to be lower than that of polycrystalline NiO. The work highlights the role of antiferromagnet crystalline structures in controlling magnon torques, broadening the potential applications of magnon torques.

Observation of Thickness-Modulated Out-of-Plane Spin-Orbit Torque in Polycrystalline Few-Layer Td-WTe2 Film

The low-symmetry Weyl semimetallic Td-phase WTe2 exhibits both a distinct out-of-plane damping torque (τDL) and exceptional charge-spin interconversion efficiency enabled by strong spin-orbit coupling, positioning it as a prime candidate for spin-orbit torque (SOT) applications in two-dimensional transition metal dichalcogenides. Herein, we report on thickness-dependent unconventional out-of-plane τDL in chemically vapor-deposited (CVD) polycrystalline Td-WTe2 (t)/Ni80Fe20/MgO/Ti (Td-WTN-t) heterostructures. Angle-resolved spin-torque ferromagnetic resonance measurements on the Td-WTN-12 structure showed significant spin Hall conductivities of σSH,y = 4.93 × 103 (ℏ/2e) Ω-1m-1 and σSH,z = 0.81 × 103 (ℏ/2e) Ω-1m-1, highlighting its potential for wafer-scale spin-orbit torque device applications. Additionally, a detailed examination of magnetotransport properties in polycrystalline few-layer Td-WTe2 films as a function of thickness revealed a marked amplification of the out-of-plane magnetoresistance, which can be ascribed to the anisotropic nature of charge carrier scattering mechanisms within the material. Spin pumping measurements in Td-WTN-t heterostructures further revealed thickness-dependent spin transport properties of Td-WTe2, with damping analysis yielding an out-of-plane spin diffusion length of λSD ≈ 14 nm.

Tunable chiral magneto-transport through band structure engineering in magnetic topological insulators Mn(Bi1-xSbx)2Te4

Berry curvature and spin texture are representative tuning parameters that govern spin-orbit coupling-related physics and are also the foundation for future device applications. Here, we investigate the impact of the Sb-to-Bi ratio on shaping the electronic band structure and its correlated first- and second-harmonic magneto-transport signals in the intrinsic magnetic topological insulator Mn(Bi1-xSbx)2Te4. First-principles calculations reveal that the introduction of Sb not only triggers a topological phase transition but also changes the integral of the Berry curvature at the shifted Fermi level, which leads to the reversal of the anomalous Hall resistance polarity for Sb fractions x > 0.67. Moreover, it also induces the opposite spin splitting of the valence bands compared to the Sb-free host, and the resulting clockwise/counterclockwise spin chirality gives rise to a tunable unidirectional second-harmonic anomalous Hall response. Our findings pave the way for constructing chiral spin-orbitronic devices through band structure engineering.

Large Spin-Orbit Torque with Multi-Directional Spin Components in Ni4W

Spin-orbit torque (SOT) offers an efficient mechanism for manipulating the magnetization of ferromagnetic materials in spintronics-based memory and logic devices. However, conventional SOT materials, such as heavy metals and topological insulators, are limited by high crystal symmetry to generating and injecting only in-plane spins into the ferromagnet. Low-symmetry materials and symmetry-breaking strategies have been employed to generate unconventional spin currents with out-of-plane spin polarization, enabling field-free deterministic switching of perpendicular magnetization. Despite this progress, the SOT efficiency of these materials has typically remained low. Here, a large SOT efficiency of 0.3 in the bulk Ni4W at room temperature is reported, as evaluated by second harmonic Hall measurements. In addition, due to the low crystal symmetry of Ni4W, unconventional SOT from the out-of-plane and Dresselhaus-like spin components are observed. Notably, a large SOT efficiency of 0.73 is observed in W/Ni4W (5 nm), potentially resulting from additional interfacial contributions or extrinsic effects. Furthermore, field-free switching of perpendicular magnetization has been achieved using the multi-directional SOT of Ni4W, highlighting its potential as a low-symmetry SOT material for energy-efficient spintronic devices.

Nanometer-thick Si/Al gradient materials for spin torque generation

Green materials for efficient charge-to-spin conversion are desired for common spintronic applications. Recent studies have documented the efficient generation of spin torque using spin-orbit interactions (SOIs); however, SOI use relies on the employment of rare metals such as platinum. Here, we demonstrate that a nanometer-thick gradient from silicon to aluminum, which consists of readily available elements from earth resources, can produce a spin torque as large as that of platinum despite the weak SOI of these compositions. The spin torque efficiency can be improved by decreasing the thickness of the gradient, while a sharp interface was not found to increase the spin torque. Moreover, the electric conductivity of the gradient material can be up to twice as large as that of platinum, which provides a way to reduce Joule heating losses in spintronic devices.

Current-Driven Collective Control of Helical Spin Texture in van der Waals Antiferromagnet

Electrical control of quantum magnetic states is essential in spintronic science. Initial studies on the ferromagnetic state control were extended to collinear antiferromagnets and, more recently, noncollinear antiferromagnets. However, electrical control mechanisms of such exotic magnetic states remain poorly understood. Here, we report the first experimental and theoretical example of the current control of helical antiferromagnets, arising from the competition between collinear antiferromagnetic exchange and interlayer Dzyaloshinskii-Moriya interaction in new van der Waals (vdW) material Ni_{1/3}NbS_{2}. Due to the intrinsic broken inversion symmetry, an in-plane current generates spin-orbit torque that, in turn, interacts directly with the helical antiferromagnetic order. Our theoretical analyses indicate that a weak ferromagnetic order coexists due to the Dzyaloshinskii-Moriya interaction, mediating the spin-orbit torque to collectively rotate the helical antiferromagnetic order. Our Ni_{1/3}NbS_{2} nanodevice experiments produce current-dependent resistance change consistent with the theoretical prediction. This Letter widens our understanding of the electrical control of helical antiferromagnets and promotes vdW quantum magnets as interesting material platforms for electrical control.

Field-Free Perpendicular Magnetization Switching Through Topological Surface State in Type-II Dirac Semimetal Pt3Sn

Spin-orbit torque (SOT) induced by current is a promising approach for electrical manipulation of magnetization in advancing next-generation memory and logic technologies. Conventional SOT-driven perpendicular magnetization switching typically requires an external magnetic field for symmetry breaking, limiting practical applications. Recent research has focused on achieving field-free switching through out-of-plane SOT, with the key challenge being the exploration of new spin source materials that can generate z-polarized spins with high charge-to-spin conversion efficiency, structural simplicity, and scalability for large-scale production. This study demonstrates field-free perpendicular switching using an ultrathin type-II Dirac semimetal Pt3Sn layer with a topological surface state. Density functional theory calculations reveal that the unconventional SOT originates from a spin texture with C3v symmetry, leading to significant z-polarized spin accumulation in the Pt3Sn (111) surface, enabling the deterministic switching of perpendicular magnetization. These results highlight the potential of Dirac semimetals like Pt3Sn as scalable and efficient spin sources, facilitating the development of low-power, high-density spintronic memory and logic devices.

