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a,b) Schematics of the MTJ unit cell in MRAM, which is based on STT‐induced switching: a) two terminal STT‐MRAM and SOT‐induced switching: b) three terminal STT‐MRAM, respectively. The arrows in the layers indicate the direction of the magnetic moments. Illustrations of SOT generating mechanisms in NM/FM bilayers c) bulk SHE from NM and d) interfacial REE from the NM/FM interface. Blue and red arrows represent the direction of spin polarization σ. Green arrows indicate magnetization (M) direction of the FM layer. E corresponds to the electric field induced by the inversion asymmetry. e) Direction of DLT (red arrow) and FLT (blue arrow). Green arrows indicate magnetization (M) direction of the FM layer.
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Control of magnetization in magnetic nanostructures is essential for development of spintronic devices because it governs fundamental device characteristics such as energy consumption, areal density, and operation speed. In this respect, spin–orbit torque (SOT), which originates from the spin–orbit interaction, has been widely investigated due to i...
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... Such advances could contribute significantly to the evolution of the microelectronics and information technology sector. [18][19][20] The OHE, intrinsic to any material with finite electron angular momentum, is an inherent property. Theoretical estimations indicate that the values for the orbital Hall conductivity ( ) are notably larger than those of spin Hall conductivity ( ). 13,21 As a result, both the orbital Hall effect and its inverse counterpart, the inverse orbital Hall effect (IOHE), exhibit stronger effects compared to the intrinsic spin Hall effect and its inverse, the inverse spin Hall effect (ISHE). ...
... We attribute this unconventional angular dependence to the nonlinear current dependence of SOT, emphasizing its relevance to understand the magnetization dynamics during SOT-induced switching under large currents. 3 Spin-orbit torque (SOT), a type of spin torque caused by spin-orbit coupling-induced spin currents [1][2][3] , enables the efficient electrical manipulation of magnetization in various spintronic devices. In particular, SOT provides a fast and energy-efficient means by which to realize current-induced magnetization switching 4,5 and domain wall motion 6,7 , both of which can be exploited for magnetic random-access memory 8,9 , spin Hall nano-oscillators 10,11 , true random number generators 12 , magnonic devices 13 , and neuromorphic computing devices 14 , among others. ...
... We attribute this unconventional angular dependence to the nonlinear current dependence of SOT, emphasizing its relevance to understand the magnetization dynamics during SOT-induced switching under large currents. 3 Spin-orbit torque (SOT), a type of spin torque caused by spin-orbit coupling-induced spin currents [1][2][3] , enables the efficient electrical manipulation of magnetization in various spintronic devices. In particular, SOT provides a fast and energy-efficient means by which to realize current-induced magnetization switching 4,5 and domain wall motion 6,7 , both of which can be exploited for magnetic random-access memory 8,9 , spin Hall nano-oscillators 10,11 , true random number generators 12 , magnonic devices 13 , and neuromorphic computing devices 14 , among others. ...
... shows the current dependence of the coefficients 2 ( = 1, 3, 5, 7) in 2 at a = 25 Oe obtained by fitting the 2 data to Eq. (2). We found that the signs of3 2 , of the SOT effective fields. The details about 1 and 2 are found in Supplementary Information 1. ...
Spin orbit torque (SOT), arising from spin-orbit coupling-induced spin currents, provides efficient control of the magnetization direction. SOT characterization that involves analyzing the first and second harmonic Hall resistances are typically done in a low-current regime, distinct from a high-current regime, where SOT-induced magnetization switching occurs. In this study, we investigate the azimuthal angle ( ϕ )-dependent harmonic Hall resistances of a Pt/yttrium iron garnet (YIG) layer across a wide range of measurement currents. Under low-current conditions, conventional ϕ-dependent Hall resistances are observed; the first harmonic Hall resistance exhibits sin2 ϕ behavior and the second harmonic Hall resistance comprises cos ϕ and cos3 ϕ terms, associated with damping-like and field-like SOT, respectively. Interestingly, with an increase in the current, higher-order angular-dependent terms become non-negligible, referring to the sin4 ϕ and sin6 ϕ terms for the first harmonic and the cos5 ϕ and cos7 ϕ terms for the second harmonic Hall resistances. We attribute this unconventional angular dependence to the nonlinear current dependence of SOT, emphasizing its relevance to understand the magnetization dynamics during SOT-induced switching under large currents.
