Spin-orbit torques and magnetotransport properties of α-Sn and β-Sn heterostructures

Topological insulators have emerged as an important material class for efficient spin-charge interconversion. Most topological insulators considered to date are binary or ternary compounds, with the exception of alpha-Sn. Here we report a comprehensive characterization of the growth, magnetotransport properties, and current-induced spin-orbit torques of alpha-Sn and beta-Sn-based ferromagnetic heterostructures. We show that alpha-Sn grown with a Bi surfactant on CdTe(001) promotes large spin-orbit torques in a ferromagnetic FeCo layer at room temperature, comparable to Pt, whereas alpha-Sn grown without Bi surfactant and the nontopological phase, beta-Sn, induce lower torques. The dampinglike and fieldlike spin-orbit torque efficiency in alpha-Sn with Bi are 0.12 and 0.18, respectively. Further, we show that alpha-Sn grown with and without Bi presents a spin-Hall-like magnetoresistance comparable to that found in heavy metal/ferromagnet bilayers. Our work demonstrates direct and efficient charge-to-spin conversion in alpha-Sn ferromagnetic heterostructures, showing that alpha-Sn is a promising material for current-induced magnetization control in spintronic devices.