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

Cornell Affiliated Author(s)

Author

D. Macneill
G. Stiehl
Marcos Guimarães
Robert Buhrman
J. Park
D. Ralph

Abstract

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 WTe 2 , 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 WTe 2 /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. © 2017 Macmillan Publishers Limited.

Date Published

Journal

Springer Science and Business Media LLC

Volume

13

Issue

3

Number of Pages

300-305,

URL

https://www.scopus.com/inward/record.uri?eid=2-s2.0-84994608141&doi=10.1038%2fnphys3933&partnerID=40&md5=5b693b8dbd6cbfe0239da4a1f5c99f27

DOI

10.1038/nphys3933

Funding Source

DGE-1144153
DMR-1120296
DMR-1539918
ECCS-1542081
NWO 680-50-1311
1406333
1539918
DMR-1406333
W911NF-15-1-0447
680-50-1311

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