Ferrimagnetic insulators, such as yttrium iron garnet, have ultralow damping and are free of electronic Joule heating, promising an ultralow-power information channel for future spintronic circuits. However, the memory applications based on magnetic insulators have been halted for decades since the hot pursuit of magnetic bubble memory in the last seventies due to two major challenges: magnetic field control and large bubble size. Electrical control of magnetization in magnetic insulators is thought to be impossible due to their insulating nature. Recently, spin-orbit torques (SOTs) from heavy metals have emerged to become an efficient way to manipulate magnetization of adjacent magnetic insulators [1-3]. Besides, topological magnetic skyrmions in magnetic insulators could be potentially scaled to nanoscale size [4]. However, it has been only observed at cryogenic temperatures.

In this talk, I will first present our demonstration of SOT-driven magnetization switching of a 15 nm-thick magnetic insulator [3]. Our detailed magnetization and SOT measurements reveal an interfacial magnetization-dependent SOT. Moreover, efficient SOT-driven magnetization switching is demonstrated in a ferrimagnetic insulator across the compensation temperature. Then, I will present our observation of high-temperature topological Hall effect (THE) in heavy metal/ferrimagnetic insulator heterostructures [5]. The dependence of THE on temperature, magnetic anisotropy, out-of-pane magnetic field, in-plane bias field, the type of heavy metal, and magnetic insulator thickness suggest the existence of chiral Dzyaloshinskii–Moriya interaction (DMI) at the heavy metal/magnetic insulator interface and the magnetic skyrmions.  Similar results are reported in refs. [6-8]. The demonstrations of efficient SOT manipulation and chiral spin orders in heavy metal/ferrimagnetic insulator heterostructures provide a valuable platform for exploring magnetic insulator-based memory devices.

[1] P. Li et al., Nat Commun 7, 12688 (2016).
[2] C. O. Avci, A. Quindeau, C. F. Pai, M. Mann, L. Caretta, A. S. Tang, M. C. Onbasli, C. A. Ross, and G. S. Beach, Nature Mater. 16, 309 (2017).
[3] Q. Shao et al., Nat Commun. 9, 3612 (2018).
[4] S. Seki, X. Z. Yu, S. Ishiwata, and Y. Tokura, Science 336, 198 (2012).
[5] Q. Shao et al., Nature Electronics 2, 182 (2019).
[6] C. O. Avci, E. Rosenberg, L. Caretta, F. Buttner, M. Mann, C. Marcus, D. Bono, C. A. Ross, and G. S. D. Beach, Nature Nanotech. 14, 561 (2019).
[7] A. J. Lee, A. S. Ahmed, J. Flores, S. Guo, B. Wang, N. Bagues, D. W. McComb, and F. Yang, Phys. Rev. Lett. 124, 107201 (2020).
[8] A. S. Ahmed et al., Nano Lett. 19, 5683 (2019).