BC-07: Magneto-Ionic Control of Perpendicular Magnetic Anisotropy for Energy-Efficient Spintronic Devices

Magnetic materials with switchable magnetic domains and anisotropy are the key to energy-efficient spintronic devices [1]. Magnetization switching of ferromagnets can be achieved through a spin-orbit torque (SOT) generated using materials that have large charge-to-spin efficiencies, such as heavy metals. Some ferromagnets, such as Weyl semi-metal Co2MnGa, have a large spin Hall angle [2] and can themselves generate sizeable SOTs [3]. In such materials, the magnetization direction determines the spin current and spin polarization directions [4], allowing for the possibility to control SOT by adjusting the magnetic anisotropy and hence the magnetization direction. Here, we will present the ionic liquid gating (Fig. 1a) switching of perpendicular magnetic anisotropy (PMA) of thin layers of stacks containing a conventional ferromagnet Ta/CoFeB/W and a ferromagnet Weyl semi-metal MgO/Co2MnGa/Pd. Measurements were achieved with a magneto-optical Kerr effect (MOKE) system. A positive voltage causes CoFeB to completely switch from perpendicular to in-plane anisotropy (Fig. 1b), whereas a negative voltage is required to reduce the anisotropy of Co2MnGa, and it does not fully switch to in-plane (Fig. 1c). The CoFeB anisotropy change is reversible upon removing the voltage, but the Co2MnGa cannot be reversed even with a reversed voltage. The relative slowness of the changes (~ seconds to hours) and the reversed-sign behaviour of the films show that the origin of the anisotropy change is magnetoionic, i.e. due to the change in oxidation state of the samples.References: [1] A. Davidson, V. P. Amin, W. S. Aljuaid, P. M. Haney, and X. Fan, “Perspectives of electrically generated spin currents in ferromagnetic materials,” Phys. Lett. A, vol. 384, no. 11, p. 126228, 2020, doi: 10.1016/j.physleta.2019.126228. [2] L. Leiva, S. Granville, Y. Zhang, S. Dushenko, E. Shigematsu, T. Shinjo, R. Ohshima, Y. Ando, and M. Shiraishi, "Giant spin Hall angle in the Heusler alloy Weyl ferromagnet Co2MnGa", Phys. Rev. B, vol. 103, L04114, 2021, doi: 10.1103/PhysRevB.103.L041114. [3] K. Tang, Z. Wen, Y. C. Lau, H. Sukegawa, T. Seki, and S. Mitani, “Magnetization switching induced by spin-orbit torque from Co2MnGa magnetic Weyl semimetal thin films,” Appl. Phys. Lett., vol. 118, no. 6, 2021, doi: 10.1063/5.0037178. [4] T. C. Chuang, D. Qu, S. Y. Huang, and S. F. Lee, “Magnetization-dependent spin Hall effect in a perpendicular magnetized film,” Phys. Rev. Res., vol. 2, no. 3, pp. 2–6, 2020, doi: 10.1103/PhysRevResearch.2.032053.