Spin-orbit torques: Materials, mechanisms, performances, and potential applications

Current-induced spin-orbit torque (SOT) is attracting increasing interest and exciting significant research activity. We aim to provide a comprehensive review of recent progress in SOT in various materials. The intrinsic correlation between the heterostructure and SOT behaviors is emphasized. We first present a brief summary of the spin-orbit coupling in inversion-asymmetric magnetic systems and describe the discovery, classification and development of SOT. Then we focus on the characterization techniques and classification of SOT from the viewpoint of materials, including both spin sources and magnetic functional layers. In the third part, the mechanisms of SOT are discussed in detail, including spin Hall effect, Rashba effect, and emerging new mechanisms. The fourth part illustrates SOT in subdivided magnetic systems, including heavy metal combined with ferromagnets, ferrimagnets and antiferromagnets, and systems with topological insulators and single layer magnets. The fifth part presents typical performances of SOT, including the modulation, improvement, and field-free switching through material design, and discusses its promising applications for non-volatile SOT-magnetic random access memory and other device configurations. We conclude with a discussion of the challenges and future prospects of SOT, which will inspire more in-depth research and advance the practical applications.