Layer thickness dependence of spin orbit torques and fields in Pt/Co/AlO trilayer structures

We investigated the strength of the spin orbit interaction induced effective magnetic fields originating from two distinct mechanisms of different symmetry in Pt/Co/AlO trilayer films with varying Pt and Co thicknesses. Films are deposited by RF magnetron sputtering and effective magnetic fields are measured using an AC current induced magnetization oscillation technique. Based on the Pt thickness dependence, a transverse effective field perpendicular to both magnetization and current directions resembled Rashba effect while a longitudinal field parallel to the current direction was resembled to the spin Hall effect. More overwhelming is the sensitivity of the transverse and longitudinal fields to the Co layer which drastically increased when the Co thickness was changed from 0.6 to 0.9 nm. The sensitivity of the layer thickness indicates the importance of relative current distribution of the current density per layer in achieving a consensus of the widely controversial spin orbit strength in Pt/Co/AlO and other similar films.