Theory of Huge Thermoelectric Effect Based on Magnon Drag Mechanism: Application to Thin-Film Heusler Alloy

TL;DR

This paper develops a theoretical model explaining the high thermoelectric performance of thin-film Heusler alloys through magnon drag effects linked to tungsten impurity bands, aligning well with experimental observations.

Contribution

It introduces a new theoretical framework for magnon drag in Heusler alloys, connecting impurity bands to thermoelectric enhancement, and compares predictions with experimental data.

Findings

Magnon drag significantly contributes to thermoelectric performance.

The model accurately reproduces temperature-dependent resistivity and Seebeck coefficient.

Impurity bands from tungsten substitution are key to the observed effects.

Abstract

To understand the unexpectedly high thermoelectric performance observed in the thin-film Heusler alloy Fe$_2$V$_{0.8}$W$_{0.2}$Al, we study the magnon drag effect, generated by the tungsten based impurity band, as a possible source of this enhancement, in analogy to the phonon drag observed in FeSb$_2$. Assuming that the thin-film Heusler alloy has a conduction band integrating with the impurity band, originated by the tungsten substitution, we derive the electrical conductivity $L_{11}$ based on the self-consistent t-matrix approximation and the thermoelectric conductivity $L_{12}$ due to magnon drag, based on the linear response theory, and estimate the temperature dependent electrical resistivity, Seebeck coefficient and power factor. Finally, we compare the theoretical results with the experimental results of the thin-film Heusler alloy to show that the origin of the exceptional thermoelectric properties is likely to be due to the magnon drag related with the tungsten-based impurity band.