Switching of Perpendicular Magnetization by Spin-Orbit Torque

Electrical switching of magnetization is central to spintronic memory and computing. Despite the enormous investigations in the past two decades, the understanding of spin-orbit torque and the switching of perpendicular magnetization remains elusive as indicated by a number of remarkable long-standing puzzles (see [1,2] for reviews of this problem in thin-film and van der Waals systems). First, this talk will show that the spin-orbit torque is not simply an interfacial spin transfer effect but varies strongly with the relative spin relaxation rates within the magnetic layer, such that a given spin-current generator can exert the strongest spin-orbit torque on 3<i>d</i> ferromagnets but much weaker one on nearly compensated ferrimagnets [3]. This talk will also discuss that, in many spin-orbit torque (SOT) heterostructures, such as heavy metal/ferromagnet bilayers with perpendicular magnetic anisotropy (PMA), the scaling of the switching current density with the SOT and the applied magnetic field is in strong disagreement with the predictions of the existing macrospin and chiral-domain-wall depinning models [4]. These remarkable puzzles can, in most cases, be explained by the long-range intralayer Dzyaloshinskii-Moriya interaction effect in magnetic heterostructures [5].<br/><br/><b>Reference</b><br/>[1] L. Zhu, Switching of Perpendicular Magnetization by Spin-Orbit Torque, Adv. Mater. 35, 2300853 (2023).<br/>[2] X. Lin, L. Zhu*, Magnetization switching in van der Waals systems by spin-orbit torque, Materials Today Electronics 4, 100037 (2023).<br/>[3] L. Zhu*, D.C. Ralph, Strong variation of spin-orbit torques with relative spin relaxation rates in ferrimagnets, Nat. Commun. 14, 1778 (2023).<br/>[4] L. Zhu*, D. C. Ralph, and R. A. Buhrman, Lack of Simple Correlation between Switching Current Density and Spin-Orbit-Torque Efficiency of Perpendicularly Magnetized Spin-Current-Generator–Ferromagnet Heterostructures, Phys. Rev. Appl. 15, 024059 (2021).<br/>[5] Q. Liu, L. Liu, G. Xing, L. Zhu*, Asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction, Nat. Commun. 15, 2978 (2024).