Efficient Tuning of the Spin-Orbit Torque via the Magnetic Phase Transition of FeRh.

The understanding and control of the spin-orbit torque (SOT) are central to antiferromagnetic spintronics. Despite the fact that a giant SOT efficiency has been achieved in numerous materials, its efficient tuning in a given material has not been established. Materials with magnetic phase transitions (MPTs) offer a new perspective, as the SOT efficiency may vary significantly for the different magnetic orderings across the transition, and the transition itself can be readily tuned by various control parameters. This work reports that the SOT efficiency of a FeRh-based perpendicular magnetized heterostructure can be significantly tuned by varying the temperature across the MPT. The SOT efficiency exhibits a temperature hysteresis associated with the first-order nature of the MPT, and its value in the ferromagnetic phase is seen to be enhanced by ∼450%, simply by a lowering of temperature to drive FeRh into the antiferromagnetic phase. Furthermore, current-induced magnetization switching can be achieved without an assistant magnetic field for both ferromagnetic and antiferromagnetic FeRh, with a low critical switching current density for the latter. These results not only directly establish FeRh as an efficient spin generator but also present a strategy to dynamically tune SOT via varying the temperature across MPTs.