Enhanced spin-orbit torque in Pt/Co/Pt multilayers with inserting Ru layers

We report the enhancement of spin-orbit torque (SOT) in Pt/Co/Pt multilayers with inserting Ru layers. From current induced magnetization switching and harmonic measurements, we have found that both the damping-like and field-like effective fields increased with inserting Ru layers. The variation is firstly ascribed to the enhancement of the effective spin accumulation at the Co/Ru interfaces. Meanwhile, the interfacial Rashba effect has also been modulated, which depends on the direction of the internal electric field gradient at the interfaces. Our study provides an alternative way to modulate SOT.