Spin current transport in an insulating antiferromagnet makes possible the observation of the spin Seebeck effect in permalloy separated from the anomalous Nernst effect*

The spin Seebeck effect (SSE) refers to the generation of a spin current by a temperature gradient in a magnetic material [1]. In the longitudinal configuration (LSSE) the SSE has been studied quatitatively only in magnetic insulators because in metallic films it is contaminated by the anomalous Nernst effect (ANE) [1]. We will present theoretical and experimental studies of the LSSE in the metallic ferromagnet N₈₁Fe₁₉ (permalloy-Py) separated from the ANE in trilayer samples of Py/NiO/NM (NM is a normal metal, Pt or Ta) under a temperature gradient perpendicular to the plane. The spin current due to SSE in Py that is transported across the NiO layer and reaches the NM layer, where it is converted into a charge current by the inverse spin Hall effect. The LSSE is detected by a voltage in the NM layer while the ANE is measured by the voltage induced in the Py layer. The separation of the two effects is made possible because the insulating AF layer of NiO transports spin current by magnon diffusion while providing electrical insulation between the Py and NM layers [2-5]. The measured spin Seebeck coefficient for Py has a value similar to the one for the ferrimagnetic insulator yttrium iron garnet, with the same sign, and is in good agreement with the value calculated with a thermoelectric spin diffusion model [6].
[1] K. Uchida, H. Adachi, T. Kikkawa, A. Kirihara, M. Ishida, S. Yorozu, S. Maekawa, and E. Saitoh, Proc. IEEE 104, 1946 (2016).
[2] C. Hahn, G. de Loubens, V. V. Naletov, J. Ben Youssef, O. Klein, and M. Viret, Europhys. Lett. 108, 57005 (2014).
[3] H. Wang, C. Du, P. C. Hammel, and F. Yang, Phys. Rev. B 91, 220410(R) (2015).
[4] W. Lin, K. Chen, S. Zhang, and C. L. Chien, Phys. Rev. Lett. 116, 186601 (2016).
[5] S. M. Rezende, R. L. Rodríguez-Suárez, and A. Azevedo, Phys. Rev. B 93, 054412 (2016).
[6] J. Holanda et. al., Phys. Rev. B 95, 214421 (2017).