Enhancement of spin-orbit torque by inserting CoOx layer into Co/Pt interface

We report that the spin-orbit torque (SOT) in a Co/Pt structure is significantly enhanced by partial oxidation of the Co-side interface. The interface-oxidized and unoxidized Co/Pt samples were prepared to compare the SOTs, which were determined using the harmonic Hall measurement. Even though an insulating ${\mathrm{CoO}}_{x}$ layer exists at the Co/Pt interface, the dampinglike and fieldlike SOT efficiencies in the interface-oxidized sample were severalfold and nearly an order of magnitude larger than those of the unoxidized sample, respectively. The enhancement of the SOT is most likely attributed to the efficient spin current transmission across the ${\mathrm{CoO}}_{x}$ layer and the appropriately modulated interfacial Rashba effect.