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 $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$. Here we report a comprehensive characterization of the growth, magnetotransport properties, and current-induced spin-orbit torques of $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$ and $\\ensuremath{\\beta}\\ensuremath{-}\\mathrm{Sn}$-based ferromagnetic heterostructures. We show that $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$ 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 $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$ grown without Bi surfactant and the nontopological phase, $\\ensuremath{\\beta}\\ensuremath{-}\\mathrm{Sn}$, induce lower torques. The dampinglike and fieldlike spin-orbit torque efficiency in $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$ with Bi are 0.12 and 0.18, respectively. Further, we show that $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$ 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 $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$ ferromagnetic heterostructures, showing that $\\ensuremath{\\alpha}\\ensuremath{-}\\mathrm{Sn}$ is a promising material for current-induced magnetization control in spintronic devices.