Unconventional Spin Hall Effect in Magnet

Danru Qu^1,2*, Tsao-Chi Chuang³, Shang-Fan Lee², Ssu-Yen Huang³

¹Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
²Institute of Physics, Academia Sinica, Taipei, Taiwan
³Department of Physics, National Taiwan University, Taipei, Taiwan

* Presenter:Danru Qu, email:danru@ntu.edu.tw

The discovery of the spin Hall effect (SHE) and the inverse spin Hall effect (ISHE) marks the new era of the pure-spin-current-based spintronic explorations. With the advantage of minimum charge carrier but maximum angular momentum, the pure spin current has already found its importance in the spin-orbit torque magnetic random access memory devices.
In SHE, a spin current is generated in the transverse direction out from the charge current, and the charge current, the spin current, and the spin polarization are mutually orthogonal. As a result, the spin current accumulated at a film surface always has spin polarization oriented in the film plane, making the magnetization switching of an attached magnet with perpendicular magnetization difficult. Excitingly, reports have shown that this restriction can be lifted through the magnetization-dependent spin Hall effect (MDSHE) in magnetic materials [1, 2], where the charge-induced spin polarization is additionally manipulated by the magnetization directions, opening new perspectives for spintronics. Nevertheless, the existing reports of the MDSHE have various competing contributions and artifacts due to their all metallic heterostructures. As a result, experimentally, the MDSHE remains unequivocally established, not to mention the quantitative analyses.
In this talk, I will discuss our approach to unambiguously establishing the MDSHE. We utilize the magnetic insulator YIG to thermally inject pure spin current into a perpendicular magnetized Pt/Co/Pt layer. We exclude the occurrence of any possible artifact and clearly demonstrate that the spin polarization of pure spin current induced by the MDSHE could be arbitrarily and independently controlled by the magnetization direction. Furthermore, we explicitly identify the strength of the MDSHE, compare its size with the SHE, and further estimate the magnetic spin Hall angle to be -0.36%. Our approach provides a versatile and controllable route to explore the unconventional spin and charge conversions in magnetic materials and benefit next-generation spintronic applications.

[1] A. M. Humphries, et al., Nat. Commun. 8, 911 (2017)
[2] M. Kimata, et al., Nature 565, 627 (2019)
[3] T. C. Chuang, et al., Phys. Rev. Research 2, 032053(R) (2020)

Keywords: spin current, spin Hall Effect , magnetization dependent spin Hall effect, perpendicular magnetization