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2D layered materials with broken inversion symmetry are being extensively pursued as  spin source layers to realize high-efficiency magnetic switching. Such low-symmetry layered systems are, however, scarce. In addition, most layered magnets with perpendicular magnetic anisotropy show a low Curie temperature. Here, the experimental observation of spin-orbit torque magnetization self-switching at room temperature in a layered polar ferromagnetic metal, Fe2.5 Co2.5 GeTe2 is reported. The spin-orbit torque is generated from the broken inversion symmetry along the c-axis of the crystal. These results provide a direct pathway toward applicable 2D spintronic devices.

In this paper, we review our work on the manipulation of magnetization in ferromagnetic semiconductors (FMSs) using electric-current-induced spin-orbit torque (SOT). Our review focuses on FMS layers from the (Ga,Mn)As zinc-blende family grown by molecular beam epitaxy. We describe the processes used to obtain spin polarization of the current that is required to achieve SOT, and we briefly discuss methods of specimen preparation and of measuring the state of magnetization. Using specific examples, we then discuss experiments for switching the magnetization in FMS layers with either out-of-plane or in-plane easy axes. We compare the efficiency of SOT manipulation in single-layer FMS structures to that observed in heavy-metal/ferromagnet bilayers that are commonly used in magnetization switching by SOT. We then provide examples of prototype devices made possible by manipulation of magnetization by SOT in FMSs, such as read-write devices. Finally, based on our experimental results, we discuss future directions which need to be explored to achieve practical magnetic memories and related applications based on SOT switching. [ABSTRACT FROM AUTHOR]

The ability to achieve perpendicular magnetization switching via spin–orbit torques (SOTs) is a critical advance for the development of the next generation of spintronic applications. However, the use of an external magnetic field to break the mirror symmetry is typically required to facilitate current-induced magnetization switching, which poses a significant challenge for practical implementation. Here, we demonstrate the field-free magnetization switching in the Y3Fe5O12 (YIG)/Pt heterostructure. This is achieved by introducing a lateral structure asymmetry in our devices, which can lead to an out-of-plane effective field. Our results provide an alternative solution for achieving field-free magnetization switching in nanoscale ferrimagnet-based heterostructures, thereby advancing the development of emerging SOT-based devices. [ABSTRACT FROM AUTHOR]

Spintronic devices with heavy metal/ferromagnet structures have shown potential applications for in‐memory computing. However, the sensitivity of ferromagnet to external magnetic field raises a challenge for the practical applications of these devices. The usage of synthetic antiferromagnet (SAF) can effectively address this issue due to its good magnetic field immunity. This work demonstrates the implementation of all 16 types of Boolean logic functions via controlling the magnetization states of the SAF layer by using current pulses, and also the stable multistate storage under the interference of perpendicular magnetic field in these devices. The SAF devices also exhibit synaptic plasticity under the stimulation of current pulses. The artificial neural network constructed based on the SAF device can perform handwritten digit recognition tasks with an accuracy rate of 90%. These results showcase the viability and superiority of the SAF device in building logic‐in‐memory architecture for its strong immunity to magnetic field interference. [ABSTRACT FROM AUTHOR]

AbstractThis work deals with the static and dynamic characteristics of the transverse Bloch domain wall within a bilayer nanostructure comprising a ferromagnetic layer and a non-magnetic heavy metal layer. We examine the spatiotemporal evolution of magnetization within the ferromagnetic layer using the one-dimensional Extended Landau-Lifshitz-Gilbert equation under the combined impact of axial and transverse magnetic fields, spin-polarized electric currents, interfacial Dzyaloshinskii-Moriya interaction, nonlinear dry-friction damping, Rashba, and Spin-Hall effect. To characterize the domain wall motion, we first compute the magnetization profile in the two distant domains and analyze the static profile solely influenced by the external transverse magnetic field. We present a new Walker’s type trial function and, applying a small angle approximation approach, establish an analytical expression of the dynamical quantities: domain wall velocity, displacement, moving domain wall profile, and excitation angles. Finally, the results are illustrated via numerical investigation. [ABSTRACT FROM AUTHOR]

