Anomalous Hall and Nernst effects in ferrimagnetic Mn${}_4$N films: possible interpretation and prospect for enhancement

Abstract

Ferrimagnetic Mn${}_4$N is a promising material for heat flux sensors based on the anomalous Nernst effect (ANE) because of its sizable uniaxial magnetic anisotropy ($K_{\mathrm{u}}$) and low saturation magnetization ($M_{\mathrm{s}}$). We experimentally and theoretically investigated the ANE and anomalous Hall effect in sputter-deposited Mn${}_4$N films. It was revealed that the observed negative anomalous Hall conductivity (${\sigma }_{xy}$) could be explained by two different coexisting magnetic structures, that is, a dominant magnetic structure with high $K_{\mathrm{u}}$ contaminated by another structure with negligible $K_{\mathrm{u}}$ owing to an imperfect degree of order of nitrogen. The observed transverse thermoelectric power ($S_{\mathrm{ANE}}$) of $+0.5\mu V/K$ at $300\mathrm{K}$ gave a transverse thermoelectric coefficient (${\alpha }_{xy}$) of $+0.34A/(\mathrm{m}\cdot \mathrm{K})$, which was smaller than the value predicted from first-principles calculation. The interpretation for ${\alpha }_{xy}$ based on the first-principles calculations led us to conclude that the realization of single magnetic structure with high $K_{\mathrm{u}}$ and optimal adjustment of the Fermi level are promising approaches to enhance $S_{\mathrm{ANE}}$ in Mn${}_4$N through the sign reversal of ${\sigma }_{xy}$ and the enlargement of ${\alpha }_{xy}$ up to a theoretical value of $1.77A/(\mathrm{m}\cdot \mathrm{K})$.

28 pages, 6 figures, 1 table (including supplemental material)