... The electron spins with a specific direction penetrate the FM layer and can transfer angular momentum and some torques to the magnetization vector of the FM layer, ultimately forced the FM layer magnetized along its direction. This phenomenon is called spin-orbit torque (SOT) [19][20][21][22][23]. In this article, we try to investigate a transverse magneto-optical Kerr effect (TMOKE) by manipulating the magnetization of the ferromagnetic layer with the SOT process. ...
In this study, we propose and simulate a magnetoplasmonics heterostructure that utilizes spin-orbit fields to generate an internal magnetic field and create a significant magneto-optical effect. Our approach offers a new way to overcome the challenges of using permanent magnets or magnetic coils in conventional magnetoplasmonics, such as high-power consumption and non-scalability. We demonstrate that it is possible to create an appropriate amount of magnetic field using spin-orbit fields induced by the spin-Hall effect, such that the consumption power becomes reasonable and the dimensions could be miniaturized. This approach will be an important development in the field of magneto-optics, as it can lead to enhanced transverse magneto-optical Kerr effect in the present of surface plasmon polaritons. The proposed nanostructure consists of a ferromagnetic film adjacent to a heavy metal layer, both sandwiched between two noble metal films, and deposited on a dielectric prism. The strength of the Kerr signal strongly depends on the thickness of the ferromagnetic layer, with the maximum effect observed at a thickness of 5nm. This concept has potential for various nanophotonic and spintronic applications, particularly for developing high-speed active plasmonic devices for ultrafast light modulation.
... The study of magnetization manipulation in heavy metal (HM)/ferromagnetic material (FM) heterostructures via spinorbit torque (SOT) has attracted strong interest as there * Authors to whom any correspondence should be addressed. is huge potential for further development into new highperformance and energy-efficient magnetic memories, logic devices, oscillators, and non-conventional computing devices [1][2][3][4][5]. Furthermore, when a beam passes through an optical interface or a non-uniform medium, the photons undergo transverse spin splitting concerning the geometrical optical trajectory, called the photon spin Hall effect (SHE) [6,7]. ...
High effective spin Hall efficiency and low magnetic damping constant are essential to achieve efficient spin-charge conversion for energy-efficient spintronic devices. We report the measurements of effective spin Hall efficiency and magnetic damping constant of Pt1-xTax/CoFeB structures using spin-torque ferromagnetic resonance (ST-FMR) techniques. With the increase of Ta content, the spin Hall efficiency increases and peaks x = 0.15 with the value of θ_SH^eff=0.35, before decreases for further Ta content. This non-monotonic variation is attributed to the interaction between the contribution of the extrinsic skew scattering mechanism and the spin-orbit coupling. The weakening of the spin-orbit coupling in Pt1-xTax layer leads to a decrease in the effective magnetic damping constant with increasing Ta concentration. High-temperature ST-FMR measurements confirm the influence of the Ta concentration on the spin Hall effect and magnetic damping mechanism. Additionally, the decrease in spin mixing conductance and the increase in spin diffusion length leads to a decrease in the interfacial spin transparency.
... The SOT consists of two mutually orthogonal vector components: damping-like torque (DLT, τ DLT ¼m  ðm ÂŝÞ) and field-like torque (FLT, τ FLT ¼m Âŝ), wherem andŝ are unit vectors of magnetization and spin polarization. [9][10][11][12][13][14][15][16][17][18] This study explores the potential of SOT devices with perpendicular magnetic anisotropy (PMA) as a foundation for true random number generators (TRNGs) based on stochastic physics. The DLT aligns the magnetization along the y-direction. ...
