An unconventional approach to enhance the transverse thermopower by combining magnetic and thermoelectric materials, namely the Seebeck-driven transverse thermoelectric generation (STTG), has been proposed and demonstrated recently. Here, we improve on the previously used sample structure and achieve large transverse thermopower over 40 μV K −1 due to STTG in on-chip devices. We deposited polycrystalline Fe-Ga alloy films directly on n-type Si substrates, where Fe-Ga and Si serve as the magnetic and thermoelectric materials, respectively. Using microfabrication, contact holes were created through the SiOx layer at the top of Si to electrically connect the Fe-Ga film with the Si substrate. These thin devices with simple structure clearly exhibited enhancement of transverse thermopower due to STTG, and the obtained values agreed well with the estimation over a wide range of the size ratio between the Fe-Ga film and the Si substrate.

Weyl semimetals are characterized by the presence of massless band dispersion in momentum space. When a Weyl semimetal meets magnetism, large anomalous transport properties emerge as a consequence of its topological nature. Here, using in−situ spin- and angle-resolved photoelectron spectroscopy combined with ab initio calculations, we visualize the spin-polarized Weyl cone and flat-band surface states of ferromagnetic Co2MnGa films with full remanent magnetization. We demonstrate that the anomalous Hall and Nernst conductivities systematically grow when the magnetization-induced massive Weyl cone at a Lifshitz quantum critical point approaches the Fermi energy, until a high anomalous Nernst thermopower of  ~6.2 μVK−1 is realized at room temperature. Given this topological quantum state and full remanent magnetization, Co2MnGa films are promising for realizing high efficiency heat flux and magnetic field sensing devices operable at room temperature and zero-field.

We performed a numerical analysis of the material parameters required for realizing a heat flux sensor exploiting the anomalous Nernst effect (ANE). The results showed the importance of high thermopower of ANE (S ANE ) and small saturation magnetization. This motivated us to investigate the effect of Al substitution of Fe on ANE and found S ANE = 3.4 µV/K in Fe 81 Al 19 because of the dominant intrinsic mechanism. Using this material, we made a prototype ANE-based heat flux sensor on a thin flexible polyimide sheet and demonstrated accurate sensing with it. This study gives important information for enhancing sensor sensitivity.A heat flux sensor that enables a quick detection of the magnitude and direction of heat flow is expected to be a crucial component of a smart thermal management system. However, commercially available heat flux sensors using the Seebeck effect (SE) have limitations hampering wider application. SE-based heat flux sensors use a serially connected matrix of thermocouples on a solid substrate or thick flexible sheet as a support. 1, 2) As a result, the sensor usually has a large thermal resistance that disturbs the innate heat flow. Its flexibility is also limited by its mechanical fragility. As well, although the sensitivity is proportional to the sensor's size, the complex structure makes it difficult to enlarge. To overcome these limitations, a flexible heat flux sensor based on a combination of the spin-Seebeck effect (SSE) 3,4) and the inverse spin Hall effect (ISHE) 5) has been proposed. 6) The electric field in this design is perpendicular to the direction of heat flow, in contrast to the parallel relationship in the SE design. Hence, a simple bilayer consisting of a metallic layer and a magnetic layer on a flexible sheet can detect heat flow without any patterning. This design has been demonstrated in a ferrite Ni 0.2 Zn 0.3 Fe 2.5 O 4 /Pt bilayer on a 25-µm-thick polyimide sheet. However, the sensitivity was only 0.98 nV/(W·m −2 ), about four orders of magnitude smaller that of an SE-based heat flux sensor. For practical use, the sensitivity should be improved. One way to do so is to introduce a thermopile structure with laterally connected thermocouples consisting *

The transverse thermoelectric effect refers to the conversion of a temperature gradient into a transverse charge current, or vice versa, which appears in a conductor under a magnetic field or in a magnetic material with spontaneous magnetization. Among such phenomena, the anomalous Nernst effect in magnetic materials has been receiving increased attention from the viewpoints of fundamental physics and thermoelectric applications owing to the rapid development of spin caloritronics and topological materials science. In this research trend, a conceptually different transverse thermoelectric conversion phenomenon appearing in thermoelectric/magnetic hybrid materials has been demonstrated, enabling the generation of a large transverse thermopower. Here, we review the recent progress in fundamental and applied studies on the transverse thermoelectric generation using magnetic materials.

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