Field-Free Spin–Orbit Torque Magnetization Switching in a Perpendicularly Magnetized Semiconductor (Ga,Mn)As Single Layer

Abstract

Current-induced spin−orbit torque (SOT) in a perpendicularly magnetized single layer has a strong potential to switch the magnetization using an extremely low current density, which is generally 2−3 orders of magnitude smaller than that required for conventional metal bilayer systems. However, an inplane external magnetic field has to be applied to break the symmetry and achieve deterministic switching. To further enhance the high-density integration and accelerate the practical application of highly efficient SOT magnetic random-access memory (SOT-MRAM) devices, field-free SOT magnetization switching in a ferromagnetic single layer is strongly needed. In a spin−orbit ferromagnet (a ferromagnet with strong spin−orbit interaction) with crystal inversion asymmetry and a multi-domain structure, the internal Dzyaloshinskii−Moriya effective fields are considered to induce field-free switching. Here, combined with strong spin−orbit coupling and a tilted anisotropy axis induced by a nonuniform Mn distribution and a possible magnetocrystalline anisotropy resulting from a slight substrate tilting, we successfully achieve magnetization switching in a spin−orbit ferromagnet (Ga,Mn)As single layer by utilizing SOT without applying any external magnetic field. Our findings help to deeply elucidate the SOT switching mechanism and can advance the development of a highly efficient MRAM with better scalability.