Spin-orbit Torque and Magnetoresistance Phenomena in Layered Quantum Materials
Department of Physics, Carnegie Mellon University
Layered quantum materials, such as WTe2 and MoTe2, host plethora of novel phenomena that are highly relevant for quantum spintronics, namely: Dirac type dispersion, strong spin-orbit coupling (SOC), Fermi arcs, and helical spin-momentum locked surface and bulk states. These systems provide a distinct opportunity to obtain highly efficient and unconventional charge to spin conversion owing to strong SOC, symmetry breaking, and these topology-based phenomena. On the other hand, spin-orbit torque (SOT) driven deterministic control of the magnetic state of a ferromagnet with perpendicular magnetic anisotropy is key to next generation spintronic applications including non-volatile, ultrafast, and energy efficient data storage devices. But field-free deterministic SOT switching of perpendicular magnetization remains a challenge because it requires an out-of-plane oriented spin current, which is not allowed in conventional spin source materials, such as heavy metals and topological insulators due to the system symmetry. The exploitation of low-crystal symmetries WTe2 and MoTe2 offers a unique approach to achieve SOTs with unconventional forms1. In this talk, I will discuss our experiments to realize field-free deterministic magnetic switching of a perpendicularly polarized van der Waals magnet employing an out-of-plane spin current generated in layered WTe2, which is a quantum material with low-symmetry crystal structure2. I will also discuss our recent experiments aimed at achieving field-free SOT switching of insulating FMs using spin current in layered materials and observation of new type of magnetoresistance effect in bilayer systems of WTe2 and layered magnets.
. MacNeill, D. et al. Control of spin–orbit torques through crystal symmetry in WTe2/ferromagnet bilayers. Nature Physics 13, 300-305, (2017).
. Kao, I-H et al. Deterministic switching of a perpendicularly polarized magnet using unconventional spin–orbit torques in WTe2. Nature Materials (2022). https://doi.org/10.1038/s41563-022-01275-5
Host: Shulei Zhang