Spin-orbit torques (SOTs) enable the energy-efficient manipulation of magnetization by electric current which is promising for future information technology – with applications in non-volatile memory [1], microwave-assisted magnetic recording [2], spin torque nano-oscillators (STNO) [3], and neuromorphic computing [4]. SOTs can be generated in bilayers of ferromagnetic (FM) and non-magnetic (NM) materials with broken inversion symmetry. The most explored SOTs are the spin Hall torque originating from spin-orbit coupling in in NM layers [5] and the Rashba torque induced by spin-orbit coupling at NM/FM interfaces [6]. Recently, we have demonstrated that the planar Hall current in a FM can lead to a giant SOT applied to the same FM [7], an example of a new class of self-generated spin orbit torques. In this talk, I will report the discovery of a giant self-generated SOT induced by anomalous Hall current in FM conductors. This anomalous Hall torque displays an unusual angular symmetry that is distinct from the previously discovered spin Hall, Rashba, and planar Hall torques. We demonstrate that the strength of the anomalous Hall SOT can be tuned by filling of the FM electronic bands in the same manner as the AHE magnitude [8]. Finally, we demonstrate a new type of spin torque oscillator ­– the anomalous Hall nano-oscillator.

[1]    N. Sato, F. Xue, R. M. White, C. Bi, and S. X. Wang, Two-Terminal Spin–Orbit Torque Magnetoresistive Random Access Memory, Nature Electronics 1, 9 (2018).

[2]    H. T. Nembach, P. Martín Pimentel, S. J. Hermsdoerfer, B. Leven, B. Hillebrands, and S. O. Demokritov, Microwave Assisted Switching in a Ni81Fe19 Ellipsoid, Appl. Phys. Lett. 90, 062503 (2007).

[3]    M. Haidar, A. A. Awad, M. Dvornik, R. Khymyn, A. Houshang, and J. Åkerman, A Single Layer Spin-Orbit Torque Nano-Oscillator, Nature Communications 10, 1 (2019).

[4]    J. Grollier, D. Querlioz, K. Y. Camsari, K. Everschor-Sitte, S. Fukami, and M. D. Stiles, Neuromorphic Spintronics, Nat Electron 3, 360 (2020).

[5]    L. Liu, C.-F. Pai, Y. Li, H. W. Tseng, D. C. Ralph, and R. A. Buhrman, Spin-Torque Switching with the Giant Spin Hall Effect of Tantalum, Science 336, 555 (2012).

[6]    I. Mihai Miron, G. Gaudin, S. Auffret, B. Rodmacq, A. Schuhl, S. Pizzini, J. Vogel, and P. Gambardella, Current-Driven Spin Torque Induced by the Rashba Effect in a Ferromagnetic Metal Layer, Nature Mater 9, 230 (2010).

[7]    C. Safranski, E. A. Montoya, and I. N. Krivorotov, Spin–Orbit Torque Driven by a Planar Hall Current, Nature Nanotech 14, 1 (2019).

[8]    Z. Shi, H.-Y. Jiang, S.-M. Zhou, Y.-L. Hou, Q.-L. Ye, and M. Su Si, Effect of Band Filling on Anomalous Hall Conductivity and Magneto-Crystalline Anisotropy in NiFe Epitaxial Thin Films, AIP Advances 6, 015101 (2016).