Magneto-thermoelectric measurements on epitaxial Heusler alloy thin films*

Full Heusler compounds with the composition Co₂Mn(Al,Si) are of interest due to their nearly half-metallic behavior. We have measured the Seebeck and anomalous Nernst coefficients in epitaxial MgO(001)/Co₂MnAl_xS_1-x thin films using a novel all-electrical device fabricated through straightforward top-down photolithography techniques. Because the scattering rate cancels out in expressions for the thermoelectric coefficients (to first approximation), they can provide more direct information about the electronic structure than is accessible using only ordinary magneto-transport. Among our samples, we found Co₂MnAl to have the largest anomalous Nernst coefficient of -4 Am^-1K^-1 at room temperature, which is larger than the value of -2 Am^-1K^-1measured in bulk polycrystalline Fe [S. J. Watzman et al., Phys. Rev. B 94, 144407 (2016)] . We discuss how these measurements can be applied as a probe of a material’s spin polarization, so that they can be used as a tool for optimizing magneto-electronic properties of quaternary Heusler alloys.