Current-induced Spin Research Articles

Current-induced spin polarization and spin Hall effect in III-V compounds two-dimensional materials

Current-induced spin polarization and spin Hall effect in III-V compounds two-dimensional materials

Transport through a monolayer-tube junction: Sheet-to-tube spin current

We develop a method to calculate the electron flow between an arbitrary atomic monolayer sheet and an arbitrary tube by expressing the corresponding sheet-tube tunneling matrix elements with those between sheets. We use this method to calculate the spin current from a monolayer silicene sheet with sublattice-staggered current-induced spin polarization to a silicene tube. The calculated sheet-to-tube spin current exhibits an oscillation as a function of the tube circumferential length because the Fermi points in the tube cross the Fermi circle in the sheet. Furthermore, the spin current with spin in the out-of-plane direction, which is absent in the sheet-sheet junction (including twisted sheets) with C3 rotational symmetry, appears in an oscillating form in the tube-sheet junction due to the broken C3 rotational symmetry. This is an example of the symmetry manipulation which realizes switching a particular component of the spin current.

High switching ratio of antiferromagnetic order in thick sputtered Mn3+xSn1−x films by spin–orbit torque

Electrical manipulation of the antiferromagnetic states of Weyl semimetal Mn3Sn by current-induced spin–orbit torque (SOT) has attracted intensive attention recently, largely due to its potential advantage for high-density integration and ultrafast operation. In this study, the relation between the antiferromagnetic SOT switching ratio and the composition of Mn3+xSn1−x films was explored systematically. While SOT manipulation of ferromagnetic order has traditionally been confined to films just a few nanometers in thickness, our results indicate that current-induced SOT can effectively switch the antiferromagnetic order of sputtered Mn3+xSn1−x films with a thickness of up to 100 nm. Notably, a high electrical switching ratio of 83% was obtained in the optimized film with a composition of Mn3.1Sn0.9. The switching of the octupole polarization in thick Mn3Sn films may be accounted for by a seeded SOT mechanism. Joule heating of the Mn3Sn film close to the Néel temperature plays a key role in this switching process. Additionally, the factors influencing the switching ratio were further investigated. This work will deepen our understanding of the electrical switching mechanism of non-collinear antiferromagnetic order in Mn3Sn film and promote the development of antiferromagnetic spintronic devices.

Prospects for Antiferromagnetic Spintronic Devices

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.

Unraveling the dynamics of magnetization in topological insulator-ferromagnet heterostructures via spin-orbit torque

Spin–orbit coupling is a relativistic effect coupling the orbital angular momentum with the spin, which determines the physical properties of condensed matter. For instance, the spin–orbit coupling strongly influences spin dynamics, opening the possibility for promising applications. The topological insulator–ferromagnet heterostructure is a typical example exhibiting spin dynamics driven by current-induced spin–orbit torque. Recent observations of the sign flip of Hall conductivity imply that the spin–orbit torque is strong enough to flip magnetization within this heterostructure. Motivated by this, our study elucidates the conditions governing spin flips by studying the magnetization dynamics. We establish that the interplay between spin-anisotropy and spin–orbit torque plays a crucial role in the magnetization dynamics. Furthermore, we categorize various modes of magnetization dynamics, constructing a comprehensive phase diagram across distinct energy scales, damping constants, and applied frequencies. We also consider the effect of a magnetic field on the magnetization dynamics. This research not only offers insights into controlling spin direction but also charts a new pathway to the practical application of spin–orbit coupled systems.

Enhancement of spin Hall angle in semimetallic materials α -Sn under voltage regulation

Utilizing current-induced spin–orbit torque (SOT) to control magnetization is essential for the advancement of spintronics. SOT offers high energy efficiency and rapid operation speed. The ideal SOT material should have a high charge-to-spin conversion efficiency and excellent electrical conductivity. Recently, there has been a focus on topological insulator materials with topological surface states in SOT research due to their controllability in spin–orbit coupling, conductivity, and energy band topology. While topological Dirac semimetallic materials show promise for SOT applications, research on voltage regulation of their spin Hall angle is still in its early stages. This paper investigates the multilayer structure of a Dirac semimetallic material. In an α-Sn/Ag bilayer, the voltage regulation effect can increase the spin Hall angle by five times by adjusting the strain on the Fermi level. Experiments explore the role of a silver layer as a transport layer in the electric field control of multilayer films. This material system can enhance its effects under electric field regulation and offer insight for achieving regulation in new spintronic devices.

Two-dimensional chiral perovskites with large spin Hall angle and collinear spin Hall conductivity.