Topological insulator (TI) BiSb is a promising material for spin–orbit torque (SOT) devices because it has a high spin Hall angle, relatively higher electrical conductivity, and can be produced at RT by physical vapor deposition. In this work, we systematically investigate the effects of doping BiSb with several dopants. We found that doping with elemental dopants does not change the bulk conductivity, but doping with metal nitride or metal oxide molecular dopants can substantially increase or decrease BiSb's bulk film conductivity with minor impacts on its TI properties. Furthermore, doping can significantly improve other TI film material properties, such as increased melting point and film hardness, producing smaller grain sizes with improved interfacial roughness, and enhanced (012) film growth texture, all of which can contribute to enhanced atomic migration resistance in and out of the BiSb layer. Thus, our results open a path for using doped BiSb in integrated SOT devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Magnetic memory based on spin‐orbit torque (SOT) is a promising candidate for the next‐generation storage devices. Materials that generate out‐of‐plane spin polarization (σz) are highly desired and actively pursued as the SOT generator, due to its ability to achieve field‐free SOT switching of perpendicular magnetization. However, integrating σz into perpendicular magnetic tunnel junction for efficient data writing is not realized. Here, utilizing σz from antiferromagnetic spin Hall effect in Mn2Au, σz‐enabled field‐free SOT switching of perpendicular magnetic tunnel junctions is realized demonstrating a magnetic memory with both writing and reading electrically. The tunnel magnetoresistance ratio achieves 66% with a critical current density of 5.6 × 106 A cm−2 at room temperature. Such field‐free fully SOT switching is further directly confirmed by domain imaging via magneto‐optical Kerr effect microscopy. In addition to enabling field‐free switching, σz is proposed to assist ultrafast and more efficient switching of perpendicular magnetization compared with conventional in‐planes ones, based on simulations. This research advances the application of out‐of‐plane SOTs and paves the way for high‐density, high‐speed, and low‐power magnetic memory. [ABSTRACT FROM AUTHOR]

In this study, deterministic current‐induced spin‐orbit torque (SOT) magnetization switching is achieved, particularly in systems with perpendicular magnetic anisotropy (PMA), without the need for a collinear in‐plane field, a traditionally challenging requirement. In a Ta/CoFeB/MgO/NiO/Ta structure, spin reflection at the MgO/NiO interface generates a spin current with an out‐of‐plane spin polarization component σz. Notably, the sample featuring 0.8 nm MgO and 2 nm NiO demonstrates an impressive optimal switching ratio approaching 100% without any in‐plane field. A systematic investigation of the effects of the MgO and NiO thickness demonstrates that the formation of noncollinear spin structures and canted magnetization in the ultrathin NiO interlayer plays a pivotal role to the field‐free SOT switching. The integration of NiO as an antiferromagnetic insulator effectively mitigates current shunting effects and enhances the thermal stability of the device. This advancement in the CoFeB/MgO system holds promise for significant applications in spintronics, marking a crucial step toward realizing innovative technologies. [ABSTRACT FROM AUTHOR]

Synthetic antiferromagnet (SAF) with high thermal stability, ultra‐fast spin dynamics, and highly efficient spin‐orbit torque switching has great application potential in neuromorphic computing hardware. However, two challenges, the weakening of Hall signal in the remanent state and the need for a large auxiliary magnetic field for perpendicular magnetization switching, greatly limit the advantages of SAF in neuromorphic computing. In this work, both the enhanced anomalous Hall resistance and magnetic‐field‐free perpendicular magnetization switching are achieved by using oblique sputtering to fabricate the Pt/CoPt/Ru/CoTb SAF with strong interlayer exchange coupling and magnetic moment compensation. The fabricated SAF as synapse shows nearly linear, nonvolatile multistate plasticity, and as neuron exhibits a nonlinear sigmoid activation function, which are used to construct a fully connected neural network with a remarkable 97.0–98.1% recognition rate for the handwritten digits. Additionally, SAF serving as spike‐timing‐dependent plasticity synapse is used to construct an adaptive, unsupervised learning spiking neural network, and achieve an 87.0% accuracy in handwritten digit recognition. The findings exhibit the promise of SAFs as specialized hardware for high‐performance neuromorphic computing, offering high recognition rates and low power consumption. [ABSTRACT FROM AUTHOR]

Current‐induced magnetization switching via spin‐orbit torque (SOT) holds great potential for applications in high‐speed and energy‐efficient magnetic memory and logic devices. In the extensively studied heavy metal/ferromagnet (HM/FM) SOT heterostructures, the thickness of the FM layer is typically restricted to a few nanometers or less due to the rapid spin dephasing, making it challenging to implement thermally stable memory cells with high density. In this study, it is demonstrated that this thickness constraint can be significantly alleviated by utilizing an oxide ferromagnet La0.67Sr0.33MnO3 (LSMO). Through electrical transport and magnetic optical measurements, it is found that the SOT can switch the magnetization in Pt/LSMO heterostructures even at an LSMO thickness of 35 nm, which is one order of magnitude larger than that for metallic FMs, such as CoFeB. Furthermore, based on the FM thickness dependence of the switching current and the domain switching type revealed by magnetic optical Kerr effect imaging (MOKE), a possible picture is proposed to describe the SOT switching in Pt/LSMO, which highlights the critical role of the domain wall propagation in the vertical direction. The work provides valuable insights into the behavior of SOT switching in ultra‐thick FM films, offering new possibilities for their practical applications. [ABSTRACT FROM AUTHOR]

