Current‐Induced Spin–Orbit Torques for Spintronic Applications

Abstract

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 its efficient manipulation of the magnetization using in‐plane current. SOT spearheads novel spintronic applications including high‐speed magnetic memories, reconfigurable logics, and neuromorphic computing. Herein, recent advances in SOT research, highlighting the considerable benefits and challenges of SOT‐based spintronic devices, are reviewed. First, the materials and structural engineering that enhances SOT efficiency are discussed. Then major experimental results for field‐free SOT switching of perpendicular magnetization are summarized, which includes the introduction of an internal effective magnetic field and the generation of a distinct spin current with out‐of‐plane spin polarization. Finally, advanced SOT functionalities are presented, focusing on the demonstration of reconfigurable and complementary operation in spin logic devices.

Electrical manipulation of antiferromagnetic easy axis in IrMn/NiFe exchange-biased structures

“…The second is to use AFM/heavy metal bilayers, in which the AFM moment is controlled by the spin current generated by the spin Hall effect 19 in the heavy metal layer and the Rashba-Edelstein effect 20,21 at the interfaces. This is similar to intensively investigated SOT in ferromagnet/heavy metal bilayers [22][23][24][25] .…”

Enhanced Spin Hall Effect in S‐Implanted Pt

“…[ 1–4 ] In heavy metal/ferromagnet (HM/FM) bilayer, upon charge current injection, SHE‐induced spin‐dependent accumulation at the interface leads to generation of transverse spin current ( J s ) that exerts spin–orbit torque (SOT) in FM layer enabling useful applications of magnetization switching, sustained oscillations, excitation of spin‐waves, and fast domain wall motion. [ 4–6 ] The spin current is given as , where θ SH is spin Hall angle that quantifies the charge–spin interconversion efficiency and σ is the spin polarization. Continuous efforts have been made to find suitable HM exhibiting high θ SH , [ 7 ] but to reduce the energy consumption further, for the development of SOT‐based spintronic devices, innovative ways of maximizing θ SH with improved spin Hall conductivity (σ SH ) are on high demand.…”

“…Controlled manipulation of magnetization using spin Hall effect (SHE) has recently brought substantial interest driven by the quest of fundamental physics involved to further meet technological advancements in the emerging field of magnetic memory and logics. [1][2][3][4] In heavy metal/ferromagnet (HM/FM) bilayer, upon charge current (J c ) injection, SHE-induced spin-dependent accumulation at the interface leads to generation of transverse spin current (J s ) that exerts spin-orbit torque (SOT) in FM layer enabling useful applications of magnetization switching, sustained oscillations, excitation of spin-waves, and fast domain wall motion. [4][5][6] The spin current is given as J s = ℏ 2e SH (J c × ), where SH is spin Hall angle that quantifies the chargespin interconversion efficiency and is the spin polarization.…”

Picosecond switching in a ferromagnet

“…A range of SOT-operated devices has been explored for application in memory and logic technologies, including magnetic random-access memory (MRAM) 5 . An MRAM device can store data in the magnetization of the free layer of a magnetic tunnel junction, which can be switched by SOTs 6 (Fig.…”