The recently discovered spin Seebeck effect (SSE) which generates spin voltage due to a temperature gradient in ferromagnets, was systematically studied in half-metallic Heusler compound ${\mathrm{Co}}_2\mathrm{MnSi}$ (CMS)/Pt thin films to investigate the effect of spin polarization of ferromagnetic layer on SSE. An epitaxial thin film of CMS with an almost perfect $B$2-ordered structure was prepared directly on a MgO(001) substrate. The measurement was performed at room temperature for various temperature differences, Δ$T$ $=$ 0–20 K between higher (300 K$+$Δ$T$) and lower (300 K) temperature ends along the film. The clear sign reversal of the thermally induced spin voltage due to SSE at the higher and lower temperature ends of the CMS film was detected by means of inverse spin-Hall effect in a Pt wire. The SSE was also investigated in a Py thin film deposited on a MgO(001) substrate and compared to that with CMS to verify the effect of spin polarization on SSE. Comparable signals of SSE in CMS and Py thin films suggested that thermal excitation of magnons might have more vital effects in SSE than the degree of spin polarization in ferromagnetic metals.

• Received 19 November 2010

DOI:https://doi.org/10.1103/PhysRevB.83.224401