Anomalous Hall and Nernst effects in ferrimagnetic Mn4N films: Possible interpretations and prospects for enhancement

Ferrimagnetic Mn4N is a promising material for heat flux sensors, based on the anomalous Nernst effect (ANE), because of its sizeable uniaxial magnetic anisotropy (Ku) and low saturation magnetization (Ms). We experimentally and theoretically investigated the ANE and anomalous Hall effect in sputter-deposited Mn4N films. It was revealed that the observed negative anomalous Hall conductivity (σxy) could be explained by two different coexisting magnetic structures, that is, a dominant magnetic structure with high Ku, contaminated by another structure with negligible Ku, owing to an imperfect degree of order of N. The observed transverse thermoelectric power (SANE) of +0.5 μV/K at 300 K yielded a transverse thermoelectric coefficient (αxy) of +0.34 A/(m  · K), which was smaller than the value predicted from the first-principles calculation. The interpretation for αxy based on the first-principles calculations led us to conclude that the realization of single magnetic structure with high Ku and optimal adjustment of the Fermi level are promising approaches to enhance SANE in Mn4N through the sign reversal of σxy and the enlargement of αxy up to a theoretical value of 1.77 A/(m  · K).