Tilted magnetic materials offer fresh path for thermoelectric applications

A research team from NIMS and UTokyo has proposed and demonstrated that the transverse magneto-thermoelectric conversion in magnetic materials can be utilized with much higher performance than previously by developing artificial materials comprising alternately and obliquely stacked multilayers of a magnetic metal and semiconductor.

The work is published in the journal Nature Communications.

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

This transverse magneto-thermoelectric phenomenon, known as the anomalous Nernst effect (ANE), has attracted considerable interest for potentially versatile, durable, and low-cost thermoelectric applications. Currently, the search for new magnetic materials focusing on topological natures of materials is being actively pursued with the aim of further improving the performance of ANE.

Despite these efforts, no material has yet been identified with the performance of ANE at room temperature exceeding that of a cobalt-based topological magnet, i.e., Co₂MnGa, reported in 2018, limiting further progress in this field. In addition, even this current record-high performance of Co₂MnGa would have to be improved around more than 100 times for practical thermoelectric applications.

The research team recently developed an artificially tilted multilayer composed of alternating layers of a magnetic metal and semiconductor to simultaneously exhibit both the off-diagonal Seebeck effect (ODSE) and ANE. Here, ODSE realizes the transverse thermoelectric conversion arising from tilted multilayer structures without the need for external magnetic fields or magnetization.

The team demonstrated that the dimensionless figure of merit for ANE in the artificial material was improved by more than one order, compared to that of the same single magnetic metal alone, owing to the synergetic action of ANE and ODSE.

These findings indicate that factors, such as certain physical parameters and structures, which have not been the focus of previous studies on ANE, are important for improving the performance of transverse thermoelectric conversion.

The research provides new guidelines for the design of new materials for transverse thermoelectric conversion materials based on structural design, as well as new ways of utilizing ANE, from a completely different perspective from the 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 and electronic cooling and heat sensing technologies.

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