Enhanced spin-orbit torque by engineering Pt resistivity in Pt/Co/AlOx structures

The magnetization direction in heavy-metal (HM)/ferromagnet bilayers can be electrically controlled by spin-orbit torque (SOT); however, the efficiency of the SOT which depends on the spin-orbit coupling of the HM layer or its spin-Hall angle has to be improved further for actual applications. In this study, we report a significant enhancement of the spin-Hall effect of Pt and resultant SOT in Pt/Co/AlOx structures by controlling the Pt resistivity. We observed that the effective spin-Hall angle increases about three times as the resistivity of Pt layer is increased 1.6 times by changing the Ar deposition pressure from 3 to 50 mTorr. This enhancement in effective spin-Hall angle is confirmed by the reduction in the critical current for SOT-induced magnetization switching. Furthermore, x-ray absorption spectroscopy analysis reveals a non-negligible contribution of the interfacial spin-orbit coupling to the effective spin-Hall angle. Our result, the efficient control of effective spin Hall angle by controlling the HM resistivity, paves the way to improved switching efficiency in SOT-active devices.