Spin–orbit torques (SOTs) in multilayers of ferromagnetic (FM) and non-magnetic (NM) metals can manipulate the magnetization of the FM layer efficiently. This is employed, for example, in non-volatile magnetic memories for energy-efficient mobile electronics1,2 and spin torque nano-oscillators3,4,5,6,7 for neuromorphic computing8. Recently, spin torque nano-oscillators also found use in microwave-assisted magnetic recording, which enables ultrahigh-capacity hard disk drives9. Most SOT devices employ spin Hall10,11 and Rashba12 effects, which originate from spin–orbit coupling within the NM layer and at the FM/NM interfaces, respectively. Recently, SOTs generated by the anomalous Hall effect in FM/NM/FM multilayers were predicted13 and experimentally realized14. The control of SOTs through crystal symmetry was demonstrated as well15. Understanding all the types of SOTs that can arise in magnetic multilayers is needed for a formulation of a comprehensive SOT theory and for engineering practical SOT devices. Here we show that a spin-polarized electric current known to give rise to anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in a FM16 can additionally generate large antidamping SOTs with an unusual angular symmetry in NM1/FM/NM2 multilayers. This effect can be described by a recently proposed magnonic mechanism17. Our measurements reveal that this torque can be large in multilayers in which both spin Hall and Rashba torques are negligible. Furthermore, we demonstrate the operation of a spin torque nano-oscillator driven by this SOT. These findings significantly expand the class of materials that exhibit giant SOTs.
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We thank M. Arora and E. Girt for discussion on the Co/Ni multilayer growth. Work on the deposition of the magnetic multilayers was supported as part of the Spins and Heat in Nanoscale Electronic Systems (SHINES), an Energy Frontier Research Centre funded by the US Department of Energy, Office of Basic Energy Sciences under Award no. DE-SC0012670. Nanowire device fabrication was supported by the US Department of Energy, Office of Basic Energy Sciences under Award no. DE-SC0014467. Spin torque oscillator development was supported by the National Science Foundation under Award no. DMR-1610146. Work on the variable-angle ST-FMR set-up development was supported by the National Science Foundation under Award no. EFMA-1641989. ST-FMR characterization was supported by the Army Research Office under Award no. W911NF-16-1-0472. Work on the absorptive FMR and spin pumping measurements was supported by the Defence Threat Reduction Agency under Award no. HDTRA1-16-1-0025. Work on experiment design and SOT analysis was supported by the National Science Foundation under Award no. ECCS-1708885.
The authors declare no competing interests.
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Safranski, C., Montoya, E.A. & Krivorotov, I.N. Spin–orbit torque driven by a planar Hall current. Nature Nanotech 14, 27–30 (2019). https://doi.org/10.1038/s41565-018-0282-0
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