Enhancement of the anomalous Nernst effect in epitaxial Fe4N films grown on SrTiO3(001) substrates with oxygen deficient layers

Anomalous Nernst effect of epitaxial Fe4N films on MgO(001), MgAl2O4(MAO)(001), and SrTiO3(STO)(001) substrates grown by molecular beam epitaxy was investigated. Moderately large anomalous Nernst coefficients (SANE) of 1.4 and 1.7 μV/K were obtained in the Fe4N films on the MgO(001) and MAO(001) substrates, respectively, and large anomalous Hall angles (∼0.06) and transverse thermoelectric conductivities [∼1.3 A/(m K)] were derived from the experimental results. On the other hand, a large effective SANE of 2.8 μV/K was obtained in the Fe4N film on the STO(001) substrate. The origin of the enhanced effective SANE is the negatively large Seebeck coefficient (SSE) in an oxygen deficient STO layer near the surface of the STO substrate. This indicates that it is possible to enhance the effective SANE of ferromagnetic materials by utilizing adjacent materials with large |SSE| such as the oxygen deficient STO layer.