We report on the development of a "two-field-scan" harmonic Hall voltage (HHV) analysis, which collects the second HHV as a function of a swept in-plane magnetic field at 45° and 0° relative to the excitation current, for the determination of the spin-orbit torques of transverse spins in magnetic heterostructures without significant perpendicular spins, longitudinal spins, and longitudinal/perpendicular Oersted fields. We demonstrate that this two-field-scan analysis is as accurate as the well-established but time-consuming angle-scan HHV analysis even in the presence of considerable thermoelectric effects but takes more than a factor of 7 less measurement time. We also show that the fit of the HHV data from a single field scan at 0°, which is commonly employed in the literature, is not reliable because the employment of too many free parameters in the fitting of the very slowly varying HHV signal allows erroneous conclusion about the spin-orbit torque efficiencies. [ABSTRACT FROM AUTHOR]

Complementary polarized spin-transfer torque magnetic random-access memory (CPSTT-MRAM) has been proposed to address the sensing reliability issues caused by the single-ended sensing of STT-MRAM. However, it results in a three-fold increase in the free layer (FL) area compared to STT-MRAM, leading to a higher write current. Moreover, the read and write current paths in this memory are the same, thus preventing the optimization of each operation. To address these, in this study, we proposed a complementary polarized spin-orbit torque MRAM (CPSOT-MRAM), which tackles these issues through the SOT mechanism. This CPSOT-MRAM retains the advantages of CPSTT-MRAM while significantly alleviating the high write current requirement issue. Furthermore, the separation of the read and write current paths enables the optimization of each operation. Compared to CPSTT-MRAM, the proposed CPSOT-MRAM achieves a 4.0× and 2.8× improvement in write and read power, respectively, and a 20% reduction in layout area. [ABSTRACT FROM AUTHOR]

Abstract The spin Hall efficiency (ξ) is a crucial parameter that evaluates the charge‐to‐spin conversion capability of a material, and thus materials with higher ξ are highly desirable in spin–orbit torque (SOT) devices. Recent studies have highlighted the use of ferromagnetic materials as robust spin sources, paving the way for the development of more efficient SOT devices. To accelerate this innovation, it is essential to pursue ferromagnetic materials of high ξ. Here the experimental observation of a large spin Hall efficiency is reported in ferromagnetic Heusler alloy Co2MnAl (CMA)‐based magnetic trilayers. Utilizing the current‐induced hysteresis loop shift technique, the spin Hall efficiency is determined to be 0.077 for the B2‐phase and 0.029 for the disordered CMA. Notably, magnetization switching both with and without the application of an external auxiliary magnetic field were achieved in these trilayers. The enhancement of ξ is attributed to the formation of chemical ordering in CMA. These findings provide new avenues for the development of ferromagnet‐based SOT devices.

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Recently, topological insulators (TIs) have regained extensive attention in spintronics due to their potential applications in new‐generation spintronic devices, following the discovery of the quantum Hall effect and quantum anomalous Hall effect, which introduce the topological concept. In this review, the exotic spin transport phenomena are explored in TIs. The review offers a concise overview of the fundamental principles of TIs, followed by an exploration of diverse fabrication methods for TI materials. Characterization techniques of the topological surface states are also presented. The review delves into the intriguing spin current transport phenomena, focusing on spin‐to‐charge and charge‐to‐spin conversions in TI/ferromagnet bilayers, respectively. The review culminates summarizing key insights and project future directions for research on spin transport phenomena in TIs, emphasizing practical implications. [ABSTRACT FROM AUTHOR]

This article examines recent advances in the field of antiferromagnetic spintronics from the perspective of potential device realization and applications. We discuss advances in the electrical control of antiferromagnetic order by current-induced spin–orbit torques, particularly in antiferromagnetic thin films interfaced with heavy metals. We also review possible scenarios for using voltage-controlled magnetic anisotropy as a more efficient mechanism to control antiferromagnetic order in thin films with perpendicular magnetic anisotropy. Next, we discuss the problem of electrical detection (i.e., readout) of antiferromagnetic order and highlight recent experimental advances in realizing anomalous Hall and tunneling magnetoresistance effects in thin films and tunnel junctions, respectively, which are based on noncollinear antiferromagnets. Understanding the domain structure and dynamics of antiferromagnetic materials is essential for engineering their properties for applications. For this reason, we then provide an overview of imaging techniques as well as micromagnetic simulation approaches for antiferromagnets. Finally, we present a perspective on potential applications of antiferromagnets for magnetic memory devices, terahertz sources, and detectors. [ABSTRACT FROM AUTHOR]

