Spin-Orbit Torque Switching of Ferromagnets and Antiferromagnets

Spin-orbit torque (SOT), using pure spin current from heavy metals (HMs) to switch ferromagnets (FMs), enables electrical switching in FM/HM bilayers, where the FM magnetization before and after SOT can be unequivocally verified. We discuss schemes that can achieve field-free SOT switching of FM with perpendicular magnetic anisotropy (PMA). Far more challenging is SOT switching of antiferromagnetic (AF) Néel vector, whose existence cannot be readily verified. SOT switching of AF has been claimed in patterned 8- or 4-terminal AF/HM bilayers by applying a high current density. However, similar voltages remain without the AF layer, demonstrating that the signals are unrelated to AF switching but the thermal signals from the HM. SOT switching in synthetic AF consisting of two interlayer-coupled FMs with PMA reveals SOT switching efficiency in a magnetic entity with different net magnetizations and directions.

In collaboration with Q. Ma and Y. Li at Johns Hopkins University, C. Chiang, P. Wu, and S. Huang at National Taiwan University and D. Qu at Academia Sinica.