Electrical Manipulation of Field-Free Magnetization Switching Driven by Spin-Orbit Torque in Amorphous Gradient-Mn3Sn

Switching the magnetization without an assisted magnetic field is crucial for the application of spin-orbit torque (SOT) devices. However, the realization of field-free magnetization switching usually calls for intricate design and growth of heterostructure. In this study, it is found that the amorphous Mn3Sn can generate a highly efficient spin current with a strong z-direction polarization component due to its spontaneous composition gradient, which switches the perpendicular magnetization in the absence of an external field. The SOT efficiency of gradient-Mn3Sn can be reversibly modulated by the ionic liquid gating based on the migration of hydrogen ions, which reverses the polarity of field-free magnetization switching and allows the realization of 16 binary Boolean logic functions in a single device by pure electrical methods. These results not only offer a very convenient route to field-free magnetization switching but also can promote the development of in-memory computing for spintronic devices.

Dual SOT Switching Modes in a Single Device Geometry for Neuromorphic Computing

Neuromorphic computing aims to replicate the brain's efficient processing through artificial neurons and synapses, requiring binary and multilevel switching. We present a PtMn/(Co/Pd)4/Ta device that uniquely enables dual spin-orbit torque (SOT) switching modes─binary and multilevel (analog)─within the same geometry and stack structure, eliminating the need for device modifications. Binary SOT switching is achieved via domain wall nucleation and propagation at moderate current levels (∼65 mA), while multilevel switching occurs via domain nucleation mode without significant propagation after a high-current treatment (∼85 mA). The transition between two modes originates from structural changes after the current treatment. These modes allow for neuronal and synaptic functionalities, with the device achieving 96% accuracy in digit/letter recognition on the MNIST data set using an artificial neural network (ANN). The device's robust perpendicular magnetic anisotropy (PMA), dual-mode switching under a small in-plane field (HX), and simplified fabrication underscore its promise as an energy-efficient solution for neuromorphic computing.

Large and Tunable Electron-Depletion-Based Voltage-Controlled Magnetic Anisotropy in the CoFeB/MgO System via Work-Function-Engineered PtxW1-x Underlayers

Voltage-Controlled Magnetic Anisotropy (VCMA) effect is a promising strategy for reducing energy consumption in Magnetic Random-Access Memory (MRAM) for embedded applications. However, the low efficiency of VCMA poses challenges for CoFeB/MgO-based MRAM. Although significant VCMA coefficients have been predicted based on electron depletion (ED) in the orbital population model for Fe/MgO interfaces, experimental validation remains limited. Here, we demonstrate an effective and industry-compatible approach to achieving an electrical-field tunable interfacial perpendicular magnetic anisotropy (PMA) and an enhanced VCMA coefficient by synthesizing W-based metallic alloy underlayers with varying Pt concentrations, leveraging Pt's high work function and strong electronegativity. Compared with pure W control devices, the alloy with the highest Pt concentration achieves a VCMA enhancement approximately eight times greater. Additionally, significant electron depletion in the Fe 2p3/2 and 2p1/2 orbitals at the CoFeB/MgO interface is observed through binding energy shifts. High-resolution X-ray photoelectron spectroscopy (HR-XPS) confirms these shifts as increased binding energies, indicating reduced electron density at the interface. These findings suggest that VCMA efficiency in MRAM devices can be enhanced by controlling the Fermi surface at the CoFeB/MgO interface under thermal equilibrium.

Single-Layer Spin-Orbit-Torque Magnetization Switching Due to Spin Berry Curvature Generated by Minute Spontaneous Atomic Displacement in a Weyl Oxide

Spin Berry curvature characterizes the band topology as the spin counterpart of Berry curvature and is crucial in generating novel spintronics functionalities. By breaking the crystalline inversion symmetry, the spin Berry curvature is expected to be significantly enhanced; this enhancement will increase the intrinsic spin Hall effect in ferromagnetic materials and, thus, the spin-orbit torques (SOTs). However, this intriguing approach is not applied to devices; generally, the spin Hall effect in ferromagnet/heavy-metal bilayer is used for SOT magnetization switching. Here, SOT-induced partial magnetization switching is demonstrated in a single layer of a single-crystalline Weyl oxide SrRuO3 (SRO) with a small current density of ≈3.1 × 106 A cm-2. Detailed analysis of the crystal structure in the seemingly perfect periodic lattice of the SRO film reveals barely discernible oxygen octahedral rotations with angles of ≈5° near the interface with a substrate. Tight-binding calculations indicate that a large spin Hall conductivity is induced around small gaps generated at band crossings by the synergy of inherent spin‒orbit coupling and band inversion due to the rotations, causing magnetization reversal. The results indicate that a minute atomic displacement in single-crystal films can induce strong intrinsic SOTs that are useful for spin-orbitronics devices.

Full Electrical Manipulation of Perpendicular Magnetization in [111]-Orientated Pt/Co Heterostructure Enabled by Anisotropic Epitaxial Strain

The effective manipulation of perpendicular magnetization through spin-orbit torque (SOT) holds great promise for magnetic memory and spin-logic device. However, field-free SOT switching of perpendicular magnetization remains a challenge for conventional materials with high symmetry. This study elucidates a full electrical manipulation of the perpendicular magnetization in an epitaxial [111]-orientated Pt/Co heterostructure. A large anisotropic epitaxial strain induces a symmetry transition from the ideal C3v to C1v, attributed to the mismatch between [112] and [110] directions. The anisotropic strain also generates a noteworthy in-plane magnetization component along the [112] direction, further breaking magnetic symmetry. Notably, the high-temperature performance under 393 K highlights the robustness of strain-induced in-plane symmetry breaking. Furthermore, eight Boolean logic operations have been demonstrated within a single SOT device. This research presents a method for harnessing epitaxial strain to break in-plane symmetry, which may open a new avenue in practical SOT devices.

High spin-orbit torque efficiency induced by engineering spin absorption for fully electric-driven magnetization switching

Realizing spin-orbit torque (SOT)-driven magnetization switching offers promising opportunities for the advancement of next-generation spintronics. However, the relatively low charge-spin conversion efficiency accompanied by an ultrahigh critical switching current density (Jc) remains a significant obstacle to the further development of SOT-based storage elements. Herein, spin absorption engineering at the ferromagnet/nonmagnet interface is firstly proposed to achieve high SOT efficiency in Pt/Co/Ir trilayers. The Jc value was significantly decreased to 7.5 × 106 A cm-2, achieving a maximum reduction of 58% when a 4.0-nm Gd layer was inserted into the Co/Ir interface. A similar trend was observed in the trilayers with various rare metal insertions, suggesting the universality of this approach. Simultaneously, the highest effective spin Hall angle of 0.29 was obtained in the Pt/Co/Gd (4.0 nm)/Ir multilayers, which was approximately three times greater than that obtained in the Pt/Co/Ir trilayer. First-principles calculations together with polarized neutron reflectivity results revealed that spin mixed conductivity can be significantly enhanced due to a spontaneous interfacial CoGd alloy, which is critical for high SOT efficiency. In addition, the deterministic field-free switching polarity can be tuned by introducing Gd insertion. These findings provide a promising pathway for deeply understanding the spin-charge conversion mechanism, and further enable the design of low-consumption spintronic circuits.

