Spin-orbit torque ferromagnetic resonance in transferred-topological insulator/normal metal/ferromagnetic metal heterostructure

Yu Chi Liu^1*, Chun Chia Chen¹, Shang Rong Yang¹, Sheng Wen Huang¹, Liang Juan Chang², Shang Fan Lee², Minghwei Hong³, J. Raynien Kwo¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Institute of Physics, Academia Sinica, Taipei, Taiwan
³Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan

* Presenter:Yu Chi Liu, email:yukiphys2009@gmail.com

Topological insulators (TIs) have been commonly synthesized with ferromagnet (FM) for the purpose of investigating its spin-to-charge conversion generated by the spin-momentum locking property in the TI surface state (TISS). Although large amount of work has been carried out in this kind of bi-layer structure, it has been pointed out that severe chemical interaction may occur at the interface of TI and FM. On the other hand, it also has been theoretically shown that TISS can be drastically disturbed in conjunction with a FM. In this work, we provide a special sample preparation process to circumvent these issues. We applied the TI transferring technique on the MBE-grown Bi₂Se₃/Sapphire thin film. The exfoliated Bi₂Se₃ were transferred onto the Au/Py bilayer. We then obtained the spin torque ratio evaluated from the spin-orbit torque ferromagnetic resonance (ST-FMR) line shape analysis. Remarkably, the value was enhanced by around 90% (from 0.027-0.051) in transferred-Bi₂Se₃/Au/Py sample compared to the reference sample, Au/Py. Moreover, the value further increased by around 300% (0.11) after annealing process under high vacuum environment, which can be due to the improved adhesion between Bi₂Se₃ and Au. Our result suggests a spin current can be generated from the TISS and exert an additional anti-damp like torque onto Py across the Au interlayer. The ST-FMR investigation on the transferred-TI/Au/FM tri-layer heterostructure may shed light on the spintronic application based on TISS-induced spin torque with a more chemically abrupt interface than previous work.

Keywords: spin-orbit torque , ferromagnetic resonance, topological insulator, thin film transferring