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arXiv · 2401.11692

Quantitative measurement of figure of merit for transverse thermoelectric conversion in Fe/Pt metallic multilayers

Takumi Yamazaki·Takamasa Hirai·Takashi Yagi·Yuichiro Yamashita·Ken-ichi Uchida·Takeshi Seki·Koki Takanashi
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Abstract

This study presents a measurement method for determining the figure of merit for transverse thermoelectric conversion ($ z_\mathrm{T}T $) in thin film forms. Leveraging the proposed methodology, we comprehensively investigate the transverse thermoelectric coefficient ($ S_\mathrm{T} $), in-plane electrical conductivity ($ σ_{yy} $), and out-of-plane thermal conductivity ($ κ_{xx} $) in epitaxial and polycrystalline Fe/Pt metallic multilayers. The $ κ_{xx} $ 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 $ κ_{xx} $. $ z_\mathrm{T}T $ is found to increase with increasing $ N $, which remarkably reflects the $ N $-dependent enhancement of the $ S_\mathrm{T} $ values. Notably, $ S_\mathrm{T} $ and $ σ_{yy} $ are significantly larger in the epitaxial multilayers than those in the polycrystalline counterparts, whereas negligible differences in $ κ_{xx} $ are observed between the epitaxial and polycrystalline multilayers. This discrepancy in $ σ_{yy} $ and $ κ_{xx} $ 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 $ z_\mathrm{T}T $ in the multilayers. This study is the first demonstration in the evaluation of $ z_\mathrm{T}T $ in thin film forms, and our proposed measurement technique reveals the transverse thermoelectric properties inherent to multilayers.

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Takumi Yamazaki, Takamasa Hirai, Takashi Yagi, Yuichiro Yamashita, Ken-ichi Uchida, Takeshi Seki, Koki Takanashi. 2024-01-22. Quantitative measurement of figure of merit for transverse thermoelectric conversion in Fe/Pt metallic multilayers. https://arxiv.org/abs/2401.11692

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