Strong Damping-Like Torques in Wafer-Scale MoTe2 Grown by MOCVD

The scalable synthesis of materials with strong spin orbit coupling (SOC) is crucial for the development of spintronic and magnetic devices. Here, wafer-scale growth of 1T' MoTe2 using metal-organic chemical vapor deposition (MOCVD) at low temperatures (400 °C) is demonstrated. The synthesized films exhibit uniform coverage across the entire substrate, as well as accurate stoichiometry. This low-temperature synthesis is compatible with silicon back-end-of-line (BEOL) processes, enabling in-memory and in-sensor computing for data-intensive applications. Furthermore, it was found that the grown 1T' MoTe2 exhibits strong spin-orbit coupling, as revealed by the spin torque ferromagnetic resonance (ST-FMR) measurements conducted on a 1T' MoTe2/permalloy bilayer. These measurements indicate significant damping-like torques in the wafer-scale 1T' MoTe2 film and indicate high spin-charge conversion efficiency. The BEOL-compatible process and potent spin orbit torque demonstrate the promise of MOCVD-grown MoTe2 in advanced device applications.

Giant and Anisotropic Enhancement of Spin-Charge Conversion in Graphene-Based Quantum System

The ever-increasing demand for efficient data storage and processing has fueled the search for novel memory devices. By exploiting the spin-to-charge conversion phenomena, spintronics promises faster and low power solutions alternative to conventional electronics. In this work, a remarkable 34-fold increase in spin-to-charge current conversion is demonstrated when incorporating a 2D epitaxial graphene monolayer between iron and platinum layers by exploring spin-pumping on-chip devices. Furthermore, it is found that the spin conversion is also anisotropic. This enhancement and anisotropy is attributed to the asymmetric Rashba contributions driven by an unbalanced spin accumulation at the differently hybridized top and bottom graphene interfaces, as highlighted by ad-hoc first-principles theory. The improvement in spin-to-charge conversion as well as its anisotropy reveals the importance of interfaces in hybrid 2D-thin film systems, opening up new possibilities for engineering spin conversion in 2D materials, leading to potential advances in memory, logic applications, or unconventional computing.

Enhanced Field-Like Torque Generated from the Anisotropic Spin-Split Effect in Triple-Domain RuO2 for Energy-Efficient Spin-Orbit Torque Magnetic Random-Access Memory

Spin-current generation via the anisotropic spin-split effect has been predicted in antiferromagnetic RuO2, where the symmetry of RuO2 plays a critical role in spin-orbit torque (SOT). This phenomenon has garnered attention for its potential to enable energy-efficient spintronic devices, such as SOT magnetic random-access memory. In this study, a high-quality RuO2 (100) epitaxial film with a well-controlled triple-domain-structure is analyzed, and it is confirmed that out-of-plane spin-current generation is independent of the Néel vector (N ⃗ $\vec N$ ). ThisN ⃗ $\vec N$ independence of the out-of-plane spin current leads to equal SOT values for the two orthogonal currents. The spin-split effect-induced SOT demonstrates a field-like (FL) torque efficiency (-0.066 ± 0.001) that is six times higher than that of the Slonczewski-like torque efficiency (-0.011 ± 0.001). Furthermore, micromagnetic simulations show that this high FL torque reduces the critical switching voltage by a factor of 2.6 in the sub-nanosecond regime in an SOT device. These findings contribute to advancing research and the development of highly energy-efficient antiferromagnetic-based SOT magnetic random-access memory.

Observation of Giant Effective Orbital Hall Angle in Ti/Pt Metallic Heterostructure

Orbitronics is an emerging field in which orbital currents are used to develop high-efficiency electronic information devices. Orbital currents have a wider material range and longer transmission distance than spin currents. However, the efficient utilization of orbital currents remains challenging. In this paper, the study reports a giant effective orbital Hall angle in a Ti/Pt metallic heterostructure for efficient magnetization switching. The effective orbital Hall angle of Ti/Pt/Permalloy (Ni81Fe19) reaches 2.4 ± 0.5, a 14-fold increase relative to that of Ti/Ni. By constructing an interface orbital current transmission model, the study found that the effective orbital Hall angle is closely related to the interface spin-orbit coupling. In addition, research obtained a critical magnetization switching current density of Ti/Pt as low as 5.7 × 105 A/cm2, which is comparable to that of topological insulators. Based on this metallic heterostructure, the study demonstrates high-efficiency and low-dissipation Boolean logic operation. These metallic heterostructures, which combine a large effective orbital Hall angle and ease of integration with semiconductors, have significant implications for large-scale orbitronic device applications.

Cryogenic in-memory computing using magnetic topological insulators

Machine learning algorithms have proven to be effective for essential quantum computation tasks such as quantum error correction and quantum control. Efficient hardware implementation of these algorithms at cryogenic temperatures is essential. Here we utilize magnetic topological insulators as memristors (termed magnetic topological memristors) and introduce a cryogenic in-memory computing scheme based on the coexistence of a chiral edge state and a topological surface state. The memristive switching and reading of the giant anomalous Hall effect exhibit high energy efficiency, high stability and low stochasticity. We achieve high accuracy in a proof-of-concept classification task using four magnetic topological memristors. Furthermore, our algorithm-level and circuit-level simulations of large-scale neural networks demonstrate software-level accuracy and lower energy consumption for image recognition and quantum state preparation compared with existing magnetic memristor and complementary metal-oxide-semiconductor technologies. Our results not only showcase a new application of chiral edge states but also may inspire further topological quantum-physics-based novel computing schemes.

Orbital Angular Momentum Correlated Charge to Spin Conversion in Metallic Antiferromagnet

Current-induced spin-orbit torque (SOT) allows efficient electrical manipulation on magnetization in spintronic devices. Maximizing the SOT efficiency is a key goal that is pursued via increasing the net spin generation and accumulation. However, spin transport in antiferromagnets is seriously restricted due to the strong antiferromagnetic coupling, which blocks the development of antiferromagnetic-based devices. Here, a significant enhancement of SOT efficiency in Ir20Mn80 (IrMn)-based heterostructure associated with the orbital effect of naturally oxidized Cu (Cu*) bottom layer is reported. Considering the weak spin-orbit coupling of Cu*, the enhancement results from an orbital current generated from charge current at the Cu*/IrMn interface that contributes to spin current in the IrMn layer due to the strong spin-orbit coupling. The SOT efficiency variation with IrMn thickness reveals the process of orbital angular momentum (OAM) transportation and conversion. Moreover, the contribution of orbital current is verified by the critical current density decreasing of SOT-driven magnetization switching in Cu*/IrMn/[Co/Pt]3 heterostructure. This study opens a path to design high-efficient SOT-based spintronic devices combining the advantages of OAM and metallic antiferromagnets.

