Structural heterogeneity-induced enhancement of transverse magneto-thermoelectric conversion revealed by thermoelectric imaging in functionally graded materials

TL;DR

This study demonstrates that structural heterogeneity in functionally graded materials enhances transverse magneto-thermoelectric effects, revealed through high-resolution thermoelectric imaging, and offers new insights into designing advanced thermoelectric devices.

Contribution

The paper introduces a novel fabrication method for FGMs with graded heterogeneity and employs thermoelectric imaging to reveal enhanced transverse effects due to subtle structural variations.

Findings

Maximum Ettingshausen effect occurs in the atomic-heterogeneity regime

Transverse thermoelectric phenomena are highly sensitive to structural heterogeneity

Heterogeneity is confirmed by advanced microscopy techniques

Abstract

Functionally graded materials (FGMs) exhibit continuous property variations that enable unique functionalities and provide efficient platforms for systematic property optimization. Here, we report the fabrication of FGMs with graded structural heterogeneity by annealing an amorphous metal under a one-dimensional temperature gradient. Using lock-in thermography (LIT), we spatially mapped transverse thermoelectric conversion with high spatial and temperature resolution. A pronounced non-monotonic response was observed, with the maximum anomalous Ettingshausen effect, transverse charge-to-heat conversion in magnetic materials, appearing in the atomic-heterogeneity regime well before crystallization. This enhancement was not captured by conventional structural or longitudinal transport measurements, highlighting the exceptional sensitivity of transverse thermoelectric phenomena to subtle structural heterogeneity. Structural analyses using scanning transmission electron microscopy and atom probe tomography revealed Fe-based crystalline alloys and Cu nanoclusters embedded in the amorphous matrix, whose heterogeneity accounts for the enhanced response. These findings establish temperature-gradient-annealed FGMs, combined with LIT, as a powerful methodology for probing structural-heterogeneity-driven transverse electron transport and designing high-performance flexible materials.