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

Koichi Oyanagi ORCID ; Hossein Sepehri-Amin SAMURAI ORCID ; Kenta Takamori ; Terumasa Tadano SAMURAI ORCID ; Takumi Imamura ; Ren Nagasawa ; Krishnan Mahalingam ORCID ; Takamasa Hirai SAMURAI ORCID ; Fuyuki Ando SAMURAI ORCID ; Yuya Sakuraba SAMURAI ORCID ; Satoru Kobayashi ORCID ; Ken-ichi Uchida SAMURAI ORCID

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Koichi Oyanagi, Hossein Sepehri-Amin, Kenta Takamori, Terumasa Tadano, Takumi Imamura, Ren Nagasawa, Krishnan Mahalingam, Takamasa Hirai, Fuyuki Ando, Yuya Sakuraba, Satoru Kobayashi, Ken-ichi Uchida. Simultaneous achievement of large anomalous Nernst effect and reduced thermal conductivity in sintered polycrystalline topological Heusler ferromagnets. Acta Materialia. 2025, 296 (), 121239. https://doi.org/10.1016/j.actamat.2025.121239

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(abstract)

Thermoelectric conversion based on the anomalous Nernst effect (ANE) is promising for energy harvesting as its transverse geometry enables the design of large-scale thermoelectric devices with simple structures. While topological ferromagnets, typically single crystals, exhibit large ANE, achieving high conversion performance remains challenging because it also requires high electric conductivity and low thermal conductivity. Here, we report enhanced transverse thermoelectric conversion performance in polycrystalline topological ferromagnet Co2MnGa (CMG) prepared by spark plasma sintering. Optimization of the sintering conditions for CMG leads to the anomalous Nernst coefficient of 7.5 µV K-1 at room temperature, comparable to the highest value reported for the single crystals, and simultaneously reduces its thermal conductivity by 34 % compared to that of the single crystals without affecting the electric conductivity. Owing to the transport properties that overcome conventional trade-off relations, our optimized CMG slab shows the record-high value of the dimensionless figure of merit for ANE at room temperature. Detailed nano/microstructure characterizations and first-principles phonon calculations clarify the unconventional dependence of the transport properties on the degree of crystalline ordering and morphology of crystal-domain boundaries. The results reveal the potential of polycrystalline topological materials for transverse thermoelectric applications and suggest alternative strategies to nanostructuring for enhancing thermoelectric performance.

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Keyword: Anomalous Nernst effect, Heusler alloy, Microstructure characterization, Thermoelectric materials, First-principles phonon calculation

Date published: 2025-06-09

Publisher: Elsevier BV

Journal:

  • Acta Materialia (ISSN: 13596454) vol. 296 121239

Funding:

  • Japan Science and Technology Agency JPMJCR17I1
  • Japan Science and Technology Agency JPMJER2201
  • National Institute for Materials Science
  • NEC Corporation
  • Japan Society for the Promotion of Science 21K14519
  • Japan Society for the Promotion of Science 22H04965

Manuscript type: Author's version (Accepted manuscript)

MDR DOI:

First published URL: https://doi.org/10.1016/j.actamat.2025.121239

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Updated at: 2025-06-24 12:30:20 +0900

Published on MDR: 2025-06-24 12:21:27 +0900

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