Exchange Coupling-Induced Spin Dynamic Damping Modulation at the Py/FeMn Interface

The spin dynamic damping is crucial for applications in magnetic memory, sensors, and logical systems. Here, focusing on interfacial antiferromagnetic exchange coupling, the magneto-dynamics of Ni80Fe20(Py)/Fe50Mn50(FeMn) bilayers is systematically investigated. When the FeMn thickness exceeds 5 nm, an interfacial exchange bias field appears, significantly increasing the spin dynamic damping of the Py/FeMn bilayer to around 0.015. A Cu spacer is introduced between the Py and FeMn layers, and the interfacial exchange bias effect is eliminated following a dramatic decrease in the spin dynamic damping. However, a slight damping increment is observed in Py/Cu/FeMn trilayers, which is attributed to the spin pumping mechanism. Based on spin pumping theory, the estimated interfacial spin mixing conductance is 3.44 nm-2 in Py/Cu/FeMn, which is attributed to the weak spin-orbit coupling of the FeMn layer. These findings indicate that the dynamic damping of Py/FeMn bilayers is primarily driven by interfacial exchange coupling rather than the spin pumping effect. Furthermore, by employing FeMn as an insertion at Py/Pt and Py/Cu interfaces, we demonstrate the short spin diffusion length for the FeMn layer, and we confirm the critical role of interfacial exchange coupling in enhancing spin dynamic damping. The exchange coupling at the Py/FeMn interface facilitates spin relaxation, resulting in the damping enhancement and blocking spin transmission from the Py to Pt (Cu) layer. These findings suggest that integrating antiferromagnetic materials with exchange coupling interfaces could significantly boost high-frequency spintronic applications.

Interfacial Spin-Orbit-Coupling-Induced Strong Spin-to-Charge Conversion at an All-Oxide Ferromagnetic/Quasi-Two-Dimensional Electron Gas Interface

Functional oxides and hybrid structures with interfacial spin-orbit coupling and the Rashba-Edelstein effect (REE) are promising materials systems for thermal tolerance spintronic device applications. Here, we demonstrate efficient spin-to-charge conversion through enhanced interfacial spin-orbit coupling at the all-oxide interface of La1-xCaxMnO3 with quasi-two-dimensional (quasi-2D) SrTiO3 (LCMO/STO). The quasi-2D interface is generated via oxygen vacancies at the STO surface. We obtain a spin-to-charge conversion efficiency of θ∥ ≈ 2.32 ± 1.3 nm, most likely originating from the inverse REE, which is relatively large versus all-metallic spin-to-charge conversion materials systems. The results highlight that the LCMO/STO 2D electron gas is a potential platform for spin-based memory and transistor applications.

Unconventional unidirectional magnetoresistance in heterostructures of a topological semimetal and a ferromagnet

Unidirectional magnetoresistance (UMR) in a bilayer heterostructure, consisting of a spin-source material and a magnetic layer, refers to a change in the longitudinal resistance on the reversal of magnetization and originates from the interaction of non-equilibrium spin accumulation and magnetization at the interface. Since the spin polarization of an electric-field-induced non-equilibrium spin accumulation in conventional spin-source materials is restricted to be in the film plane, the ensuing UMR can only respond to the in-plane component of magnetization. However, magnets with perpendicular magnetic anisotropy are highly desired for magnetic memory and spin-logic devices, whereas the electrical read-out of perpendicular magnetic anisotropy magnets through UMR is critically missing. Here we report the discovery of an unconventional UMR in the heterostructures of a topological semimetal (WTe2) and a perpendicular magnetic anisotropy ferromagnetic insulator (Cr2Ge2Te6), which allows to electrically read the up and down magnetic states of the Cr2Ge2Te6 layer through longitudinal resistance measurements.

Electrically switchable ON-OFF spin-orbit torque in an ionic-gated metallic trilayer

With the advancement of magnetization-based spintronic applications, there has been considerable interest in spin-orbit torque as an electric technique to dynamically manipulate magnetization. In this study, gate-induced ON-OFF switchable spin-orbit torque in Pt/Co/Pt spin-orbit device using the ionic gating technique is reported. By canceling the spin currents from Pt layers, the OFF state is attained in Pt/Co/Pt spin-orbit device. Notably, under a strong negative gate electric field applied to the Pt/Co/Pt spin-orbit device, the damping-like spin-orbit torque is markedly enhanced over sixfold compared with the applied positive gate electric field. We show that the gate modulation of the spin-orbit torque in the Pt/Co/Pt spin-orbit device can be explained by considering the change of the spin-charge interconversion by electric gating. This research serves as a promising avenue for electrically programmable spintronic devices.

Anomalous Hall spin current drives self-generated spin-orbit torque in a ferromagnet

Spin-orbit torques enable energy-efficient manipulation of magnetization by electric current and hold promise for applications ranging from non-volatile memory to neuromorphic computing. Here we report the discovery of a giant spin-orbit torque induced by anomalous Hall current in ferromagnetic conductors. This anomalous Hall torque is self-generated as it acts on the magnetization of the ferromagnet that engenders the torque. The magnitude of the anomalous Hall torque is sufficiently large to fully negate magnetic damping of the ferromagnet, which allows us to implement a microwave spin torque nano-oscillator driven by this torque. The peculiar angular symmetry of the anomalous Hall torque favours its use over the conventional spin Hall torque in coupled nano-oscillator arrays. The universal character of the anomalous Hall torque makes it an integral part of the description of coupled spin transport and magnetization dynamics in magnetic nanostructures.

Fully Field-Free Spin-Orbit Torque Switching Induced by Spin Splitting Effect in Altermagnetic RuO2

Altermagnetism, a newly identified class of magnetism blending characteristics of both ferromagnetism and antiferromagnetism, is emerging as a compelling frontier in spintronics. This study reports a groundbreaking discovery of robust, 100% field-free spin-orbit torque (SOT) switching in a RuO2(101)/[Co/Pt]2/Ta structure. The experimental results reveal that the spin currents, induced by the in-plane charge current, flow along the [100] axis, with the spin polarization direction aligned parallel to the Néel vector. These z-polarized spins generate an out-of-plane anti-damping torque, enabling deterministic switching of the Co/Pt layer without the necessity of an external magnetic field. The altermagnetic spin splitting effect (ASSE) in RuO2 promotes the generation of spin currents with pronounced anisotropic behavior, maximized when the charge current flows along the [010] direction. This unique capability yields the highest field-free switching ratio, maintaining stable SOT switching even under a wide range of external magnetic fields, demonstrating exceptional resistance to magnetic interference. Notably, the ASSE-dominated spin current is found to be most effective when the current is aligned with the [010] direction. The study highlights the potential of RuO2 as a powerful spin current generator, opening new avenues for advancing spin-torque switching technologies and other cutting-edge spintronic devices.