Two-dimensional hybrid organic-inorganic perovskites with chiral spin texture are emergent spin-optoelectronic materials. Despite the wealth of chiro-optical studies on these materials, their charge-to-spin conversion efficiency is unknown. We demonstrate highly efficient electrically driven charge-to-spin conversion in enantiopure chiral perovskites (R/S-MB)2(MA)3Pb4I13 (〈n〉 = 4), where MB is 2-methylbutylamine, MA is methylamine, Pb is lead, and I is iodine. Using scanning photovoltage microscopy, we measured a spin Hall angle θsh of 5% and a spin lifetime of ~75 picoseconds at room temperature in 〈n〉 = 4 chiral perovskites, which is much larger than its racemic counterpart as well as the lower 〈n〉 homologs. In addition to current-induced transverse spin current, the presence of a coexisting out-of-plane spin current confirms that both conventional and collinear spin Hall conductivities exist in these low-dimensional crystals.

Reciprocity Relations for Mechanically Induced Spin Currents in Metals in a Nonlinear Regime

Reciprocity Relations for Mechanically Induced Spin Currents in Metals in a Nonlinear Regime

Direct observation of current-induced nonlinear spin torque in Pt-Py bilayers

Direct observation of current-induced nonlinear spin torque in Pt-Py bilayers

Perpendicular magnetic properties and field-free current-induced switching in W/CoFeB/MgO trilayers with a compensating oblique W underlayer

Zero-field magnetization switching (ZFS) driven by current-induced spin–orbit torque (SOT) holds significant importance in spintronic applications. The introduction of a lateral asymmetric structure (LAS) through oblique deposition proves to be an effective strategy for breaking inversion symmetry, thereby enabling SOT-driven ZFS. However, the coexistence of wedge thickness structure and slanted columnar microstructure in the obliquely deposited films poses challenges in distinguishing their respective effects. In this study, we conducted a comparative investigation of the perpendicular magnetic properties and current-induced switching in W/Co40Fe40B20/MgO films by oblique sputtering of the W underlayer at a fixed tilting angle and at two opposite tilting angles with its wedge thickness compensated. We have found that the perpendicular magnetic properties of the Co40Fe40B20 layer are significantly altered at large tilting angles, irrespective of whether the W wedge thickness is compensated. Notably, at a tilting angle of 50°, ZFS is realized for both the conventional oblique sample and the compensating oblique sample, with the switching polarity contingent on the final tilting direction of the W layer. We have identified a gradient in perpendicular magnetic anisotropy in these samples, attributed to the laterally varying roughness associated with the slanted columnar microstructure of the W underlayer. This study underscores the dominant role of microscopic LAS in obliquely deposited films in breaking SOT symmetry. Our research sheds light on the impact of the slanted columnar microstructure on the magnetic and magneto-transport properties of films, offering valuable insights for advancing spintronic device research.

Current-induced spin polarization in chiral tellurium: A first-principles quantum transport study

Current-induced spin polarization in chiral tellurium: A first-principles quantum transport study

Growth of thin-film magnetic nanostructures promising for spintronics applications

Multilayered metallic nanostructures are promising for the fabrication of spin valves based on the giant magnetoresistive effect and for studies of the nature of topological magnetism, aimed at the development of new nanoscale data storage and transfer devices, e.g. those based on magnetic skyrmions. It is still an important task to develop methods of synthesis and configuration of thin-film nanostructures and control of spin textures in those nanostructures under electric and spin currents generated as a result of the spin Hall effect in external electric fields. Thin-film polycrystalline ferromagnetic / heavy metal Ru(10nm)/Co(0,8)/Ru(2), Ru(10)/Co(0,8)/Ru(2)/W(4), Pt(5)/Co(0,8)/MgO(2)/Pt(2) and Pt(15)/Co(0,8)/MgO(2)/Pt(2) nanostructures have been synthesized using magnetron sputtering. Electric contacts and Hall structures with different conductive bridge thicknesses have been synthesized on the specimens using electron beam photolithography. Experimental vibration magnetometric data have been utilized to calculate magnetic parameters of the specimens, i.e., saturation magnetization, magnetic anisotropy energy and field and coercive force as functions of ferromagnetic and heavy metal layer types. The domain structure of the specimens has been studied using Kerr microscopy. The electrical resistivity has been simulated and the critical current and current density of the nanostructures have been assessed. We show that all the film specimens exhibit perpendicular magnetic anisotropy and can be used in the studies of current-induced phenomena and spin moment transfer processes in nanostructures.

Field-free spin–orbit torque switching in ferromagnetic trilayers at sub-ns timescales

Current-induced spin torques enable the electrical control of the magnetization with low energy consumption. Conventional magnetic random access memory (MRAM) devices rely on spin-transfer torque (STT), this however limits MRAM applications because of the nanoseconds incubation delay and associated endurance issues. A potential alternative to STT is spin-orbit torque (SOT). However, for practical, high-speed SOT devices, it must satisfy three conditions simultaneously, i.e., field-free switching at short current pulses, short incubation delay, and low switching current. Here, we demonstrate field-free SOT switching at sub-ns timescales in a CoFeB/Ti/CoFeB ferromagnetic trilayer, which satisfies all three conditions. In this trilayer, the bottom magnetic layer or its interface generates spin currents with polarizations in both in-plane and out-of-plane components. The in-plane component reduces the incubation time, while the out-of-plane component realizes field-free switching at a low current. Our results offer a field-free SOT solution for energy-efficient scalable MRAM applications.

