Field-Free\nSpin–Orbit Torque Magnetization\nSwitching in a Perpendicularly Magnetized Semiconductor (Ga,Mn)As\nSingle Layer

Abstract

Current-induced\nspin–orbit torque (SOT) in a perpendicularly\nmagnetized single layer has a strong potential to switch the magnetization\nusing an extremely low current density, which is generally 2–3\norders of magnitude smaller than that required for conventional metal\nbilayer systems. However, an in-plane external magnetic field has\nto be applied to break the symmetry and achieve deterministic switching.\nTo further enhance the high-density integration and accelerate the\npractical application of highly efficient SOT magnetic random-access\nmemory (SOT-MRAM) devices, field-free SOT magnetization switching\nin a ferromagnetic single layer is strongly needed. In a spin–orbit\nferromagnet (a ferromagnet with strong spin–orbit interaction)\nwith crystal inversion asymmetry and a multi-domain structure, the\ninternal Dzyaloshinskii–Moriya effective fields are considered\nto induce field-free switching. Here, combined with strong spin–orbit\ncoupling and a tilted anisotropy axis induced by a nonuniform Mn distribution\nand a possible magnetocrystalline anisotropy resulting from a slight\nsubstrate tilting, we successfully achieve magnetization switching\nin a spin–orbit ferromagnet (Ga,Mn)As single layer by utilizing\nSOT without applying any external magnetic field. Our findings help\nto deeply elucidate the SOT switching mechanism and can advance the\ndevelopment of a highly efficient MRAM with better scalability.