Enhanced Spin-Orbit Torque and Multilevel Current-Induced Switching in W/Co-Tb/Pt Heterostructure

Spin-orbit torque (SOT) driven magnetization switching in ferrimagnets (FIMs) can inspire a variety of low-power, high-speed, and multifunctional spintronic devices. SOT efficiency in ferrimagnet/heavy-metal (FIM/HM) systems has recently been found to be increased when the FIM is approaching its magnetic compensation point. However, the effective spin Hall angle cannot be obviously augmented due to the magnetization reduction. We investigate an enhanced SOT effect in a heterostructure composed of a near-compensated Co-Tb layer sandwiched by W and Pt layers, where Co-Tb is a rare-earth-transition-metal ferrimagnetic alloy with bulk perpendicular magnetic anisotropy and W has the opposite spin Hall angle to Pt. Beyond a large SOT efficiency, a 1.9 times more effective spin Hall angle and 20% switching power consumption can be achieved by optimizing the thickness of the HM layers compared to SOT-driven magnetization switching in a conventional FIM/HM structure. Moreover, based on this heterostructure, four-state current-induced magnetization switching is carried out. This work provides an alternative way to enhance the SOT effect in FIM/HM systems and promotes the use of FIMs for future high-performance memory and computation.