Control of spin–orbit torques through crystal symmetry in WTe2/ferromagnet bilayers

By David MacNeill, G. Stiehl, M. Guimarães, Robert A. Buhrman, Jiwoong Park, D. Ralph. Nature Physics, 2016

741 citations recorded by the source corpus.

Recent discoveries regarding current-induced spin–orbit torques produced by heavy-metal/ferromagnet and topological-insulator/ferromagnet bilayers provide the potential for dramatically improved efficiency in the manipulation of magnetic devices. However, in experiments performed to date, spin–orbit torques have an important limitation—the component of torque that can compensate magnetic damping is required by symmetry to lie within the device plane. This means that spin–orbit torques can drive the most current-efficient type of magnetic reversal (antidamping switching) only for magnetic devices with in-plane anisotropy, not the devices with perpendicular magnetic anisotropy that are needed for high-density applications. Here we show experimentally that this state of affairs is not fundamental, but rather one can change the allowed symmetries of spin–orbit torques in spin-source/ferromagnet bilayer devices by using a spin-source material with low crystalline symmetry. We use WTe2, a transition-metal dichalcogenide whose surface crystal structure has only one mirror plane and no two-fold rotational invariance. Consistent with these symmetries, we generate an out-of-plane antidamping torque when current is applied along a low-symmetry axis of WTe2/Permalloy bilayers, but not when current is applied along a high-symmetry axis. Controlling spin–orbit torques by crystal symmetries in multilayer samples provides a new strategy for optimizing future magnetic technologies. A link between crystalline symmetry and the allowed symmetries of spin–orbit torques provides a route for manipulating magnetic devices with perpendicular anisotropy.

Subfields: Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials

View Paper: https://www.semanticscholar.org/paper/90ee90aaf05662225a349b1cb131dd62663aa0d8

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Citations in the corpus

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems (2018, positive): “, 2016c) and on the semi-metal WTe2 (MacNeill et al., 2017).”
Magnetism, symmetry and spin transport in van der Waals layered systems (2021, positive): “There are several studies that show how symmetries affect the magnetization dynamics through a 2D layer inserted at an interface 122,123,127,162–166 .”
Interface-Induced Phenomena in Magnetism (2016, positive): “, lacking twofold rotational symmetry about the out-ofplane axis) so that an out-of-plane antidamping torque becomes symmetry allowed (MacNeill et al., 2016).”
Tilted spin current generated by the collinear antiferromagnet ruthenium dioxide (2021, methodology): “We will refer to a non-trivial spin Hall torque with a well-defined spin orientation ŝ (and therefore following the signature angular dependence in equations (1) to (3)) as an AF-SHE for either the T -odd or T -even mechanism.”
Quantum materials for spin and charge conversion (2018, methodology): “m a real-space Berry phase effect despite almost zero net magnetization128-134. Chen et al133 performed the calculation on IrMn3, of which Mn sublattices consist of 2D kagome lattices viewed from its (111) direction. They theoretically demonstrate that a large anomalous Hall effect exists, arising f”