Room Temperature Highly Efficient Topological Insulator/Mo/CoFeB Spin-Orbit Torque Memory with Perpendicular Magnetic Anisotropy

Spin-orbit torque (SOT)-MRAM is a promising candidate for future nonvolatile memory technology. Finding materials that have large SOT efficiency $(\xi_{\text{DL}})$ is critical for developing the SOT-MRAM. Topological insulators (TIs) have been shown to exhibit giant $\xi_{\text{DL}}$ (>1) at room temperature. However, integration of high $\xi_{\text{DL}}$ TIs with CoFeB with perpendicular magnetic anisotropy (PMA) at room temperature (RT) has not been achieved. In this work, we demonstrate a record-high $\xi_{\text{DL}}$ (∼2.66) in the (BiSb)2Te3 with PMA CoFeB and achieve magnetization switching with TI current density as low as $3\times 10^{9}\mathrm{A}/\mathrm{m}^{2}$ at RT. For the first time, we propose to insert a light metal spacer between TI and CoFeB to achieve resistance matching and thus reduce write energy. We show that without insertion, TI/CoFeB show in-plane magnetic anisotropy but TIs show high $\xi_{\text{DL}}$, consistent with previous reports. We then insert a Mo spacer to achieve PMA at RT. We accurately determine the $\xi_{\text{DL}}$ using both second harmonic method and MOKE for the first time. We investigate the SOT-driven switching and discover a memristor-like behavior in the TI/Mo/CoFeB.