Switching of Perpendicular Magnetization by Spin–Orbit Torque

Abstract

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.

Asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction

“…1c ) that promotes or hinders the switching of perpendicular magnetization, ultimately leading to a number of striking consequences, e.g., strong asymmetry in the switching density, hysteresis loop shift in the absence of in-plane direct current, and switching of perpendicular magnetization purely by an in-plane magnetic field. None of these characteristics can be attributed to the short-range interfacial DMI 6 , 9 , 11 . We also demonstrate that the long-range intralayer DMI effect provides a new platform for designing functional spintronic devices.…”

“…Despite the enormous investigations in the past two decades 1 – 8 , the understanding of in-plane current-induced switching of perpendicular magnetization remains elusive as indicated by a number of remarkable long-standing puzzles (see ref. 9 for a review of this problem). In many spin-orbit torque (SOT) heterostructures, such as heavy metal/ferromagnet (HM/FM) bilayers with perpendicular magnetic anisotropy (PMA), the scaling of the switching current density with the SOT and the applied magnetic field is in strong disagreement with the predictions of the existing macrospin and chiral-domain-wall depinning models 10 , 11 .…”

“…The in-plane magnetic field hinders rather than assists current-driven switching of perpendicular magnetization in some cases 17 . Quantitatively, analyses of the switching current density following the macrospin and chiral-domain-wall depinning models 10 , 11 typically overestimate or underestimate the SOT efficiency of a PMA heterostructure by up to thousands of times 9 , 18 , 19 . These remarkable puzzles suggest that some fundamental physics for electrical switching of magnetization is yet to be discovered.…”

Recent advances in two-dimensional intrinsic ferromagnetic materials Fe3X(X=Ge and Ga)Te2 and their heterostructures for spintronics

“…Spin transparency ( T int ) is expected to be large, 35 which is related to ξ by the equation ξ = θ SH ·T int . The mechanism of SOT, along with the details of damping-like, field-like, and anti-damping torques affecting the magnetization of the FM layer, has been extensively reviewed 156–159 and is not described herein. This study mainly focuses on the SOT effect based on 2D Fe 3 X ( X =Ge and Ga)Te 2 .…”

Giant, Linearly Increasing Spin–Orbit Torque Efficiency in Symmetry-Broken Spin–Orbit Torque Superlattices

“…Spin–orbit torques (SOTs) provide an effective knob for electrically manipulating magnetization for low-power nonvolatile magnetic memory and computing. − Because the power of a SOT device is, in general, inversely proportional to the square of the efficiency of the dampinglike SOT ( ξ D L j ), the development of a high- ξ D L j SOT material scheme has become a core topic in the field of spintronics. In the most commonly studied spin Hall metal/magnet bilayer, the ξ D L j exerted on the magnetic layer by the spin current generated by the spin Hall metal is generally given by ξ D L j = T i n t θ S H τ M − 1 / false( τ normalM − 1 + τ normals normalo − 1 false) where T int is the spin transparency of the interface, − θ SH is the spin Hall ratio of the spin-current generator, τ M –1 is the spin relaxation rate due to spin-magnetization exchange interaction, and τ so –1 is t...…”