Simultaneous achievement of large anomalous Nernst effect and reduced thermal conductivity in sintered polycrystalline topological Heusler ferromagnets

TL;DR

This paper demonstrates that polycrystalline topological Heusler ferromagnets can achieve both large anomalous Nernst effects and low thermal conductivity, promising for thermoelectric applications.

Contribution

It reports the first large anomalous Nernst effect in sintered polycrystalline topological Heusler ferromagnets with optimized thermal and structural properties.

Findings

Anomalous Nernst coefficient ~7.5 μV/K at room temperature

Record-high figure of merit ~8×10^{-4} at room temperature

Transport properties depend on crystalline ordering and domain boundaries

Abstract

This study reports the observation of the large anomalous Nernst effect in polycrystalline ferromagnetic Co$_{2}$MnGa (CMG) slabs prepared by a spark plasma sintering method. By optimizing the sintering conditions, the anomalous Nernst coefficient reaches ~7.5 $\mu$V K$^{-1}$ at room temperature, comparable to the highest value reported in the single-crystalline CMG slabs. Owing to the sizable anomalous Nernst coefficient and reduced thermal conductivity, the dimensionless figure of merit in our optimized CMG slab shows the record-high value of ~8$\times$10$^{-4}$ at room temperature. With the aid of the nano/microstructure characterization and first-principles phonon calculation, this study discusses the dependence of the transport properties on the degree of crystalline ordering and morphology of crystal-domain boundaries in the sintered CMG slabs. The results reveal a potential of polycrystalline topological materials for transverse thermoelectric applications, enabling the construction of large-scale modules.