Current-Driven Magnetization Switching for Superconducting Diode Memory

Stacking superconductors (SC) with ferromagnetic materials (FM) significantly impact superconductivity, enabling the emergence of spin-triplet states and topological superconductivity. The tuning of superconductivity in SC-FM heterostructure is also reflected in the recently discovered superconducting diode effect, characterized by nonreciprocal electric transport when time and inversion symmetries are broken. Notably, in SC-FM systems, a time reversal operation reverses both current and magnetization, leading to the conceptualization of superconducting magnetization diode effect (SMDE). In this variant, while the current direction remains fixed, the critical currents shall be different when reversing the magnetization. Here, the existence of SMDE in SC-FM heterostructures is demonstrated. SMDE uniquely maps magnetization states onto superconductivity by setting the read current between two critical currents for the positive and negative magnetization directions, respectively. Thus, the magnetization states can be read by measuring the superconductivity, while the writing process is accomplished by manipulating magnetization states through current-driven spin-orbit torque to switch the superconductivity. The proposed superconducting diode magnetoresistance in SC-FM heterostructures with an ideally infinite on/off ratio resolves the limitations of tunneling magnetoresistance in the magnetic tunneling junctions, thereby contributing to the advancement of superconducting spintronics.

Giant Modulation of Magnetoresistance in a Van Der Waals Magnet by In-Plane Current Injection

Efficient magnetization control is a central issue in magnetism and spintronics. Particularly, there are increasing demands for manipulation of magnetic states in van der Waals (vdW) magnets with unconventional functionalities. However, the electrically induced phase transition between ferromagnetic-to-antiferromagnetic states without external magnetic field is yet to be demonstrated. Here, the current-induced magnetic phase transition in a vdW ferromagnet Fe5GeTe2 is reported. Based on magneto-transport measurements and theoretical analysis, it is demonstrated that transition in the interlayer magnetic coupling occurs through vertical voltage drop between layers induced by current which is attributed to high anisotropy of the resistivity caused by the vdW gaps. Such magnetic phase transition results in giant modulation of the longitudinal magnetoresistance from 5% to 170%. The electrical tunability of the magnetic phase in Fe5GeTe2 with current-in-plane geometry opens a path for electric control of magnetic properties, expanding the ability to use vdW magnets for spintronic applications.

Closed Loop Superparamagnetic Tunnel Junctions for Reliable True Randomness and Generative Artificial Intelligence

Physical devices exhibiting stochastic functions with low energy consumption and high device density have the potential to enable complex probability-based computing algorithms, accelerate machine learning, and enhance hardware security. Recently, superparamagnetic tunnel junctions (sMTJs) have been widely explored for such purposes, leading to the development of sMTJ-based systems; however, the reliance on nanoscale ferromagnets limits scalability and reliability, making sMTJs sensitive to external perturbations and prone to significant device variations. Here, we present an experimental demonstration of closed loop three-terminal sMTJs as reliable and potentially scalable sources of true randomness, in the absence of external magnets. By leveraging dual-current controllability and incorporating feedback, we stabilize the switching operation of superparamagnets and reach cryptographic-quality random bitstreams. The realization of controllable and robust true random sMTJs underpins a general hardware platform for computing schemes exploiting the stochasticity in the physical world, as demonstrated by the generative artificial intelligence example in our experiment.

Nonreciprocity in Magnon Mediated Charge-Spin-Orbital Current Interconversion

In magnetic systems, angular momentum is carried by spin and orbital degrees of freedom. Nonlocal devices, comprising heavy-metal nanowires on magnetic insulators like yttrium iron garnet (YIG), enable angular momentum transport via magnons. These magnons are polarized by spin accumulation at the interface through the spin Hall effect (SHE) and detected via the inverse SHE (iSHE). The processes are generally reciprocal, as demonstrated by comparable efficiencies when reversing injector and detector roles. However, introducing Ru, which enables the orbital Hall effect (OHE), disrupts this reciprocity. In our system, magnons polarized through combined SHE and OHE and detected via iSHE are 35% more efficient than the reverse process. We attribute this nonreciprocity to nonzero spin vorticity, resulting from varying electron drift velocities across the Pt/Ru interface. This study highlights the potential of orbital transport mechanisms in influencing angular momentum transport and efficiency in nonlocal spintronic devices.

Large Spin-Orbit Torque in a-Plane α-Fe_{2}O_{3}/Pt Bilayers

Realization of efficient spin-orbit torque switching of the Néel vector in insulating antiferromagnets is a challenge, often complicated by spurious effects. Quantifying the spin-orbit torques in antiferromagnet or heavy metal heterostructures is an important first step toward this goal. Here, we employ magneto-optic techniques to study dampinglike spin-orbit torque (DL-SOT) in a-plane α-Fe_{2}O_{3} (hematite) with a Pt spin-orbit overlayer. We find that the DL-SOT efficiency is 2 orders of magnitude larger than reported in c- and r-plane hematite/Pt using harmonic Hall techniques. The large magnitude of DL-SOT is supported by direct imaging of current-induced motion of antiferromagnetic domains that happens at moderate current densities. Our study introduces a new method for quantifying spin-orbit torque in antiferromagnets with a small canted moment and identifies a-plane α-Fe_{2}O_{3} as a promising candidate to realize efficient SOT switching.

Intrinsic Solution to the Dilemma between High-Efficiency and External-Field-Free Spin-Orbit Torque Switching Based on Biaxial Devices

Spin-orbit torque (SOT) is widely considered to be a fast and robust writing scheme for magnetic random-access memories (MRAMs). However, the requirements of field-free switching and high switching efficiency are often incompatible in SOT devices, placing a critical challenge on its improvement. Here we propose that by utilizing biaxial systems the dilemma between high-efficiency and external-field-free SOT switching can be solved intrinsically. We further demonstrate the feasibility of the proposed writing scheme in a MgO/Fe/W device and show that the intrinsic multistate storage ability of the biaxial device compensates its additional area requirement. These results are expected to pave the way toward the further development of SOT-MRAMs.

