Large enhancement of effective spin-orbit torque efficiency by optimizing the capping layer thickness in Ta/Pt/Co trilayer.

We report the influence of the capping layer thickness on the effective magnetic damping and the effective spin-orbit torque (SOT) efficiency in Ta/Pt/Co structures via spin-torque ferromagnetic resonance measurements. The SOT efficiency first increases with increasing capping layer thickness (dTa), reaching a large value of 0.199 at dTa= 1.4 nm, then decreases with further increases indTa. This can be attributed to a competition between the additional SOT field generated by the Rashba-Edelstein effect and the reduced net spin current effect. It has been demonstrated that the magnetic damping factor decreases with increasing capping layer thickness. The high SOT efficiency and low magnetic damping factor suggest the great potential of the Ta/Pt/Co for low-power spintronic technologies.