Sign reversal of current-induced torque in perpendicularly magnetized Pd/Co2MnGa and Pd/Co2MnSi

We studied the effective magnetic field Heff arising from the spin–orbit torque (SOT) and/or orbital torque (OT) by measuring shifts of out-of-plane hysteresis loops under various in-plane currents Is and in-plane magnetic fields Hxs along I in perpendicularly magnetized Pd/Co2MnGa (CMG) and Pd/Co2MnSi (CMS). The Heff for Pd/CMS is explained well by the SOT originating from the spin Hall effect (SHE) in Pd, whereas that for Pd/CMG points in the opposite direction under a given polarity of I and Hx. Neither the self-induced SOT in CMG nor the SOT originating from the interfaces is responsible for the Heff reversing in Pd/CMG. The magnitude of the effective spin/orbital Hall angle, derived from the Heff, increases with the thickness of both the CMG and Pd layers in Pd/CMG, which is consistent with the predicted behavior of the OT originating from the orbital Hall effect in Pd. Considering these results and the fact that CMG has stronger spin–orbit interaction than CMS, the OT, which is larger than and opposite to the SOT originating from the SHE in Pd, is a plausible candidate for reversing the Heff in Pd/CMG.