Bismuth is a well-known semimetal material with strong spin–orbit coupling and has been confirmed to exhibit a larger spin Hall angle in CuBi and PtBi alloys with low Bi-doping concentration. In this study, we investigated perpendicular magnetic anisotropy (PMA) and spin–orbit torques (SOTs) in Pt/Co/Pt multilayers by inserting a Bi layer with a thickness of 2 nm at the Co/Pt interface. Two types of PMA multilayers, Pt (3 nm)/Co (1 nm)/Pt (5 nm) and Pt (3 nm)/Co (1 nm)/Pt (1 nm), with different spin accumulations, were designed and prepared by varying the top Pt thickness. A significant enhancement of PMA and SOT efficiency is observed in the Pt (3 nm)/Co (1 nm)/Bi (2 nm)/Pt (5 nm) multilayer via a Bi-layer interfacial decoration. However, for the Pt (3 nm)/Co (1 nm)/Bi (2 nm)/Pt (1 nm) multilayers, both PMA and SOT efficiency decrease with decoration of the Bi layer at the Co/Pt interface. Meanwhile, the sign of SOTs changes in the Pt (3 nm)/Co (1 nm)/Pt (5 nm) and Pt (3 nm)/Co (1 nm)/Pt (1 nm) multilayers when introducing a Bi layer. This completely opposite behavior illustrates that the Bi/Pt interface plays an important role in modulating the PMA and SOT efficiency of Pt/Co/Bi/Pt multilayers. Optimizing the alloying of Bi/Pt could be an effective approach to increase the PMA and SOT efficiency of Pt/Co/Bi/Pt multilayers. [ABSTRACT FROM AUTHOR]

The incorporation of randomness into stochastic computing can provide ample opportunities for applications such as simulated annealing, non‐polynomial hard problem solving, and Bayesian neuron networks. In these cases, a considerable number of random numbers with an accurate and configurable probability distribution function (PDF) are indispensable. Preferably, these random numbers are provided at the hardware level to improve speed, efficiency, and parallelism. In this paper, how spin‐orbit torque magnetic tunnel junctions (SOT‐MTJs) with high barriers are suitable candidates for the desired true random number generators is demonstrated. Not only do these SOT‐MTJs perform excellently in speed and endurance, but their randomness can also be conveniently and precisely controlled by a writing voltage, which makes them a well‐performed Bernoulli bit. By utilizing these SOT‐MTJ‐based Bernoulli bits, any PDF, including Gaussian, uniform, exponential, Chi‐square, and even arbitrarily defined distributions can be realized. These PDF‐configurable true random number generators can then promise to advance the development of stochastic computing and broaden the applications of the SOT‐MTJs. [ABSTRACT FROM AUTHOR]

Owing to rapid developments in spintronics, spin-based logic devices have emerged as promising tools for next-generation computing technologies. This paper provides a comprehensive review of recent advancements in spin logic devices, particularly focusing on fundamental device concepts rooted in nanomagnets, magnetoresistive random access memory, spin–orbit torques, electric-field modulation, and magnetic domain walls. The operation principles of these devices are comprehensively analyzed, and recent progress in spin logic devices based on negative differential resistance-enhanced anomalous Hall effect is summarized. These devices exhibit reconfigurable logic capabilities and integrate nonvolatile data storage and computing functionalities. For current-driven spin logic devices, negative differential resistance elements are employed to nonlinearly enhance anomalous Hall effect signals from magnetic bits, enabling reconfigurable Boolean logic operations. Besides, voltage-driven spin logic devices employ another type of negative differential resistance element to achieve logic functionalities with excellent cascading ability. By cascading several elementary logic gates, the logic circuit of a full adder can be obtained, and the potential of voltage-driven spin logic devices for implementing complex logic functions can be verified. This review contributes to the understanding of the evolving landscape of spin logic devices and underscores the promising prospects they offer for the future of emerging computing schemes. [ABSTRACT FROM AUTHOR]

The energy‐efficient spin‐orbit torque (SOT) based devices are essential for future memory and logic technologies. To realize a deterministic switching, an external in‐plane magnetic field is usually needed to break the symmetry, which becomes an obstacle for device applications. Here, a field‐free switching in a perpendicularly magnetized yttrium iron garnet covered with an oblique deposited Pt with nitrogen incorporation is demonstrated. The spin‐orbit torque efficiency is enhanced with the increasing incorporation ratio of nitrogen in Pt. The maximum effective spin Hall angle of Pt(N) can reach 0.113, which is almost two times larger than that of pure Pt in Pt/YIG. Meanwhile, the switching current density is reduced with the incorporation of nitrogen. These findings open a route toward high‐efficiency SOT driven spintronic devices based on magnetic insulators. [ABSTRACT FROM AUTHOR]

