Anomalous spin-orbit torques in magnetic single-layer films

Wenrui Wang; Tao Wang; Vivek P Amin; Yang Wang; Anil Radhakrishnan; Angie Davidson; Shane R Allen; T J Silva; Hendrik Ohldag; Davor Balzar; Barry L Zink; Paul M Haney; John Q Xiao; David G Cahill; Virginia O Lorenz; Xin Fan

doi:10.1038/s41565-019-0504-0

Anomalous spin-orbit torques in magnetic single-layer films

Nat Nanotechnol. 2019 Sep;14(9):819-824. doi: 10.1038/s41565-019-0504-0. Epub 2019 Jul 22.

Authors

Wenrui Wang¹, Tao Wang², Vivek P Amin^{3

4}, Yang Wang², Anil Radhakrishnan¹, Angie Davidson⁵, Shane R Allen⁵, T J Silva⁶, Hendrik Ohldag⁷, Davor Balzar⁵, Barry L Zink⁵, Paul M Haney⁴, John Q Xiao², David G Cahill⁸, Virginia O Lorenz⁹, Xin Fan¹⁰

Affiliations

¹ Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
² Department of Physics and Astronomy, University of Delaware, Newark, DE, USA.
³ Maryland Nanocenter, University of Maryland, College Park, MD, USA.
⁴ Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD, USA.
⁵ Department of Physics and Astronomy, University of Denver, Denver, CO, USA.
⁶ Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, CO, USA.
⁷ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
⁸ Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
⁹ Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, USA. vlorenz@illinois.edu.
¹⁰ Department of Physics and Astronomy, University of Denver, Denver, CO, USA. xin.fan@du.edu.

PMID: 31332346
DOI: 10.1038/s41565-019-0504-0

Abstract

The spin Hall effect couples charge and spin transport^1-3, enabling electrical control of magnetization^4,5. A quintessential example of spin-Hall-related transport is the anomalous Hall effect (AHE)⁶, first observed in 1880, in which an electric current perpendicular to the magnetization in a magnetic film generates charge 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. We interpret the ASOT as being due to a spin-Hall-like current generated with an efficiency of 0.053 ± 0.003 in Ni₈₀Fe₂₀, comparable to the spin Hall angle of Pt⁷. Similar effects are also observed in other common ferromagnetic metals, including Co, Ni and Fe. First-principles calculations corroborate the order of magnitude of the measured values. This work suggests that a strong spin current with spin polarization transverse to the magnetization can be generated within a ferromagnet, despite spin dephasing⁸. The large magnitude of the ASOT should be taken into consideration when investigating spin-orbit torques in ferromagnetic/non-magnetic bilayers.