A conductive topological insulator with colossal spin Hall effect for ultra-low power spin-orbit-torque switching

Abstract

Spin-orbit-torque (SOT) switching using the spin Hall effect (SHE) in heavy metals and topological insulators (TIs) has great potential for ultra-low power magnetoresistive random-access memory (MRAM). To be competitive with conventional spin-transfer-torque (STT) switching, a pure spin current source with large spin Hall angle (${\theta }_{SH}$ > 1) and high electrical conductivity ($\sigma >10^5{\Omega }^{-1}{m}^{-1}$) is required. Here, we demonstrate such a pure spin current source: BiSb thin films with $\sigma \sim 2.5\ast 10^5{\Omega }^{-1}{m}^{-1}$, ${\theta }_{SH}\sim 52$, and spin Hall conductivity ${\sigma }_{SH}\sim 1.3\ast 10^7\hslash /2e{\Omega }^{-1}{m}^{-1}$ at room temperature. We show that BiSb thin films can generate a colossal spin-orbit field of 2770 Oe/(MA/cm${}^2$) and a critical switching current density as low as 1.5 MA/cm${}^2$ in Bi${}_{0.9}$Sb${}_{0.1}$ / MnGa bi-layers. BiSb is the best candidate for the first industrial application of topological insulators.