Electrical mutual switching in a noncollinear-antiferromagnetic-ferromagnetic heterostructure

Spin-orbit torque (SOT) provides a promising mechanism for electrically encoding information in magnetic states. Unlike existing schemes, where the SOT is passively determined by the material and device structures, an active manipulation of the intrinsic SOT polarity would allow for flexibly programmable SOT devices. Achieving this requires electrical control of the current-induced spin polarization of the spin source. Here we demonstrate a proof-of-concept current-programmed SOT device. Using a noncollinear-antiferromagnetic/nonmagnetic/ferromagnetic Mn3Sn/Mo/CoFeB heterostructure at zero magnetic field, we show current-induced switching in the CoFeB layer due to the spin current polarized by the magnetic structure of the Mn3Sn; by properly tuning the driving current, the spin current from the CoFeB further reverses the magnetic orientation of the Mn3Sn, which determines the polarity of the subsequent switching of the CoFeB. This scheme of mutual switching can be achieved in a spin-valve-like simple protocol because each magnetic layer serves as a reversible spin source and target magnetic electrode. It yields intriguing proof-of-concept functionalities for unconventional logic and neuromorphic computing.

Manipulation of Unconventional Spin Polarization in Non-Collinear Exchange-Spring Magnetic Structures

Manipulating the polarization of spin current is essential for understanding the mechanism of charge-to-spin conversion and achieving efficient electrically driven magnetization switching. Here, a novel exchange-spring magnetic structure is introduced formed by the coupling of perpendicular magnetic anisotropy (PMA) CoTb and in-plane magnetic anisotropy (IMA) Co films. When a spin current with the polarization along the y-direction flows through this exchange-spring (x-z plane) structure, the interaction between the y-spin and the local exchange field with a non-collinear spatial distribution gives rise to substantial unconventional spin polarizations in the x- and z-directions, enabling field-free spin-orbit torque driven perpendicular magnetization switching at room temperature. More importantly, the polarization directions of this unconventional spin current can be reversed depending on whether the interfacial exchange coupling is ferromagnetic or antiferromagnetic. This work establishes a platform to explore emergent mechanisms for manipulating unconventional spin polarization with rich non-collinear magnetic exchange spin structures.

Enhancing Field-Like Efficiency Via Interface Engineering with Sub-Atomic Layer Ta Insertion

The prevailing research emphasis has been on reducing the critical switching current density (Jc) by enhancing the damping-like efficiency (βDL). However, recent studies have shown that the field-like efficiency (βFL) can also play a major role in reducing Jc. In this study, the central inversion asymmetry of Pt-Co is significantly enhanced through interface engineering at the sub-atomic layer of Ta, thereby inducing substantial alterations in the βFL associated with the interface. The βFL has shown a 123% increase, from -1.66 Oe/(MA cm- 2) to -3.8 Oe/(MA cm- 2). As a result, the multilayered Ta/Pt/Ta (0.3 nm insertion)/Co/Ta structure leads to a notable decrease in Jc, exceeding a remarkable 90% compared to the simpler Ta/Pt/Co/Ta structure, ultimately achieving a significantly low value of 2.7 MA cm- 2. These findings pave the way for the development of highly efficient and energy-saving spin-orbit torque (SOT)-based spintronic devices, where further optimizations in interface engineering can unlock even greater potential in terms of reduced power consumption and enhanced performance.

Electrical Spin State Manipulation in All-Magnet Heterojunctions Using a Ferromagnetic Spin Source

The ability to electrically manipulate spin states in magnetic materials is essential for the advancement of energy-efficient spintronic device, which is typically achieved in systems composed of a spin source and a magnetic target, where the magnetic state of the target is altered by a charge current. While theories suggest that ferromagnets could function as more versatile spin sources, direct experimental studies involving only the spin source and target layers have been lacking. Here electrical manipulation of spin states in noncolinear antiferromagnet Mn3Sn using ferromagnets (Ni, Fe, NiFe, CoFeB) as the spin sources is reported. Both field-free switching and switching with an assistive field are achieved in Mn3Sn/ferromagnet bilayers, where the switching polarity correlates with the sign of anomalous Hall effect of the ferromagnets. The experimental findings can be accounted for by the presence of spin currents arising from spin-dependent scattering within the ferromagnets. This finding provides valuable insights into the underlying mechanisms of spin-conversion in ferromagnets, offering an alternative spin source for novel technological applications.

Artificial Control of Giant Converse Magnetoelectric Effect in Spintronic Multiferroic Heterostructure

To develop voltage-controlled magnetization switching technologies for spintronics applications, a highly (422)-oriented Co2FeSi layer on top of the piezoelectric PMN-PT(011) is experimentally demonstrated by inserting a vanadium (V) ultra-thin layer. The strength of the growth-induced magnetic anisotropy of the (422)-oriented Co2FeSi layers can be artificially controlled by tuning the thicknesses of the inserted V and the grown Co2FeSi layers. As a result, a giant converse magnetoelectric effect (over 10-5 s m-1) and a non-volatile binary state at zero electric field are simultaneously achieved in the (422)-oriented Co2FeSi/V/PMN-PT(011) multiferroic heterostructure. This study leads to a way toward magnetoresistive random-access-memory (MRAM) with a low power writing technology.

Controllable z-Polarized Spin Current in Artificially Structured Ferromagnetic Oxide with Strong Spin-Orbit Coupling

Realizing field-free switching of perpendicular magnetization by spin-orbit torques is crucial for developing advanced magnetic memory and logic devices. However, existing methods often involve complex designs or hybrid approaches, which complicate fabrication and affect device stability and scalability. Here, we propose a novel approach using z-polarized spin currents for deterministic switching of perpendicular magnetization through interfacial engineering. We fabricate La0.67Sr0.33MnO3-SrIrO3 (LSIMO) thin films with robust spin-orbit coupling and ferromagnetic order through orbital and lattice reconstruction, integrating SrIrO3 and La0.67Sr0.33MnO3 materials. Our investigation reveals that y- and z-polarized spin currents, driven by the spin Hall and spin-orbit precession effects, enable field-free switching of perpendicular magnetization. Notably, the z-polarized spin currents are tunable via the in-plane magnetization of LSIMO. These findings present a promising pathway for the development of energy-efficient spintronic devices, offering improved performance and scalability.

Two-Dimensional Materials for Brain-Inspired Computing Hardware

Recent breakthroughs in brain-inspired computing promise to address a wide range of problems from security to healthcare. However, the current strategy of implementing artificial intelligence algorithms using conventional silicon hardware is leading to unsustainable energy consumption. Neuromorphic hardware based on electronic devices mimicking biological systems is emerging as a low-energy alternative, although further progress requires materials that can mimic biological function while maintaining scalability and speed. As a result of their diverse unique properties, atomically thin two-dimensional (2D) materials are promising building blocks for next-generation electronics including nonvolatile memory, in-memory and neuromorphic computing, and flexible edge-computing systems. Furthermore, 2D materials achieve biorealistic synaptic and neuronal responses that extend beyond conventional logic and memory systems. Here, we provide a comprehensive review of the growth, fabrication, and integration of 2D materials and van der Waals heterojunctions for neuromorphic electronic and optoelectronic devices, circuits, and systems. For each case, the relationship between physical properties and device responses is emphasized followed by a critical comparison of technologies for different applications. We conclude with a forward-looking perspective on the key remaining challenges and opportunities for neuromorphic applications that leverage the fundamental properties of 2D materials and heterojunctions.

