Spin‐Orbit Torque (SOT) Materials and Devices

Although spin-transfer torque (STT) is currently the main way of writing information in commercial magnetic random access memory (MRAM), the writing speed and power consumption are not satisfactory [1–4]. Furthermore, a high current density needs to directly pass through the very thin insulating tunnel barrier in the writing process, which will strongly reduce the endurance of the device. Recently, as an alternative to STT, spin-orbit torque (SOT) has attracted considerable attention due to the advantages of higher speed, lower-power consumption and better endurance [5–8]. The SOT-induced magnetization switching was first discovered in ferromagnetic semiconductor GaMnAs [9, 10]. Because of the coexistence of Rashba and Dresselhaus spin-orbit coupling (SOC) in GaMnAs thin films, an anisotropic current-induced magnetization switching was observed [11, 12]. Soon after, room temperature SOT-induced magnetization switching in multilayer ferromagnetic films was demonstrated by Miron et al. [13, 14] and Liu et al. [15], which has been widely regarded as the core technology of next-generation MRAM. In this chapter, we introduce the underlying physics of SOT-induced switching. Then, we review the recent progress of SOT in materials and devices. Finally, we will look towards the challenges and opportunities for future development of the related materials and devices.