Stochasticity plays a significant role in the low‐power operation of a biological neural network. In an artificial neural network, stochasticity also contributes to critical functions such as the uncertainty quantification (UQ) for estimating the probability for the correctness of prediction. This UQ is vital for cutting‐edge applications, including medical diagnostics, autopilots, and large language models. Thanks to nonlinear variation of analogous Hall resistance with high computing velocity and low dissipation, a stochastic spin‐orbit‐torque (SOT) device exhibits significant potential for implementing the UQ. However, up until now, the application of UQ for stochastic SOT devices remains unexplored. In this study, based on SOT‐induced stochastic magnetic domain wall (DW) motion with varying velocity, a SOT synapse is fabricated that can emulate stochastic weight update following the Spike‐Timing‐Dependent‐Plasticity (STDP) rule. Furthermore, a stochastic SNN is set up, which, when compared to its deterministic counterpart, demonstrates a clear advantage in quantifying uncertainty for diagnosing the type of breast tumor (benign or malignant). [ABSTRACT FROM AUTHOR]

Antiferromagnets (AFM) hold significant promise as ideal candidates for high‐density and ultrafast memory applications. Electrical manipulation of exchange bias (EB) has emerged as an effective solution to integrate AFMs into magnetic memories as active elements. In particular, spin‐orbit torque antiferromagnetic random‐access memory (SOT‐ARAM) is recently been demonstrated by using an AFM/FM hybrid free layer, which can simultaneously satisfy field‐free switching and good device scalability. However, the switching current density of the exchange bias in SOT‐ARAM devices is still high, and novel functionalities are exploited in this device scheme. In this study, the all‐electrical manipulation of the ARAM devices through the interplay of SOT and spin‐transfer torque (STT) is reported, both in three‐terminal and two‐terminal configurations. The SOT current density achieves a 40% reduction thanks to the incorporation of the STT current. Macrospin simulations are performed to illustrate the underlying mechanism. Further, a majority gate that can be decomposed into reconfigurable AND/OR functionalities in a single ARAM device is demonstrated, with an operation speed as fast as 2 ns. The results can advance the development of high‐performance memories and in‐memory computing. [ABSTRACT FROM AUTHOR]

Spintronics, utilizing both the charge and spin of electrons, benefits from the nonvolatility, low switching energy, and collective behavior of magnetization. These properties allow the development of magnetoresistive random access memories, with magnetic tunnel junctions (MTJs) playing a central role. Various spin logic concepts are also extensively explored. Among these, spin logic devices based on the motion of magnetic domain walls (DWs) enable the implementation of compact and energy-efficient logic circuits. In these devices, DW motion within a magnetic track enables spin information processing, while MTJs at the input and output serve as electrical writing and reading elements. DW logic holds promise for simplifying logic circuit complexity by performing multiple functions within a single device. Nevertheless, the demonstration of DW logic circuits with electrical writing and reading at the nanoscale is still needed to unveil their practical application potential. In this review, we discuss material advancements for high-speed DW motion, progress in DW logic devices, groundbreaking demonstrations of current-driven DW logic, and its potential for practical applications. Additionally, we discuss alternative approaches for current-free information propagation, along with challenges and prospects for the development of DW logic. [ABSTRACT FROM AUTHOR]

Spin-orbit torque (SOT) plays an efficient and versatile role in electrical manipulation in spintronic devices at the nanoscale, which shows great promise for ultrafast and energy-efficient magnetic random-access memory (MRAM). To get high-performance SOT devices, their charge-to-spin conversion ratio must be sufficiently high and low current consumption is the desired one. Two-dimensional van der Waals (2D-vdW) materials possess strong tunability and spin-orbit coupling compared to conventional metals, which can efficiently achieve both things. This review covers a generalized introduction to SOT and its origin, their measurement techniques, SOTs observed in various 2D material-based heterostructures made of topological insulators (TIs), transition metal dichalcogenides (TMDs), and van der Waals (vdW) materials as they have excellent electronic properties down to their monolayer limit and ease of integration. Further, it covers the recent progress of SOT devices in each category, highlighting their potential for achieving high-performance and energy-efficient spintronic devices and their potential applications. [ABSTRACT FROM AUTHOR]

