Optical Detection of Spin Dynamics in WTe₂/α-Fe₂O₃ bilayers generated by current-induced SOT

Nitrogen-vacancy (NV) centers in diamond enable non-invasive optical detection of magnetization dynamics of spin systems. NV centers can be hyper-polarized and read-out optically at room temperature to enable sensitive measurements of magnetic fields at the nanoscale. In particular, the dynamics in ferromagnetic (FM) and antiferromagnetic (AFM) materials produce local field fluctuations that can be detected by the NV centers. The switching of antiferromagnetic materials (AFM) has attracted attention for the numerous benefits that they can offer to novel spintronic applications. In α-Fe₂O_3, spin dynamics can be excited by electrical current pulses through heavy metal/α-Fe₂O₃ devices that switch the Neel vector between two easy axes. Any perturbation or dynamics of the Néel vector produces magnons that can be detected by the NV center. In general, the dynamics of the Néel vector can be achieved by spin-orbit torque (SOT), however, efficient control and manipulation of AFM magnetization is challenging. Recently, transition-metal dichalcogenides with low-symmetry crystal structure, such as WTe₂, have been shown to exhibit an out-of-plane SOT when a DC current flows along its low-symmetry axis. To this end, we employ NV centers to optically detect Néel vector dynamics in α-Fe₂O₃ driven by the out-of-plane SOT in WTe₂.