Altermagnetism: A Chemical Perspective

Altermagnets have been recently introduced as a classification of collinear, spin compensated magnetic materials that host net-zero magnetization yet display some electronic behaviors typically associated with noncompensated magnetic materials like ferromagnets. The emergence of such properties are a consequence of spin-split bands that arise under specific symmetry conditions in the limit of zero spin-orbit coupling. In this Perspective, we summarize the fundamental criteria for realizing an altermagnetic phase and present a qualitative electronic band structure derivation and symmetry analysis through chemical principles. We then discuss the properties that make altermagnets distinctive candidates for charge-to-spin conversion elements in spintronic devices and provide a brief review of some altermagnetic candidate materials. Finally, we discuss future directions for altermagnetism and highlight opportunities for chemists to advance this emerging field.

Enhancing Rashba Spin-Splitting Strength by Orbital Hybridization

A Rashba spin-splitting state with spin-momentum locking enables the charge-spin interconversion known as the Rashba effect, induced by the interplay of inversion symmetry breaking (ISB) and spin-orbit coupling (SOC). Enhancing spin-splitting strength is promising to achieve high spin-orbit torque (SOT) efficiency for low-power-consumption spintronic devices. However, the energy scale of natural ISB at the interface is relatively small, leading to the weak Rashba effect. In this work, we report that orbital hybridization inducing additional asymmetry potential at the interface observably enhances spin-splitting strength, verified in the hexagonal boron nitride (h-BN)/Co3Pt heterostructures. First-principles calculations suggest the sizable Rashba spin-splitting derived from the out-of-plane p-d hybridization combined with SOC at the h-BN/Co3Pt interface. Then, the SOT efficiency is observably enhanced via the Rashba effect at the h-BN/Co3Pt interface and exhibits unusual temperature dependence, in which the large-area h-BN is in situ grown on the Co3Pt layer with perpendicular magnetic anisotropy by magnetron sputtering. Especially, the dominant damping-like torque is observed, resulting in the lower threshold switching current density and the enhanced switching ratio. Our results provide opportunities for interfacial control to enhance the Rashba effect and the SOT efficiency in heterostructures. It is expected to contribute to the design of energy-efficient spintronic devices.

Room-Temperature Ferromagnetism with Strong Spin-Orbit Coupling Achieved in CaRuO3 Interfacial Phase via Magnetic Proximity Effect

Recently, theoretical and experimental research predicted that ferromagnets with strong spin-orbit coupling (SOC) could serve as spin sources with dramatically enhanced spin-orbit torque (SOT) efficiency due to the combination of spin Hall effect and anomalous Hall effect (AHE), presenting potential advantages over conventional nonmagnetic heavy metals. However, materials with a strong SOC and room-temperature ferromagnetism are rare. Here, we report on a ferromagnetic (FM) interfacial phase with Curie temperature exceeding 300 K in the heavy transition-metal oxide CaRuO3, in proximity to La0.67Sr0.33MnO3. Electron energy loss and polarized neutron reflectometry spectra reveal the strong charge transfer from Ru to Mn at the interface, triggering antiferromagnetic exchange interactions between interfacial Ru/Mn ions and thus transferring magnetic order from La0.67Sr0.33MnO3 to CaRuO3. An obvious advantage of such interfacial phase is the enhanced anomalous Hall effect at temperatures from 150 to 300 K. Compared to the most promising room-temperature ferromagnetic oxide La0.67Sr0.33MnO3, the anomalous Hall conductivity σxyAHE (or anomalous Hall angle θH) of CaRuO3/La0.67Sr0.33MnO3 superlattices is increased by 30 (or 31) times at 150 K and 10 (or 3) times at 300 K. This work demonstrates a special approach for inducing ferromagnetism in heavy transition-metal oxides with strong SOC, offering promising prospects for all-oxide-based spintronic applications.

Gyro-spintronic material science using vorticity gradient in solids

We present a novel method for generating spin currents using the gyromagnetic effect, a phenomenon discovered over a century ago. This effect, crucial for understanding the origins of magnetism, enables the coupling between various macroscopic rotational motions and electron spins. While higher rotational speeds intensify the effect, conventional mechanical rotations, typically, below 10,000 RPM, produce negligible results comparable to geomagnetic fluctuations, limiting applied research. Our studies demonstrate that spin current generation comparable to that of rare metals can be achieved through atomic rotations induced by GHz-range surface acoustic waves and the rotational motion of conduction electrons in metallic thin films with nanoscale gradient modulation of electrical conductivity. These effects, termed the acoustic gyromagnetic effect and the current-vorticity gyromagnetic effect, are significant in different contexts. The acoustic gyromagnetic effect is notable in high-conductivity materials like aluminum and copper, which are more abundant than conventional spintronics materials with strong spin-orbit interactions (SOIs). Conversely, the current-vorticity gyromagnetic effect requires a large conductivity gradient to produce current vorticity efficiently. This is achieved by using composition gradient structures from highly conductive metals to poorly conductive oxides or semiconductors. Consequently, unlike traditional strong-SOI materials, we can create highly efficient spin current generators with low energy dissipation due to reduced Joule loss.

Memcapacitors and Memristor Characteristics of ISGE-SOT and SHE-SOT Gain-Driven MoS2:Er Ferromagnets

The enhancement of the spin-orbit torque (SOT) effect through the integration of intrinsic inverse spin galvanic effect spin-orbit torque and spin Hall effect spin-orbit torque is fundamentally dependent on the structural and material properties of the ferromagnets. Consequently, the synthesis of ferromagnets with superior structural integrity and material characteristics is of paramount importance. In this study, a gas-liquid chemical reaction, in conjunction with ultrasonic crushing, was employed to synthesize few-layer MoS2:Er nanosheets. X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive spectroscopy analyses confirm the successful substitution of Mo4+ by Er3+ through doping within the MoS2 lattice. Vibrating sample magnetometry and MT measurements indicate that MoS2:Er exhibits room-temperature ferromagnetism (RTFM), with the underlying mechanism elucidated through first-principles calculations. Furthermore, the unique electron density of states at the Fermi level suggests the presence of ferromagnetism in MoS2:Er. A wedge-shaped Pt/MoS2:Er/Au structure was fabricated and subsequently evaluated for current-induced SOT switching, as well as for its memcapacitor and memristor characteristics. The precession of a magnetic moment in three-dimensional space was successfully simulated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation using the Mumax.

