Interplay of Spin Current and Magnetization in a Topological-insulator/Magnetic-insulator Bilayer Structure

The interaction between accumulated spins on the surface of a heavy metal and the magnetization of an adjacent magnet material leads to various spin phenomena, such as spin orbit torque, spin pumping, and spin Hall magnetoresistance (SHMR). However, the exploration of device applications based on these spin phenomena is often limited by the low charge-to-spin conversion efficiency of the heavy metal. Recent studies have suggested that topological insulators are promising candidates for device applications due to their potentially higher charge-to-spin conversion efficiency. In this work, we systematically studied the interplay of spin current and magnetization in a bilayer structure consisting of Bi₂Se₃ and YIG. Our ferromagnetic resonance measurements demonstrate that microwave excitation can efficiently pump spins from YIG to Bi₂Se₃. The transfer of spin current from YIG to Bi₂Se₃ is further confirmed by detection of an electromotive force generated in Bi₂Se₃ via spin-to-charge conversion. Moreover, angle dependent magneto-transport measurements suggest that despite the large out-of-plane magnetoresistance of Bi₂Se₃ itself, the interfacial spin diffusion from the magnetic insulator to the topological insulator can effectively affect the longitudinal transport in a way similar to the SHMR effect.