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

This study presents a measurement method for determining the figure of merit for transverse thermoelectric conversion (zTT) in thin-film forms. Leveraging the proposed methodology, we comprehensively investigate the transverse thermoelectric coefficient (ST), in-plane electrical conductivity (sigma yy), and outof-plane thermal conductivity (kappa xx) in epitaxial and polycrystalline Fe/Pt metallic multilayers. Multilayers with a number of stacking repetitions (N) of 200 have kappa xx values that are lower than those of FePt alloy films, indicating that the multilayer structure effectively contributes to the suppression of kappa xx. zTT is found to increase with increasing N, which remarkably reflects the N-dependent enhancement of the ST values. Notably, ST and sigma yy are significantly larger in the epitaxial multilayers than in the polycrystalline counterparts, whereas negligible differences in kappa xxare observed between the epitaxial and polycrystalline multilayers. The present measurement technique reveals the transverse thermoelectric properties inherent to multilayers.