Investigation of Spin Pumping in Fe$_{3}$Si/GaAs and Fe$_{3}$Si/Bi$_{2}$Se$_{3}$ Bilayer Structure

Spin pumping, a dynamical spin-injection method to generate a pure spin current by magnetization precession, can be used to conduct the spin injection into a wide range of materials. Here we report the spin pumping experiment by utilizing epitaxial ferromagnetic Fe$_{3}$Si thin films interfaced with GaAs for spin injection into semiconductor, and interfaced with Bi$_{2}$Se$_{3}$ for exploitation of topological insulator (TI) edge or surface states at the TI/ferromagnet (FM) interfaces. An inverse spin Hall effect voltage as large as 49 $\mu$V, and 19 $\mu$V was detected in Fe$_{3}$Si/p-GaAs, and Fe$_{3}$Si/n-GaAs structures, respectively, under a microwave power of 100 mW. Our analysis showed that the spin injection efficiency is affected by the Schottky barrier height of Fe$_{3}$Si/(n- or p-) GaAs interface, and so is the spin mixing conductance. As for the TI/FM structure, an out of plane spin transfer torque is generated due to current driven spin accumulations. Spin pumping in Fe$_{3}$Si/Bi$_{2}$Se$_{3}$ structure using Pt electrodes has been carried out to elucidate spins diffusion process from Fe$_{3}$Si via Bi$_{2}$Se$_{3}$ into Pt, and will be reported.