Ferromagnetic Resonance Study of Interfacial Exchange Coupling in Topological Insulator/Ferrimagnetic Insulator Heterostructure
Y. T. Fanchiang1*, H. Y. Lin2, C. C. Tseng2, K. S. Chen2, C. N. Wu2, C. K. Cheng1, S. F. Lee3, J. G. Lin4, M. Hong1, J. Kwo2
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
3Institute of Physics, Academia Sinica, Taipei, Taiwan
4Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
* presenting author:Yu-Ting Fan-Chiang, email:ytfanchiang@gmail.com
Introducing magnetic order in topological insulators via magnetic proximity coupling when in contact with a ferrimagnet is a promising way to realize novel topological physics such as quantum anomalous Hall effect. In this work, we have performed ferromagnetic resonance (FMR) of heterostructures made of yttrium iron garnet (YIG) films of varying thickness (15-30 nm) and Βi₂Se₃ films (25 QL) from 300K down to 5 K. Frequency- and angle-dependence FMR show sizable Βi₂Se₃-induced effective field in bilayer samples at room temperature, which is manifested as enhanced in-plane magnetic anisotropy over that of single layer YIG. The origin of such magnetic anisotropy occurring at interface is clarified by the YIG thickness dependence study. As the temperature decreases, the exchange effective field builds up pronouncedly and the FMR remains detectable. Specifically, for the bilayer sample of thin YIG (15 nm), the exchange effective field can induce FMR at microwave frequency of at least 3.5 GHz in absence of applied field below 50 K. Our study reveals the role of strong interfacial exchange coupling between Βi₂Se₃ and YIG in magnetization dynamics, leading to potential field-free spintronics application.

Keywords: topological insulator, magnetic insulator, magnetic anisotropy, spin pumping