Spin–orbit torques in ferrimagnetic Gd/FeCo multilayers

Abstract

The Gd thickness dependence of spin–orbit torque (SOT) and critical current density of SOT switching in ferrimagnetic Gd/FeCo multilayers grown on a Ta seed layer was investigated and compared with the results on GdFeCo alloy/Ta bilayers. Critical current density of SOT switching J sw of Gd/FeCo multilayers was almost the same as those of the GdFeCo alloy films. The magnitudes of damping-like and field-like SOT effective fields, H DL and H FL, respectively, in Gd/FeCo multilayers were confirmed to increase near the compensation point, and the sign of H FL in Gd/FeCo multilayers was confirmed to change across the compensation point as well as GdFeCo alloy. Damping-like and field-like SOTs, estimated by multiplying the SOT effective fields by net magnetization, exhibited slightly smaller values for TM-dominant Gd/FeCo than for TM-dominant GdFeCo, while RE-dominant Gd/FeCo shows almost the same SOTs as RE-dominant GdFeCo.