Large anomalous Nernst and spin Nernst effects in noncollinear antiferromagnets Mn$_3X$ ($X$ = Sn, Ge, Ga)

TL;DR

This study reveals that noncollinear antiferromagnets Mn$_3X$ exhibit large anomalous Nernst and spin Nernst effects, surpassing some ferromagnets and metals, with potential applications in thermoelectronic and spin caloritronic devices.

Contribution

The paper provides first-principles calculations showing large anomalous Nernst and spin Nernst effects in Mn$_3X$ antiferromagnets, highlighting their potential for spintronics and thermoelectric applications.

Findings

Large anomalous Nernst conductivity in Mn$_3X$ alloys, up to 5 times that of iron.

Significant spin Nernst conductivity in Mn$_3$Sn and Mn$_3$Ga, comparable to platinum.

Good agreement of calculated properties with recent experimental data.

Abstract

Noncollinear antiferromagnets have recently been attracting considerable interest partly due to recent surprising discoveries of the anomalous Hall effect (AHE) in them and partly because they have promising applications in antiferromagnetic spintronics. Here we study the anomalous Nernst effect (ANE), a phenomenon having the same origin as the AHE, and also the spin Nernst effect (SNE) as well as AHE and the spin Hall effect (SHE) in noncollinear antiferromagnetic Mn$_3X$ ($X$ = Sn, Ge, Ga) within the Berry phase formalism based on {\it ab initio} relativistic band structure calculations. For comparison, we also calculate the anomalous Nernst conductivity (ANC) and anomalous Hall conductivity (AHC) of ferromagnetic iron as well as the spin Nernst conductivity (SNC) of platinum metal. Remarkably, the calculated ANC at room temperature (300 K) for all three alloys is huge, being up to 5 times larger than that of iron. Moreover, the calculated SNC for Mn$_3$Sn and Mn$_3$Ga is also large, being as large as that of platinum. This suggests that these anitferromagnets would be useful materials for thermoelectronic devices and spin caloritronic devices. The calculated ANC of Mn$_3$Sn and iron are in reasonably good agreement with the very recent experiments. The calculated SNC of platinum also agrees with the very recent experiments in both sign and magnitude. The calculated thermoelectric and thermomagnetic properties are analyzed in terms of the band structures as well as the energy-dependent AHC, ANC, SNC and spin Hall conductivity via the Mott relations.