Spin-orbit torque study on MBE-grown Bi_1-xSb_x thin films

Strong spin-orbit torque (SOT) generated by the surface and bulk states in topological insulator (TI)/ferromagnet heterostructures offers new opportunities in thin film magnetization manipulation for low power-consumption magnetoresistive random-access memory devices. The Bi_1-xSb_x alloy system has recently attracted interest in this context because of energy-efficient SOT switching [Nature Mater. 17, 808 (2018)]. This motivated us to study current-induced SOT in thin film Bi_1-xSb_x/ferromagnet heterostructures via spin-torque ferromagnetic resonance (ST-FMR). We briefly describe the synthesis by molecular beam epitaxy of Bi_1-xSb_x thin films and their characterization via reflection high energy diffraction, x-ray diffraction, transmission electron spectroscopy, and in vacuo angle-resolved photoemission spectroscopy. We then discuss the ST-FMR measurement of SOT at room temperature in Bi_1-xSb_x thin films as we vary the composition within and outside the topological regime.