Probing Spin-Orbit Torque Switching Through Unidirectional Magnetoresistance
Chi-Feng Pai, National Taiwan University
August 18, 2020
It has been shown that the spin Hall effect (SHE) from heavy transition metals and other emergent materials systems can generate sufficient spin-orbit torque (SOT) and further produce current-induced magnetization switching in the adjacent ferromagnetic layer. However, if the ferromagnetic layer has in-plane magnetic anisotropy, probing such switching phenomenon typically relies on tunnelling magnetoresistance (TMR) measurement of nano-sized magnetic tunnel junctions (challenging in device making), differential planar Hall voltage (DPHE) measurement (complicated in measurement configuration), or Kerr imaging approaches (relies on optical response). In this presentation, I will first show that in magnetic heterostructures with spin Hall metals, there exist current-induced in-plane spin Hall effective fields (SHF)  and unidirectional magnetoresistance (UMR)  that will modify their anisotropic magnetoresistance behaviour. By analysing the response of magnetoresistance under such influences, one can directly and electrically probe magnetization switching driven by the spin-orbit torque, even in common micron-sized Hall-bar devices. This pump-probe method therefore allows for efficient and direct determination of key parameters from spin-orbit torque switching events without lengthy device fabrication processes .
 X. Fan, J. Wu, Y. Chen, M. J. Jerry, H. Zhang, and J. Q. Xiao, Observation of the nonlocal spin-orbital effective field, Nat. Commun. 4, 1799 (2013).
 C. O. Avci, K. Garello, A. Ghosh, M. Gabureac, S. F. Alvarado, and P. Gambardella, Unidirectional spin Hall magnetoresistance in ferromagnet/normal metal bilayers, Nat. Phys. 11, 570 (2015).
 Y.-T. Liu, T.-Y. Chen, T.-H. Lo, T.-Y. Tsai, S.-Y. Yang, Y.-J. Chang, J.-H. Wei, and C.-F. Pai, Determination of Spin-Orbit Torque Efficiencies in Heterostructures with In-plane Magnetic Anisotropy, Physical Review Applied 13, 044032 (2020).