Spin-orbit torque (SOT) arising from spin-orbit coupling has gained much attention because it promises efficient magnetization switching in spintronic devices . It is important for device applications that the SOT switches perpendicular magnetizations without an external magnetic field. In addition to field-free switching, reducing SOT switching current density is another essential requirement for low energy consumption.
In this talk, I will discuss two approaches to reducing field-free SOT switching current; first, we demonstrate that all three spin polarizations are exploited in a magnetic trilayer comprising an epitaxial bottom ferromagnet with a tilted magnetic easy-axis, and thereby reduces the field-free SOT switching current [2,3]. Second, we show that the lateral modulation of the Rashba effect in Pt/Co/AlOx structures by using a side gate generates out-of-plane SOT, allowing electrical control of field-free switching of perpendicular magnetization [4,5]. Furthermore, it is found that the field-free switching current density gradually reduces when increasing the gate voltage.
 J. Ryu, S. Lee, K.-J. Lee, and B.-G. Park, Adv. Mater. 32, 1907148 (2020)
 S.-h.C. Baek, et al, Nat. Mater. 17, 509 (2018)
 J. Ryu, et al, unpublished manuscript
 S.-h.C. Baek, et al, Nat. Electron. 1, 398 (2018)
 M.-G. Kang, et al, unpublished, preprint at DOI: 10.21203/rs.3.rs-87924/v1