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This study presents a measurement method for determining the figure of merit for transverse thermoelectric conversion (zT) in thin film forms. Leveraging the proposed methodology, we comprehensively investigate the transverse thermoelectric coefficient (S), in-plane electrical conductivity (σ), and out-of-plane thermal conductivity (κ) in epitaxial and polycrystalline Fe/Pt metallic multilayers. The κ values of multilayers with a number of stacking repetitions (N) of 200 are lower than those of FePt alloy films, indicating that the multilayer structure effectively contributes to the suppression of κxx. zT is found to increase with increasing N, which remarkably reflects the N-dependent enhancement of the ST values. Notably, S and σ are significantly larger in the epitaxial multilayers than those in the polycrystalline counterparts, whereas negligible differences in κ are observed between the epitaxial and polycrystalline multilayers. This discrepancy in σ and κ with respect to crystal growth is due to the different degree of anisotropy in electron transport between epitaxial and polycrystalline multilayers, and epitaxial growth can lead to an enhancement of zT in the multilayers. This study is the first demonstration in the evaluation of zT in thin film forms, and our proposed measurement technique reveals the transverse thermoelectric properties inherent to multilayers.

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Keyword: anomalous Nernst effect, dimensionless figure of merit, spin caloritronics, time-domain thermoreflectance

Date published: 2024-02-21

Publisher: American Physical Society (APS)

Journal:

• Physical Review Applied (ISSN: 23317019) vol. 21 issue. 2 024039

Funding:

• JSPS JP18H05246 (Grant-in-Aid for Scientific Research (S) )
• JSPS JP22H04965 (Grant-in-Aid for Scientific Research (S) )
• JSPS JP22K20495 (Grant-in-Aid for Research Activity Start-up)
• JST JPMJCR17I1 (CREST "Creation of Innovative Core Technologies for Nano-enabled Thermal Management")
• JST JPMJER2201 (ERATO "Magnetic Thermal Management Materials")
• JSPS JP22KJ0210 (Research Fellowship for Young Scientists)

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.4409

First published URL: https://doi.org/10.1103/physrevapplied.21.024039

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Updated at: 2024-02-26 12:30:27 +0900

Published on MDR: 2024-02-26 12:30:27 +0900