Narrow Results

Spin–orbit torque provides an efficient way to switch magnets for low power memory applications by reducing the current density needed to switch the magnetization. Perpendicularly polarized magnets are preferred for high density data storage applications because of their high thermal stability in scaled dimensions. However, spin–orbit torque cannot switch a perpendicularly polarized magnet deterministically from up to down and down to up in the absence of an external magnetic field because spin–orbit torque alone cannot break the symmetry of the system. This poses a severe challenge to the applicability of spin–orbit torque for memory devices. In this paper, we show through micromagnetic simulations that when spin–orbit torque is applied on a magnet with a wedge shape, the moments of the magnet are aligned in-plane. On removal of the spin–orbit torque the moments deterministically evolve to vertically upward or downward direction because the anisotropy axis of the magnet is tilted away from the vertical direction owing to the wedge shape of the magnet. Thus, spin–orbit torque driven deterministic switching of the magnet in the absence of an external magnetic field is possible.

In this paper, we investigate theoretically the spin–orbit torque (SOT) as well as the Gilbert damping for a two band model of a 2D helical surface state with a ferromagnetic (FM) exchange coupling. We decompose the density matrix into the Fermi sea and Fermi surface components and obtain their contributions to the electronic transport as well as the SOT. Furthermore, we obtain the expression for the Gilbert damping due to the surface state of a 3D topological insulator (TI) and predict its dependence on the direction of the magnetization precession axis.

Two decades after the discovery of the giant magnetoresistance that revolutionizes the hard disk drive, the rapid development of spin torque-based magnetic random access memory has once again demonstrated the great potential of spintronics in practical applications. While the industrial application is mainly focusing on the implementation of current-induced spin transfer torque (STT) in magnetic tunnel junctions, a new type of spin torque emerges due to the spin–orbit interaction in magnetic multilayers. A great effort has been devoted by the scientific community to study the so-called spin–orbit torque (SOT), which is not only of interest to fundamental science, but also exhibits potential for the application of current-induced magnetization switching. In this paper, we will review recent development in the SOTs including the fundamental understanding, materials development and measurement techniques. We will also discuss the challenges of using the SOT in potential applications, particularly on the switching of perpendicularly magnetized films.

In the recent past, exploiting nonvolatile memory devices to facilitate in-memory computation benchmarks has demonstrated a considerable capability to address the von-Neumann drawbacks. This process resulted in a tremendous effort towards spintronics memory development. Due to the voltage-controlled magnetic anisotropy (VCMA) effect, the toggle magnetoresistive random-access memory (MRAM) exhibits faster switching and lower power consumption than spin-transfer torque (STT) MRAM. We assessed read/write access time, magnetized time and anisotropic field for crystalline perpendicular magnetic tunnel junctions (CPMTJ) with detailed material study and device parameters in this work. These junctions are affected by the VCMA effect. Various VCMA parameters, including the VCMA coefficient, the time constant and antiparallel (AP) resistance on the saturated magnetization, are measured via the memory cell’s SPICE modeling. The Rashba spin–orbit interaction (SOI) and spin-valve model are developed by MATLAB scripting for evaluating a Rashba and Hamiltonian vector field. The toggle spin torque (TST) in the TST-MRAM cell is generated due to the interconnection between STT and spin–orbit torque (SOT) mechanisms. The TST-MRAM cell’s benefits are energy efficiency, large TMR ratio and superfast read and write operation. This work’s novel part is that the Hamiltonian field can control the net magnetization factor by the Rashba SOI effect. We end this paper with the performance enhancement techniques of MRAM cells due to VCMA and Rashba SOI effect.

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.