Weinan ZHOUFig. 1. Difference between SE in thermoelectric materials and ANE in magnetic materials, as well as the corresponding designs of heat flux sensors. The photograph is a prototype ANE-based heat flux sensor, fabricated on a flexible polyimide sheet.Fig. 2. Schematic illustration of combing magnetic and thermoelectric materials for transverse thermoelectric generation, as well as the results of total transverse thermopower as a function of layer thickness ratio.References 1) K. Uchida, W. Zhou and Y. Sakuraba, Appl. Phys. Lett. 118, 140504 (2021). 2) W. Zhou and Y. Sakuraba, Appl. Phys. Express 13, 043001 (2020). 3) W. Zhou, K. Yamamoto, A. Miura, R. Iguchi, Y. Miura, K. Uchida, and Y. Sakuraba, Nat. Mater. 20, 463 (2021). 4) W. Zhou, T. Sasaki, K. Uchida, and Y. Sakuraba, Adv. Sci. 11, 2308543 (2024).thermopower, which varies with changing layer thicknesses (magnetic layer: tM; thermoelectric layer: tTE; bilayer: ttot) and peaks at a much larger value under an optimal thickness ratio [Fig. 2]. We reproduced this behavior in the experiment. We measured the transport properties of a serial of samples, which are prepared by depositing Fe-Ga alloy thin films of various thicknesses onto n-type Si substrates. The predicted tendency of transverse thermopower is nicely reproduced by the measured results [Fig. 2]. The value obtained from the sample with optimized layered structures reaches 15.2±0.4 μV K−1 [4], which is a fivefold increase from that of Fe-Ga alloy and much larger than the current room temperature record observed in Weyl semimetal Co2MnGa. These findings highlight the potential in combining magnetic and thermoelectric materials for transverse thermoelectric applications.1. Outline of ResearchTransverse thermoelectric generation converts temperature gradient (∇T) in one direction into electric field (E) perpendicular to that direction. The anomalous Nernst effect (ANE) observed in magnetic materials is a well-known example. This orthogonal relationship between ∇T and E allows the thermoelectric module to have a simple 2D structure made of connecting wires on a surface instead of a complicated 3D structure [Fig. 1]. This is beneficial for achieving better flexibility and scalability while avoiding challenging problems thermoelectric modules including heat flux sensors, which are based on the Seebeck effect (SE) [1,2]. However, the transverse thermopower of ANE is still small compared to the longitudinal thermopower thermoelectric materials. Recently, significant of SE of enhancement of transverse thermopower is observed in closed circuits consisting of magnetic and thermoelectric materials, referred transverse magneto-thermoelectric generation (STTG). The SE of thermoelectric material generates a large longitudinal charge current in the magnetic material, which is then converted to the transverse direction by its anomalous Hall effect, leading to a giant transverse thermopower [3]. However, forming of a closed circuit requires electrical connection only at the two ends along the direction of ∇T but insulation in between, which could be a challenge for device fabrication and hinder its wide adoption.2. Research ActivitiesWe achieved STTG in the simplest way to combine magnetic and thermoelectric materials, namely, by stacking a magnetic layer and a thermoelectric layer together to form a bilayer. Different from the closed circuit, the magnetic and thermoelectric layers are in direct electrical contact over the entire interface. We model this bilayer and derive the expression for its transverse the Seebeck-driven to as that faces ICYS Annual Report 2023 Research Digest 31Transverse Thermoelectric Generation for Heat FluxSensing
元のページ ../index.html#33