Comparative Study of Current-Induced Torque in Cr/CoFeB/MgO and W/CoFeB/MgO

Orbital torque (OT) in magnetic heterostructures has been actively discussed in terms of its actual existence and usefulness in comparison to the spin-orbit torque (SOT) that shows promise for next-generation magnetoresistive random access memories. The objectives of this study are 2-fold: (i) making an apples-to-apples comparison in two representative stacks where OT and SOT are expected to dominate and (ii) examining the potential emergence of OT in archetypal SOT stacks. Cr/CoFeB/MgO and W/CoFeB/MgO are chosen as the OT- and SOT-dominant systems, respectively. Systematic variations in each layer's thicknesses reveal that (i) Cr/CoFeB/MgO exhibits substantial torque comparable to or even exceeding that of the W/CoFeB/MgO stack when Cr and CoFeB layers are especially thick and (ii) the torque in W/CoFeB/MgO changes sign with increasing W and CoFeB thicknesses, suggesting a crossover of the dominant mechanism from SOT to OT. The findings clarify the opportunities and challenges of devices leveraging SOT and OT.

Diode and Selective Routing Functionalities Controlled by Geometry in Current-Induced Spin-Orbit Torque Driven Magnetic Domain Wall Devices

Research on current-induced domain wall (DW) motion in heavy metal/ferromagnet structures is crucial for advancing memory, logic, and computing devices. Here, we demonstrate that adjusting the angle between the DW conduit and the current direction provides an additional degree of control over the current-induced DW motion. A DW conduit with a 45° section relative to the current direction enables asymmetrical DW behavior: for one DW polarity, motion proceeds freely, while for the opposite polarity, motion is impeded or even blocked in the 45° zone, depending on the interfacial Dzyaloshinskii-Moriya interaction strength. This enables the device to function as a DW diode. Leveraging this velocity asymmetry, we designed a Y-shaped DW conduit with one input and two output branches at +45° and -45°, functioning as a DW selector. A DW injected into the junction exits through one branch, while a reverse polarity DW exits through the other, demonstrating selective DW routing.

Lead-Free Hybrid Perovskite: An Efficient Room-Temperature Spin Generator via Large Interfacial Rashba Effect

Two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) shows great potential for developing flexible and wearable spintronic devices by serving as spin sources via the bulk Rashba effect (BRE). However, the practical application of BRE in 2D HOIP faces huge challenges, particularly due to the toxicity of lead, which is crucial for achieving large spin-orbit coupling, and the restrictions in 2D HOIP candidates to meet specific symmetry-breaking requirements. To overcome these obstacles, we designed a strategy to exploit the interfacial Rashba effect (IRE) of lead-free 2D HOIP (C6H5CH2CH2NH3)2CuCl4 (PEA-CuCl), manifesting as an efficient spin generator at room temperature. IRE of PEA-CuCl originates from the large orbital hybridization at the interface between PEA-CuCl and adjacent ferromagnetic layers. Spin-torque ferromagnetic resonance measurements further quantify a large Rashba effective field of 14.04 Oe per 1011 A m-2, surpassing those of lead-based HOIP and traditional all-inorganic heterojunctions with noble metals. Our lead-free 2D HOIP PEA-CuCl, which harnesses large IRE for spin generation, is efficient, nontoxic, and economic, offering huge promise for future flexible and wearable spintronic devices.

Colossal Orbital Current Induced by Gradient Oxidation for High-Efficiency Magnetization Switching

Orbital angular momentum flow can be used to develop a low-dissipation electronic information device by manipulating the orbital current. However, efficiently generating and fully harnessing orbital currents is a formidable challenge. In this study, an approach is presented that induces a colossal orbital current by gradient oxidation in Pt/Ta to enhance spin-orbit torque (SOT) and achieve high-efficiency magnetization switching. The maximum efficiency of the SOT before and after the gradient oxidation of Ta is improved relative to that of Pt by ≈600 and 1200%, respectively. The large SOT originates from the colossal orbital current because of the orbital Rashba-Edelstein effect induced by the gradient oxidation of Ta. In addition, a large spin-to-charge conversion efficiency is observed in yttrium iron garnet/Pt/TaOx because of the inverse orbital Rashba-Edelstein effect. Harnessing the orbital current can help effectively minimize the critical current density of the current-induced magnetization switching to 2.26-1.08 × 106 A cm-2, marking a 12-fold reduction compared to that using Pt. This findings provide a new path for research on low-dissipation spin-orbit devices and improve the tunability of orbital current generation.

Collinear Spin Current Induced by Artificial Modulation of Interfacial Symmetry

Current induced spin-orbit torque (SOT) manipulation of magnetization is pivotal in spintronic devices. However, its application for perpendicular magnetic anisotropy magnets, crucial for high-density storage and memory devices, remains nondeterministic and inefficient. Here, a highly efficient approach is demonstrated to generate collinear spin currents by artificial modulation of interfacial symmetry, achieving 100% current-induced field-free SOT switching in CoFeB multilayers with perpendicular magnetization on stepped Al2O3 substrates. This field-free switching is primarily driven by the out-of-plane anti-damping SOT generated by the planar spin Hall effect (PSHE), resulting from reduced interface symmetry due to orientation-determined steps. Microscopic theoretical analysis confirms the presence and significance of PSHE in this process. Notably, this method for generating out-of-plane spin polarization along the collinear direction of the spin-current with artificial modulation of interfacial symmetry, overcomes inherent material symmetry constraints. These findings provide a promising avenue for universal control of spin-orbit torque, addressing challenges associated with low crystal symmetry and highlighting its great potential to advance the development of energy-efficient spintronic devices technology.

Large unidirectional spin Hall magnetoresistance in FeNi/Pt/Bi2Se3 trilayers by Pt interfacial engineering

Unidirectional spin Hall magnetoresistance (USMR) has emerged as a promising candidate for magnetoresistive random-access memory (MRAM) technology. However, the realization of high signal-to-noise output signal in USMR devices has remained a challenge, primarily due to the limited USMR effect at room temperature. In this study, we report a large USMR effect in FeNi/Pt/Bi₂Se₃ trilayers through interfacial engineering with Pt to optimize the spin current transmission efficiency and electron-magnon scattering. Our devices exhibit a USMR value that is an order of magnitude higher than previously reported systems, reaching 30.6 ppm/MA/cm² at room temperature. First-principles calculations and experimental observations suggest that the Pt layer not only preserves the spin-momentum locked topological surface states in Bi₂Se₃ at the Fermi-level but also generates additional Rashba surface states within the Pt itself to enhance the effective SOT efficiency. Furthermore, we demonstrate that the two-terminal USMR-MRAM devices show robust output performance with 2nd harmonic resistance variation around 0.11 Ω/mA. Remarkably, the performance of these devices further improves at elevated temperatures, highlighting their potential for reliable operation in a wide range of environmental conditions. Our findings pave the way for future advancements in high-performance, energy-efficient spintronic memory devices.