Electric Field Switching of Magnon Spin Current in a Compensated Ferrimagnet.

Manipulation of directional magnon propagation, known as magnon spin current, is essential for developing magnonic devices featuring nonvolatile functionalities and ultralow power consumption. Magnon spin current can usually be modulated by magnetic field or current-induced spin torques. However, these approaches may lead to energy dissipation due to Joule heating. Electric-field switching of magnon spin current without charge current is highly preferred but challenging to realize. By integrating magnonic and piezoelectric materials, the manipulation of the magnon spin current generated by the spin Seebeck effect in the ferrimagnetic insulator Gd3Fe5O12 (GdIG) film on a piezoelectric substrate is demonstrated. Reversible electric-field switching of magnon polarization without applied charge current is observed. Through strain-mediated magnetoelectric coupling, the electric field induces the magnetic compensation transition between two magnetic states of the GdIG, resulting in its magnetization reversal and the simultaneous switching of magnon spin current. This work establishes a prototype material platform that paves the way for developing magnon logic devices characterized by all electric field reading and writing and reveals the underlying physics principles of their functions.

Coarse-graining collective skyrmion dynamics in confined geometries

Magnetic skyrmions are magnetic quasi-particles with enhanced stability and different manipulation mechanisms using external fields and currents, making them promising candidates for future applications such as neuromorphic computing. Recently, several measurements and simulations have shown that thermally activated skyrmions in confined geometries, as they are necessary for device applications, arrange themselves predominantly based on commensurability effects. In this simulational study, based on the Thiele model, we investigate the enhanced dynamics and degenerate non-equilibrium steady state of a system in which the intrinsic skyrmion–skyrmion and skyrmion–boundary interaction compete with thermal fluctuations as well as current-induced spin–orbit torques. The investigated system is a triangular-shaped confinement geometry hosting four skyrmions, where we inject spin-polarized currents between two corners of the structure. We coarse grain the skyrmion states in the system to analyze the intricacies of arrangements of the skyrmion ensemble. In the context of neuromorphic computing, such methods address the key challenge of optimizing readout positions in confined geometries and form the basis for understanding collective skyrmion dynamics in systems with competing interactions on different scales. The findings are corroborated by experimental measurements.

Variety of Mechanically Induced Spin Currents in Rashba Systems

Various types of spin currents, including unconventional types, are generated in Rashba spin-orbit coupled systems by dynamic lattice distortions associated with, for example, surface acoustic waves.

Spin–orbit torques and magnetization switching in Gd/Fe multilayers generated by current injection in NiCu alloys

Light transition metals have recently emerged as a sustainable material class for efficient spin–charge interconversion. We report measurements of current-induced spin–orbit torques generated by Ni1−xCux alloys in perpendicularly magnetized ferrimagnetic Gd/Fe multilayers. We show that the spin–orbit torque efficiency of Ni1−xCux increases with the Ni/Cu atomic ratio, reaching values comparable to those of Pt for Ni55Cu45. Furthermore, we demonstrate magnetization switching of a 20-nm-thick Gd/Fe multilayer with a threshold current that decreases with increasing Ni concentration, similar to the spin–orbit torque efficiency. Our findings show that Ni1−xCux−based magnetic heterostructures allow for efficient control of the magnetization by electric currents.

Bilinear magnetoresistance in 2DEG with isotropic cubic Rashba spin–orbit interaction

Bilinear magnetoresistance has been studied theoretically in 2D systems with isotropic cubic form of Rashba spin–orbit interaction. We have derived the effective spin–orbital field due to current-induced spin polarization and discussed its contribution to the unidirectional system response. The analyzed model can be applied to the semiconductor quantum wells as well as 2DEG at the surfaces and interfaces of perovskite oxides.

Current-induced spin accumulation and magnetoresistance in chiral semimetals

Current-induced spin accumulation and magnetoresistance in chiral semimetals

Anomalous Hall effect in naturally oxidized normal-metal Al/Cu double films

An unexpectedly larger current-induced spin–orbit torque in oxidized Cu (CuO x )/ferromagnet (FM) than heavy-metal/FM has recently attracted intense attention in spintronic studies. Although the two mechanisms, interfacial Rashba Edelstein effect and spin-vorticity coupling, have been put forward based on the two different conductive features of CuO x , i.e. electrical insulator and gradient of electrical mobility, the detailed investigation of transport of CuO x is still lacking. Here we experimentally report the positive and negative anomalous Hall effect (AHE) in naturally oxidized normal-metal Al/Cu double films. We found that the onset temperature of AHE corresponds to magnetic transition temperature of CuO x . Furthermore, by comparing Hall resistance of the crystalline and amorphous Cu/Al double films, we identify that the positive anomalous Hall resistance attributes to magnetic moment of CuO x itself, while the negative anomalous Hall resistance can originate from the spin or orbital currents generated at the CuO x /AlO x interface interact with magnetization of CuO x and its inverse process.