Spin‐orbit torque resulting from non‐magnetic materials with strong spin‐orbit coupling enables electrically controlled magnetization switching, offering potential applications in ultralow‐power memory and logic devices. However, such switching of perpendicular magnetization usually requires an in‐plane magnetic field along the applied current direction, which limits its use. To address this challenge, an all‐oxide superlattice is designed and fabricated that show both the perpendicular magneto‐crystalline anisotropy and in‐plane magnetic anisotropies induced by interfacial engineering. The results demonstrate that the coexistence of perpendicular and in plane magnetic anisotropy breaks the symmetry and thus enables the pure electrical switching of perpendicular magnetization. [ABSTRACT FROM AUTHOR]

The utilization of novel noncollinear antiferromagnetic materials holds great promise for the development of energy‐efficient spintronic devices. However, only a few studies have reported on the all‐electrical control of perpendicular magnetization switching using noncollinear antiferromagnets as the spin source, and the underlying mechanism behind the unconventional spin‐orbit torque (SOT) is still a topic of debate. In this work, deterministic perpendicular magnetization switching in Mn3Sn/CoTb bilayers is successfully achieved. Compared to the control samples with heavy metal as the spin source, the critical switching current density is over one order of magnitude reduced, indicating an enhanced efficiency of the out‐of‐plane charge‐to‐spin conversion in the textured Mn3Sn films. The influence of film thickness and growth temperature on the efficiency of different spin polarizations suggests potential roles of crystal quality and spin texture in spin diffusion with different spin polarization directions. These findings provide valuable insights into the crystal structure, spin‐orbit torque effects, and charge‐to‐spin conversion in Mn3Sn films, highlighting the importance of understanding interface and bulk contributions in antiferromagnetic spin transport phenomena. [ABSTRACT FROM AUTHOR]

To decrease the energy consumption for the electrical manipulation of magnetization, the enhancement of the spin Hall effect through alloying is widely investigated, but the use of rare earth elements is rarely mentioned. This work reports the modification of the spin Hall effect on Pt by doping rare earth Tb atoms. The spin–orbit torque (SOT) performance is significantly enhanced in Pt100‐yTby alloyed heavy metal (HM) layer. Compared with the Tb‐free sample, the damping‐like effective field per unit current density increases to 1.9 times in the samples with Tb content between 5% and 10%. The critical current density for magnetization reversal is greatly reduced by 65% in a device with Pt87Tb13 HM layer and the in‐plane assistant field as small as ±20 Oe is sufficient for the deterministic switching in the same device. By magneto‐optical Kerr effect imaging, it is confirmed that the increased in‐plane field can effectively compensate the Dzyaloshinskii–Moriya interaction (DMI), which not only helps to reduce the critical current, but also facilitates the domain wall motion and is beneficial for the switching process. All results show that the Pt‐Tb alloy is a competitive candidate for low‐power spintronic devices. [ABSTRACT FROM AUTHOR]

The spin Hall effect enables fast and reliable writing operations for next‐generation spin‐orbit‐torque magnetoresistive random‐access memories (SOT‐MRAMs). To develop SOT‐MRAMs; however, the spin Hall material should have a sufficiently low writing energy and high annealing stability for the semiconductor integration process. Thus far, none of the crystalline‐based spin Hall materials are able to satisfy these requirements. Here, a promising solution for SOT‐MRAMs is provided using amorphous W─Ta─B alloys. Even without a long‐range crystal order, W─Ta─B alloys exhibit both large effective spin Hall angles up to 40% derived from a Ta substitutional doping and superior annealing stability (up to 400 °C) due to the addition of B, enabling them to satisfy both requirements. Nanoscale three‐terminal SOT‐MRAM cells are fabricated, and these are demonstrated to have high magnetoresistance ratios (up to 130%) and extremely low intrinsic switching current densities (down to 4 × 106 A cm−2). These results show that amorphous spin Hall materials can provide the key for realizing high‐performance SOT‐MRAMs. [ABSTRACT FROM AUTHOR]

Abstract Antiferromagnets (AFM) hold significant promise as ideal candidates for high‐density and ultrafast memory applications. Electrical manipulation of exchange bias (EB) has emerged as an effective solution to integrate AFMs into magnetic memories as active elements. In particular, spin‐orbit torque antiferromagnetic random‐access memory (SOT‐ARAM) is recently been demonstrated by using an AFM/FM hybrid free layer, which can simultaneously satisfy field‐free switching and good device scalability. However, the switching current density of the exchange bias in SOT‐ARAM devices is still high, and novel functionalities are exploited in this device scheme. In this study, the all‐electrical manipulation of the ARAM devices through the interplay of SOT and spin‐transfer torque (STT) is reported, both in three‐terminal and two‐terminal configurations. The SOT current density achieves a 40% reduction thanks to the incorporation of the STT current. Macrospin simulations are performed to illustrate the underlying mechanism. Further, a majority gate that can be decomposed into reconfigurable AND/OR functionalities in a single ARAM device is demonstrated, with an operation speed as fast as 2 ns. The results can advance the development of high‐performance memories and in‐memory computing.

