Spin-orbit torque driven by a planar Hall current

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 electronics^1,2 and spin torque nano-oscillators^3-7 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 Hall^10,11 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.