The dominancy of damping like torque for the current induced magnetization switching in Pt/Co/W multilayers

Two classes of spin-orbit coupling (SOC) mechanisms have been considered as candidate sources for the spin orbit torque (SOT): the spin Hall Effect (SHE) in heavy metals with strong SOC and the Rashba effect arising from broken inversion symmetry at material surfaces and interfaces. In this work, we have investigated the SOT in perpendicularly magnetized Pt/Co/W films, which is compared with the results in Pt/Co/AlOx films. Using the harmonic measurements, we have characterized the effective fields corresponding to the damping like torque and the field like torque. Theoretically, in the case of the asymmetrical Pt/Co/W trilayers with opposite sign of spin Hall angle, both damping like torque and field like torque due to the SHE and the Rashba effect will be enhanced, but we have found the dominancy of damping like torque in the Pt/Co/W films. It is much different from the results in the Pt/Co/AlOx films, in which both the damping like torque and the field like torque are evident.