Abstract Stochasticity plays a significant role in the low‐power operation of a biological neural network. In an artificial neural network, stochasticity also contributes to critical functions such as the uncertainty quantification (UQ) for estimating the probability for the correctness of prediction. This UQ is vital for cutting‐edge applications, including medical diagnostics, autopilots, and large language models. Thanks to nonlinear variation of analogous Hall resistance with high computing velocity and low dissipation, a stochastic spin‐orbit‐torque (SOT) device exhibits significant potential for implementing the UQ. However, up until now, the application of UQ for stochastic SOT devices remains unexplored. In this study, based on SOT‐induced stochastic magnetic domain wall (DW) motion with varying velocity, a SOT synapse is fabricated that can emulate stochastic weight update following the Spike‐Timing‐Dependent‐Plasticity (STDP) rule. Furthermore, a stochastic SNN is set up, which, when compared to its deterministic counterpart, demonstrates a clear advantage in quantifying uncertainty for diagnosing the type of breast tumor (benign or malignant).

Abstract The energy‐efficient spin‐orbit torque (SOT) based devices are essential for future memory and logic technologies. To realize a deterministic switching, an external in‐plane magnetic field is usually needed to break the symmetry, which becomes an obstacle for device applications. Here, a field‐free switching in a perpendicularly magnetized yttrium iron garnet covered with an oblique deposited Pt with nitrogen incorporation is demonstrated. The spin‐orbit torque efficiency is enhanced with the increasing incorporation ratio of nitrogen in Pt. The maximum effective spin Hall angle of Pt(N) can reach 0.113, which is almost two times larger than that of pure Pt in Pt/YIG. Meanwhile, the switching current density is reduced with the incorporation of nitrogen. These findings open a route toward high‐efficiency SOT driven spintronic devices based on magnetic insulators.

Spintronic devices have become a crucial technology for overcoming the power consumption bottleneck in integrated circuits, due to their low power consumption, high-speed processing capability. Two-dimensional materials offer potential for performance enhancement and device miniaturization in spintronics because of their unique electronic and spin properties. Specifically, two-dimensional transition metal dichalcogenides (2D TMDs) are favored in the field of spintronics for their strong spin–orbit coupling effects, enabling effective control over the electron spin state. However, the preparation techniques for 2D TMDs are still in the exploratory stage. In this work, we explore novel preparation method combining magnetron sputtering and molecular beam epitaxy, leading to wafer-scale high-quality monocrystalline PtTe2 thin films. Further, Spin-Orbit Torque (SOT) efficiency is investigated in PtTe2-based heterostructures, which reveals a significant spin Hall angle of over 0.094. Our work provides a new way to fabricate the wafer-scale PtTe2 thin films and confirms a large SOT efficiency, which indicates the great promise for spintronic applications.

Abstract To decrease the energy consumption for the electrical manipulation of magnetization, the enhancement of the spin Hall effect through alloying is widely investigated, but the use of rare earth elements is rarely mentioned. This work reports the modification of the spin Hall effect on Pt by doping rare earth Tb atoms. The spin–orbit torque (SOT) performance is significantly enhanced in Pt100‐yTby alloyed heavy metal (HM) layer. Compared with the Tb‐free sample, the damping‐like effective field per unit current density increases to 1.9 times in the samples with Tb content between 5% and 10%. The critical current density for magnetization reversal is greatly reduced by 65% in a device with Pt87Tb13 HM layer and the in‐plane assistant field as small as ±20 Oe is sufficient for the deterministic switching in the same device. By magneto‐optical Kerr effect imaging, it is confirmed that the increased in‐plane field can effectively compensate the Dzyaloshinskii–Moriya interaction (DMI), which not only helps to reduce the critical current, but also facilitates the domain wall motion and is beneficial for the switching process. All results show that the Pt‐Tb alloy is a competitive candidate for low‐power spintronic devices.

