Interface-induced enhancement of the anomalous Nernst effect in ferromagnetic Mn₅Ge₃C_(0.8) films

The anomalous Nernst effect of thin bilayers comprising a thin normal metal film and a ferromagnetic Mn$_5$Ge$_3$C$_{0.8}$ film has been investigated. Epitaxial c-axis grown Mn$_5$Ge$_3$C$_{0.8}$ films have been obtained by e-beam evaporation as well as by magnetron sputtering on Ge(111) substrates. The size of the anomalous Nernst coefficient is independent of the growth method. Pt, Ta, and Pt/Cu bilayers have been used as voltage leads on top of the ferromagnetic film. We show that the interface between the normal metal electrode and the ferromagnetic film contributes significantly to the anomalous Nernst voltage which is suprisingly independent of the choice of the metal. The interface-induced enhancement of the anomalous Nernst effect is verified for samples with varying Mn content or undergoing an additional annealing step. The results suggest that the interface quality has a strong impact on the size of the anomalous Nernst effect.