Deterministic Switching of a Perpendicularly Polarized Magnet Using Unconventional Spin-Orbit Torques in WTe2

Abstract

Abstract Body: Spin-orbit torque (SOT) driven deterministic control of the magnetization state of a magnet with perpendicular magnetic anisotropy (PMA) is key to next-generation spintronic applications including non-volatile, ultrafast, and energy-efficient data storage devices1-3. But field-free deterministic switching of perpendicular magnetization remains a challenge because it requires an out-of-plane anti-damping torque, which is not allowed in conventional spin source materials such as heavy metals (HM)1-3 and topological insulators4 due to system symmetry. The exploitation of low-crystal symmetries in emergent quantum materials offers a unique approach to achieve spin-orbit torque with unconventional form5,6. Here, we report the first experimental realization of field-free deterministic magnetic switching of a perpendicularly polarized van der Waals (vdW) magnet employing an out-of-plane anti-damping SOT generated in layered WTe2 which is a low-crystal symmetry quantum material. The numerical simulations confirm that out-of-plane antidamping torque in WTe2 is responsible for the observed magnetization switching in the perpendicular direction. 1. Miron, I. M. et al. Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. Nature 476, 189-193, (2011). 2. Liu, L. et al. Spin-Torque Switching with the Giant Spin Hall Effect of Tantalum. Science 336, 555-558, (2012). 3. Liu, L. et al. Current-Induced Switching of Perpendicularly Magnetized Magnetic Layers Using Spin Torque from the Spin Hall Effect. Physical Review Letters 109, 096602, (2012). 4. Mellnik, A. R. et al. Spin-transfer torque generated by a topological insulator. Nature 511, 449-451, (2014). 5. MacNeill, D. et al. Control of spin-orbit torques through crystal symmetry in WTe2/ferromagnet bilayers. Nature Physics 13, 300-305, (2017). 6. Xue, F. et al. Unconventional spin-orbit torque in transition metal dichalcogenide--ferromagnet bilayers from first-principles calculations. Physical Review B 102, 014401, (2020).