Abstract The utilization of novel noncollinear antiferromagnetic materials holds great promise for the development of energy‐efficient spintronic devices. However, only a few studies have reported on the all‐electrical control of perpendicular magnetization switching using noncollinear antiferromagnets as the spin source, and the underlying mechanism behind the unconventional spin‐orbit torque (SOT) is still a topic of debate. In this work, deterministic perpendicular magnetization switching in Mn3Sn/CoTb bilayers is successfully achieved. Compared to the control samples with heavy metal as the spin source, the critical switching current density is over one order of magnitude reduced, indicating an enhanced efficiency of the out‐of‐plane charge‐to‐spin conversion in the textured Mn3Sn films. The influence of film thickness and growth temperature on the efficiency of different spin polarizations suggests potential roles of crystal quality and spin texture in spin diffusion with different spin polarization directions. These findings provide valuable insights into the crystal structure, spin‐orbit torque effects, and charge‐to‐spin conversion in Mn3Sn films, highlighting the importance of understanding interface and bulk contributions in antiferromagnetic spin transport phenomena.

Recently, vast research has been under investigation on the role of chirality in magnetization dynamics, an area that currently lacks a comprehensive understanding. To gain further insight into the importance of chirality, we explore the effects of varying the degree of chirality. To investigate these effects, we have fabricated samples with perpendicular magnetic anisotropy symmetry breaking through local helium ion irradiation with various azimuthal angles and degrees of irradiation. In this system, the spin-orbit torque can induce artificial spin texture, and our azimuthal angle and degree of chirality dependent results reveal a clear cosine dependence and a nonlinear increase, respectively. It implies the system not only follows the energy contribution of interfacial Dzyaloshinskii-Moriya interaction but also has a nonlinear impact depending on anisotropy asymmetry induced chirality differences. These experimental observations are consistent with our theoretical model and micromagnetic simulations, supporting our experimental results. Overall, our findings provide further insights into the role of chirality in magnetization dynamics and may have important implications for the development of future magnetic devices.

Abstract The spin Hall effect enables fast and reliable writing operations for next‐generation spin‐orbit‐torque magnetoresistive random‐access memories (SOT‐MRAMs). To develop SOT‐MRAMs; however, the spin Hall material should have a sufficiently low writing energy and high annealing stability for the semiconductor integration process. Thus far, none of the crystalline‐based spin Hall materials are able to satisfy these requirements. Here, a promising solution for SOT‐MRAMs is provided using amorphous W─Ta─B alloys. Even without a long‐range crystal order, W─Ta─B alloys exhibit both large effective spin Hall angles up to 40% derived from a Ta substitutional doping and superior annealing stability (up to 400 °C) due to the addition of B, enabling them to satisfy both requirements. Nanoscale three‐terminal SOT‐MRAM cells are fabricated, and these are demonstrated to have high magnetoresistance ratios (up to 130%) and extremely low intrinsic switching current densities (down to 4 × 106 A cm−2). These results show that amorphous spin Hall materials can provide the key for realizing high‐performance SOT‐MRAMs.

With the growing demand for high‐speed electronic devices with low energy consumption, spin–orbit torque (SOT) has become a significant focus. SOT can switch the magnetization direction in a material system with broken inversion symmetry, such as a normal metal (NM)/ferromagnet (FM) heterojunction. The SOT consists of two mutually orthogonal vector components along with the injected current direction: the transverse damping‐like torque (DLT) and the longitudinal field‐like torque (FLT). Numerous studies have mainly centered on the DLT for the SOT switching mechanism. However, DLT and FLT are essential to enhance SOT efficiency because FLT boosts the magnetization precession motion. Herein, heterojunctions consisting of NM 1 (Ta, W, or Pt)/NM 2 (Nb)/FM (CoFeB) are devised to manipulate the FLT‐to‐DLT ratio (η) through the change in Nb thickness. Furthermore, experimental confirmation exists for reducing threshold current as η increases. The SOT devices with substantial η generate random numbers. The National Institute of Standards and Technology Special Publication 800‐90B test verifies randomness and confirms that the SOT devices are beneficial sources for true random number generators (TRNGs). These findings indicate the crucial role of FLT in the SOT switching process and underscore its significance in developing SOT‐based TRNG devices. [ABSTRACT FROM AUTHOR]

Spintronic devices are driving new paradigms of bio-inspired, energy efficient computation like neuromorphic stochastic computing and in-memory computing. They have also emerged as key candidates for non-volatile memories for embedded systems as well as alternatives to persistent memories. To meet the growing demands from such diverse applications, there is need for innovation in materials and device designs which can be scaled and adapted according to the application. Two-dimensional (2D) magnetic materials address challenges facing bulk magnet systems by offering scalability while maintaining device integrity and allowing efficient control of magnetism. In this review, we highlight the progress made in experimental studies on 2D magnetic materials towards their integration into spintronic devices. We provide an account of the various relevant material discoveries, demonstrations of current and voltage-based control of magnetism and reported device systems, while also discussing the challenges and opportunities towards integration of 2D magnetic materials in commercial spintronic devices. [ABSTRACT FROM AUTHOR]