Measurements of spin polarization of epitaxial SrRuO3 thin films

We have measured the transport spin polarization of epitaxial thin films of the conductive ferromagnetic oxide, SrRuO3, using point contact Andreev reflection spectroscopy. In spite of the fact that spin-up and spin-down electronic densities of states at the Fermi level for SrRuO3 calculated from band structure theory are practically the same, the experimental transport spin polarization for these films was found to be about 50%. This is a direct consequence of the Fermi velocity disparity between the majority and minority bands. The experimental results are compared with our theoretical estimates of the spin polarization in the ballistic and diffusive limits.