Annealing temperature dependence of the bulk spin–orbit torque in CoPt film

The recent discovery of bulk spin–orbit torques (SOTs) in magnetic single layers has attracted much recent attention. However, currently, it remains elusive as to how to understand and how to tune such bulk SOTs. In this study, we study the tunability of the bulk SOTs in the CoPt films, by the annealing temperature. Our results show that the field-free switching can be realized after annealing and optimized at 450 °C. The switching performance is consistent with the out-of-plane SOT efficiency, which also appears after annealing and maximized at 450 °C. The crystal-axis dependence of the switching performance reveals that besides the threefold modulation by the crystal-axis, the switching ratio also contains a contribution that is independent of the crystal-axis, which is different from that in single-crystal films. Our results can help the understanding of the mechanism of SOT and point to the developing of SOT devices.