Spin Current Generated by the Thermal Transport
Ssu-Yen Huang1*
1Department of Physics, National Taiwan University, Taipei, Taiwan
* Presenter:Ssu-Yen Huang, email:syhuang@phys.ntu.edu.tw
The anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE) in spin caloritronics are two of the most important mechanisms to manipulate the spin-polarized current and pure spin current by thermal excitation and have been extensively studied. However, we experimentally demonstrate that the thermocouple effect associated with the thermal Hall effect (THE) in the ANE and SSE measured geometry is inevitable. [1] The THE, which results in the anisotropic transverse temperature gradient, has a magnetic field dependence indistinguishable from, and may even overwhelm, those of the ANE and SSE. Therefore, it is vital to investigate the contribution of the THE in the ANE and SSE.

In this work [1], we are able to study the separation of the THE, SSE, and ANE in the ferromagnetic metal and the magnetic insulator by designing several special measured geometries associated with the thermocouple effect. Our results show that the contribution of the THE by thermocouple effect in the permalloy (Py) and yttrium iron garnet (YIG) is negligibly small. The spin-polarized current in the ANE and the pure spin current in the SSE remain important elements for exploring spin caloritronics phenomena. In addition, when a temperature gradient builds across the interface between a spin Hall metal and a magnetic insulator, the spin-dependent voltage excited by the heat current can be a very useful tool to explore the surface magnetization of the magnetic materials. [2] Most importantly, the spin current excited by the SSE is surprisingly insensitive to crystal structures of the material. Consequently, the pure spin current generated by the SSE is robust and fights against the poor crystallinity. [3] In this talk, I will also discuss the generation of the thermal spin current from the ferromagnetic metals. [4]

[1] Y. J. Chen and S. Y. Huang, Phys. Rev. Lett. 117, 247201 (2016).
[2] P. H. Wu and S. Y. Huang, Phys. Rev. B. 94, 024405 (2016).
[3] Feng-Jen Chang, Jauyn Grace Lin, and Ssu-Yen Huang, Phys. Rev. Materials 1, 031401(R) (2017).
[4] Bo-Wei Wu, G. Y. Luo, J. G. Lin, and Ssu-Yen Huang, Phys. Rev. B 96, 060402 (R) (2017).

Keywords: pure spin current, spin-polarized current, spin Seebeck effect, anomalous Nernst effect, spin caloritronics