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.
... Quantifying the strength of the SOT has become a critical issue in spintronics research, as it is directly related to the efficiency of device operation [19][20][21][22] . To this end, various measurement methods have been proposed. ...
... These accumulated spins are injected into the CoFeB layer, which is called spin pumping. The pumped spin induces damping-like SOT and field-like SOT 22 . Both SOTs act www.nature.com/scientificreports/ ...
Controlling the direction of magnetization with an electric current, rather than a magnetic field, is a powerful technique in spintronics. Spin–orbit torque, which generates an effective magnetic field from the injected current, is a promising method for this purpose. Here we show an approach for quantifying the magnitude of spin–orbit torque from a single magnetic image. To achieve this, we deposited two concentric electrodes on top of the magnetic sample to flow a radial current. By counterbalancing the current effect with an external magnetic field, we can create a stable circular magnetization state. We measure the magnitude of spin–orbit torque from the stable radius, providing a new tool for characterizing spin–orbit torque.
... Since there have been very good reviews on perpendicular anisotropy, [15] spin-orbit torques, [16][17][18][19][20][21]22,23] domain wall motion, [24] and other more generalized aspects, [25] this review will focus on recent advances in the understanding of the electrical generation of spin current, the switching mechanisms and the switching strategies of perpendicular magnetization, the switching current density by the spin-orbit torques of transverse spins, choice of perpendicular magnetic materials, perpendicular SOT memory devices, perpendicular SOT logic devices, and finally conclusion and perspective. ...
Magnetic materials with strong perpendicular magnetic anisotropy are of great interest for the development of nonvolatile magnetic memory and computing technologies due to their high stabilities at the nanoscale. However, electrical switching of such perpendicular magnetization in an energy‐efficient, deterministic, scalable manner has remained a big challenge. This problem has recently attracted enormous efforts in the field of spintronics. Here, we review recent advances and challenges in the understanding of the electrical generation of spin currents, the switching mechanisms and the switching strategies of perpendicular magnetization, the switching current density by spin‐orbit torque of transverse spins, the choice of perpendicular magnetic materials, and summarize the progress in prototype perpendicular SOT memory and logic devices toward the goal of energy‐efficient, dense, fast perpendicular spin‐orbit torque applications.
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... Among the various mechanisms explored, spin-orbit torque (SOT), in which a spin current can exert a torque on the magnetization of a ferromagnetic material, has emerged as the most attractive method for efficient electrical control of magnetism. [1][2][3][4] This torque can be used to switch the magnetization of the material, which has potential applications in spintronic devices, such as magnetic random access memories (MRAMs) and logic gates. [5][6][7][8][9][10][11] The discovery of SOT can be traced back to the investigation of a crystalline (Ga, Mn)As diluted ferromagnetic semiconductor (DFMS) film. ...
We investigated the spin–orbit torque (SOT) switching mechanism of a single layer of crystalline diluted ferromagnetic semiconductor by simulating the current scan hysteresis using the Landau–Lifshitz–Gilbert equation. Our study focuses on the switching of the out-of-plane magnetization component during current scans to provide a detailed understanding of the SOT switching process. The simulation results reveal that the SOT switching strongly depends on the relative strengths of the damping-like torque (DLT) and field-like torque (FLT). Through a systematic analysis, we found that the DLT to FLT ratio required for full SOT switching of the out-of-plane magnetized (GaMn)(AsP) film falls within the range of 0.5–1.0. We also identified a relationship between the DLT to FLT ratio and the linear behavior of the
out-of-plane component of magnetization during current scans under a strong in-plane bias field. This suggests that the DLT to FLT ratio of a ferromagnetic film can be directly determined from current scan measurements under a large external field, providing crucial information for developing SOT-based devices.
