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 (HM) and the magnetization of an adjacent magnetic 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 HM. Authors of recent studies have suggested that topological insulators (TIs) are promising candidates for device applications due to their potentially higher charge-to-spin conversion efficiency. Here, we report a multifaceted study of a bilayer structure consisting of Bi2Se3 and Y3Fe5O (YIG) and demonstrate an approach based on angle-dependent magnetoresistance (ADMR) measurements to determine the effective charge-to-spin conversion efficiency in TIs. Our ferromagnetic resonance measurements demonstrate efficient spin pumping from YIG to Bi2Se3, which is further confirmed by detection of an electromotive force generated in Bi2Se3 via spin-to-charge conversion. Our ADMR measurements show that the interfacial spin diffusion can significantly affect the charge transport in a way like the SHMR effect and provide an estimate of the charge-to-spin conversion efficiency in Bi2Se3 of similar to 0.1-0.4. Neglecting to account for the large out-of-plane magnetoresistance of the Bi2Se3 results in a fivefold overestimate of the charge-to-spin conversion efficiency.