Graded magnetic materials offer new avenues for thermoelectric applications

A research team from NIMS and the University of Tokyo has proposed that by developing an artificial material in which multilayers of magnetic metal and semiconductor are laminated alternately and diagonally, transverse magneto-thermoelectric conversion in magnetic materials can be utilized with higher performance than previously possible. And it was proven.

The study is published in the journal Nature Communications.

When a temperature gradient is applied to a magnetic conductor, a charging current is generated in a direction perpendicular to both the temperature gradient and the magnetization direction of the magnetic conductor.

This transverse magnetic thermoelectric phenomenon, known as the anomalous Nernst effect (ANE), has attracted great interest as a potential for versatile, durable, and low-cost thermoelectric applications. Currently, with the aim of further improving the performance of ANE, the search for new magnetic materials focusing on the topological properties of the material is actively underway.

Despite these efforts, no material has yet been identified with room temperature performance in ANE that exceeds that of cobalt-based topological magnets, namely CoMnGa, reported in 2018, limiting further progress in this field. There is. Moreover, even the current record performance of Co2MnGa needs to be improved by about 100 times or more for practical thermoelectric applications.

A research team recently developed an artificially graded multilayer consisting of alternating layers of magnetic metal and semiconductor that simultaneously exhibits both the off-diagonal Seebeck effect (ODSE) and ANE. Here, ODSE realizes the lateral thermoelectric conversion resulting from the tilted multilayer structure without the need for external magnetic fields or magnetization.

The research team demonstrated that the synergy between ANE and ODSE improves the dimensionless figure of merit of ANE in engineered materials by more than an order of magnitude compared to the same single magnetic metal alone.

These findings indicate that factors such as specific physical parameters and structure, which have not been the focus of previous studies on ANEs, are important for improving the performance of lateral thermoelectric conversion.

This research provides new guidelines for the new material design of horizontal thermoelectric conversion materials based on structural design and new ways to utilize ANE from a completely different perspective from previous research.

Based on these guidelines, the research team aims to develop artificial materials with high thermoelectric performance for practical applications such as power generation using waste heat, electronic cooling, and thermal sensing technology.