Enhanced current-induced torque efficiency in Pt/Co/Tb/Cr structures through the synergistic action of orbital torque effect

We investigated the impact on the spin–orbit torque (SOT) efficiency by varying the thickness of the Cr and Tb layers in the Pt/Co/Tb/Cr system. The harmonic Hall voltage measurement shows that the Tb insert layer effectively enhances the damping-like (DL) torque efficiency, which is ascribed to the conversion of the orbital current to spin current in the Tb layer. Additionally, by fitting the Cr thickness dependence of the measured DL torque efficiency with an orbital current diffusion model, we obtained the orbital diffusion length of the Cr layer of 5.3 ± 0.3 nm and the effective orbital Hall angle of −0.18 ± 0.01. Furthermore, current-induced magnetization switching measurement suggested that the critical switching current density decreases with the insertion of the Tb layer and the increasing Cr layer thickness. Our findings offer valuable insights into the improvement of SOT efficiency by utilizing the orbital current effect and open avenues for developing energy-efficient spintronics devices.