Absence of Thermal Hall Effect in Anomalous Nernst and Spin Seebeck Effects
Yi-Jia Chen1*, Ssu-Yen Huang1
1Department of Physics, National Taiwan University, Taipei, Taiwan
* presenting author:Yi-Jia Chen, email:b00202073@ntu.edu.tw
Anomalous Nernst effect (ANE) and spin-Seebeck effect (SSE) in spin caloritronics are two of the most important mechanisms to manipulate the spin-polarized and pure spin current respectively by thermal excitation. While the ANE in ferromagnetic metals and the SSE in magnetic insulators have been extensively studied, a recent theoretical work suggests that the thermal Hall effect (THE), including magnon Hall effect and anomalous Righi-Leduc effect, have been overlooked, and they may significantly contribute to the ANE and SSE. [2] Most strikingly, the THE, which results in the anisotropic transverse temperature gradient, has the exact same magnetic-field angular dependence as the ANE and SSE. This anisotropic transverse temperature gradient can be converted into an electric signal by the thermocouple effect. In this work, we experimentally demonstrate that the thermocouple effect in the ANE and SSE measured geometry is indeed inevitable for studying thin films. [2] By designing special measured geometries with high temperature sensitivity, we are able to systematically study the THE by the thermocouple effect in the ferromagnetic metal, permalloy (Py), and the magnetic insulator, yttrium iron garnet (YIG). Our results demonstrate that the contribution of the THE by thermal couple effect in the Py and YIG is negligibly small, if one includes the thickness dependence of the Seebeck coefficient. Thus, the spin-polarized current in ANE and the pure spin current in SSE remain indispensable for exploring spin caloritronics phenomena.

Reference: [1] J.-E. Wegrowe, and H.-J. Drouhin, and D. Lacour. Phys. Rev. B 89, 094409 (2014).
[2] Y. J. Chen and S. Y. Huang, Phys. Rev. Lett, in press (2016).

Keywords: Thermal Hall Effect, Anomalous Nernst Effect, Spin Seebeck Effect, Thermocouple, Seebeck Coefficient