... Furthermore, heavy-metal (e.g., Pt, Ta, W)/ferromagnet bilayers have been extensively investigated because the spin currents generated in the heavy metal exert spin-orbit torque (SOT) on the ferromagnet and control its magnetization direction. SOT is being developed as a novel writing technology for energy-efficient MRAM [42][43][44][45]. Among such heavy elements, Pt is considered an excellent SOT material owing to its low resistivity and relatively large spin Hall angle, offering a distinct advantage in terms of power consumption for SOT-based spintronic devices over other spin-current source materials. ...
This study investigates the effects of annealing on the tunnel magnetoresistance (TMR) ratio in CoFeB/MgO/CoFeB-based magnetic tunnel junctions (MTJs) with different capping layers and correlates them with microstructural changes. It is found that the capping layer plays an important role in determining the maximum TMR ratio and the corresponding annealing temperature (Tann). For a Pt capping layer, the TMR reaches ~95% at a Tann of 350 °C, then decreases upon a further increase in Tann. A microstructural analysis reveals that the low TMR is due to severe intermixing in the Pt/CoFeB layers. On the other hand, when introducing a Ta capping layer with suppressed diffusion into the CoFeB layer, the TMR continues to increase with Tann up to 400 °C, reaching ~250%. Our findings indicate that the proper selection of a capping layer can increase the annealing temperature of MTJs so that it becomes compatible with the complementary metal-oxide-semiconductor backend process.
... This has been demonstrated to allow for high-efficiency SOT-driven magnetic switching in three-dimensional (3D) ferromagnet at room temperature with low critical switching current 17,[25][26][27][28] . However, 3D ferromagnets would limit the size scaling and lower the spin transparency due to the dangling bonding interface 29 . Therefore, there is a need to develop new material systems with lower dimensions and superior interfaces for higher SOT efficiency [30][31][32] , which may bring new opportunities to break the power consumption bottleneck of integrated circuits 33 . ...
... These results obtained with the same characterization method may provide evidence that the interfacial spin transparency could be significantly enhanced by the vdW-gapped interface between Bi 2 Te 3 and FGT due to the optimized growth method. In such a case, the ξ DL is related to the internal θ SH of TI and the interfacial spin transparency T int 29,46 . The interfacial spin transparency could be mainly determined by the mechanisms of spin backflow and spin memory loss, which could be characterized by the effective spin-mixing conductance and the spin conductance of the non-ferromagnetic layer 29 . ...
... In such a case, the ξ DL is related to the internal θ SH of TI and the interfacial spin transparency T int 29,46 . The interfacial spin transparency could be mainly determined by the mechanisms of spin backflow and spin memory loss, which could be characterized by the effective spin-mixing conductance and the spin conductance of the non-ferromagnetic layer 29 . A good interface contributes to the transparency during spin transport at room temperature, which is one of the most important factors in achieving energy-efficient SOT switching in an all-vdW heterostructure and highlights the strong SOC characteristics of TI. ...
Two-dimensional (2D) ferromagnetic materials with unique magnetic properties have great potential for next-generation spintronic devices with high flexibility, easy controllability, and high heretointegrability. However, realizing magnetic switching with low power consumption at room temperature is challenging. Here, we demonstrate the room-temperature spin-orbit torque (SOT) driven magnetization switching in an all-van der Waals (vdW) heterostructure using an optimized epitaxial growth approach. The topological insulator Bi 2 Te 3 not only raises the Curie temperature of Fe 3 GeTe 2 (FGT) through interfacial exchange coupling but also works as a spin current source allowing the FGT to switch at a low current density of ~2.2×10 ⁶ A/cm ² . The SOT efficiency is ~2.69, measured at room temperature. The temperature and thickness-dependent SOT efficiency prove that the larger SOT in our system mainly originates from the nontrivial topological origin of the heterostructure. Our experiments enable an all-vdW SOT structure and provides a solid foundation for the implementation of room-temperature all-vdW spintronic devices in the future.
