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R&D: Field-Free Spin–Orbit Torque (SOT) Magnetization Switching in Perpendicularly Magnetized Semiconductor (Ga,Mn) As Single Layer

Findings help to deeply elucidate SOT switching mechanism and can advance development of highly efficient MRAM with better scalability.

ACS Applied Materials & Interfaces has published an article written by Miao Jiang, School of Materials Science and Engineering, Beijing Institute of Technology, Haidian, Beijing 100081, P. R. China, and National Key Laboratory of Science and Technology on Materials under Shock and Impact, Beijing Institute of Technology, Haidian, Beijing 100081, P. R. China, Xinyuan Yang, Department of Electrical Engineering and Information Systems, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan, Shengyuan Qu, School of Materials Science and Engineering, Beijing Institute of Technology, Haidian, Beijing 100081, P. R. China, Chenda Wang, Department of Electrical Engineering and Information Systems, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan, Shinobu Ohya, and Masaaki Tanaka, Department of Electrical Engineering and Information Systems, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan, Center for Spintronics Research Network (CSRN), Graduate School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan, and Institute for Nano Quantum Information Electronics, The University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan.

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 in-plane 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.

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