Anomalous spinorbit torques in magnetic single-layer films
Wenrui Wang, Tao Wang, Vivek P. Amin, Yang Wang, Anil Radhakrishna, Angie Davidson, Shane Allen, Thomas J. Silva, Hendrik Ohldag, Davor Balzar, Barry L. Zink, Paul M. Haney, John Xiao, D.G. Cahill, Virginia O. Lorenz, Xin Fan
Spin-orbit interaction (SOI) couples charge and spin transport, enabling electrical control of magnetization, the foundation of next-generation spintronic devices. A quint essential example of SOI-induced transport is the anomalous Hall effect (AHE), first observed in 1880, in which an electric current perpendicular to the magnetization in a magnetic film generates charge and spin accumulation on the surfaces. Here we report the observation of a counterpart of the AHE that we term the anomalous spin-orbit torque (ASOT), wherein an electric current parallel to the magnetization generates opposite spin-orbit torques on the surfaces of the magnetic film. Using the magneto-optic Kerr effect to measure the current-induced out-of-plane magnetization tilt, we extract the ASOT efficiency of a single layer Ni80Fe20 film to be 0.055 +/- 0.005, comparable to the spin Hall angle of Pt, and observe similar effects in other common ferromagnetic metals, including Co, Ni, and Fe. First principles calculations corroborate the order of magnitude of the measured values. This work leads to the conclusion that a single- layer ferromagnet can generate spin-orbit torques on its own surfaces, challenging the current understanding of spin-orbit torque in magnetic/nonmagnetic bilayers and introducing a new route for electrically manipulating magnetization in magnetic nanodevices.