Intrinsic Spin Seebeck Effect in Gold

In Spin Seebeck Effect (SSE), a pure spin current can be generated by a temperature gradient ($\nabla $T) and detected by the inverse spin Hall effect usually by Pt. Due to the propensity of out-of-plane $\nabla _{\mathrm{z}}$T through substrate, the SSE in the transverse configuration with an in-plane $\nabla_{\mathrm{x}}$T has been shown contaminated by the anomalous Nernst effect.\footnote{S. Y. Huang, et al. Phys. Rev. Lett. 107, 216604 (2011)} The SSE in the longitudinal configuration with $\nabla_{\mathrm{z}}$T suffers from the magnetic proximity effect (MPE) of Pt in contact with a ferromagnetic material thus also contaminated.\footnote{S. Y. Huang, et al. Phys. Rev. Lett. 109, 107204 (2012)} In this work, we demonstrate that Au does not exhibit MPE and reveals the intrinsic SSE. In contrast to Pt/YIG, Au/YIG shows no anomalous Hall signals, very weak inverse MR, and non-monotonic thickness dependence of spin thermal voltage, thus very weak if any MPE. Our results place an upper limit to the intrinsic SSE of 0.1$\mu $V/K at the Au thickness of 8nm, two orders of magnitude smaller than that in Pt/YIG. Spin-polarized density-functional calculations also show a sizable Pt but a negligible Au magnetic moment in contact with YIG, in agreement with experiments.