Magnon scattering in the transport coefficients of CoFe thin films

Abstract

Resistivity $\ensuremath{\rho}$, thermopower $\mathcal{S}$, and thermal conductivity $\ensuremath{\kappa}$ were measured simultaneously on a set of CoFe alloy films. Variation of the Co content ${x}_{\mathrm{Co}}$ allows for a systematic tuning of the Fermi level through the band structure, and the study of the interplay between electronic and magnetic contributions to the transport coefficients. While band-structure and magnon effects in $\ensuremath{\rho}$ and $\ensuremath{\kappa}$ are rather weak, they turn out to be very significant in $\mathcal{S}$. A decomposition of $\mathcal{S}$ into Mott and magnon drag contributions results in a systematic evolution between the two limiting cases of pure Fe and pure Co. At low temperatures, we find an interesting sign change of the curvature of $\mathcal{S}(T)$ that indicates a corresponding sign change of the magnon drag.