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Bipolarity of large anomalous Nernst effect in Weyl magnet-based alloy films

Nature Physics volume 20, pages 254–260 (2024)Cite this article

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Abstract

A thermopile device converts thermal energy to electrical energy. Controlling the polarity of the thermoelectric voltage that such a device generates is an important part of enhancing its thermoelectric output. Constructing thermopile devices where the mechanism is based on the anomalous Nernst effect in topological magnets and where one can control the bipolarity is still hard to do. Here we demonstrate the bipolarity of a large anomalous Nernst effect in a series of Weyl ferromagnet Co3Sn2S2-based alloy films by tuning the Fermi energy. We illustrate the bipolarity of the anomalous Nernst signal originating from the intrinsic Berry curvature contribution by systematically regulating the Fermi energy by nickel or indium substitution while maintaining a topological band feature of the Weyl ferromagnet. The bipolarity enables the construction of the Weyl magnet-based anomalous Nernst thermopile that generates large thermoelectric output at zero magnetic field. These demonstrations of bipolar large anomalous Nernst effect in Co3Sn2S2-based films will stimulate the device development of efficient thermoelectric energy conversion exploiting topological magnets.

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Fig. 1: Polarity of Seebeck effect and anomalous Nernst effect.
Fig. 2: Concept and experimental verification of Weyl feature in Co3Sn2S2 film.
Fig. 3: Bipolar large anomalous Nernst effect.
Fig. 4: Correlations of key parameters, SANE and Bc, guiding for stable device operation based on ANE under in-plane thermal gradient and zero magnetic field.
Fig. 5: Demonstration of zero-field thermopile operation based on Weyl magnet Co3Sn2S2-based alloy films.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Code availability

Computer codes used in this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank S. Nishimura and J. Shiogai for fruitful discussion about the measurement setup for magneto-thermoelectric properties and the NEOARK Corporation for the use of a maskless lithography system PALET. This work was supported by JSPS KAKENHI (Grant Nos. 22H00288, A.T.; 21H01789, M.-T.S.; 21H04437, M.-T.S.; 19H01842, M.-T.S.; 20K05299, Y.Y.; and 21H01031, Y.Y.), JST ERATO (Grant No. JPMJER2201, K.U.) and JST CREST (Grant No. JPMJCR18T2, A.T.).

Author information

Author notes

  1. These authors contributed equally: Shun Noguchi, Kohei Fujiwara.

Authors and Affiliations

  1. Institute for Materials Research, Tohoku University, Sendai, Japan

    Shun Noguchi, Kohei Fujiwara, Michi-To Suzuki, Takeshi Seki, Ken-ichi Uchida & Atsushi Tsukazaki

  2. Center for Liberal Arts and Sciences, Faculty of Engineering, Toyama Prefectural University, Imizu, Japan

    Yuki Yanagi

  3. Center for Spintronics Research Network, Graduate School of Engineering Science, Osaka University, Toyonaka, Japan

    Michi-To Suzuki

  4. Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science, Tsukuba, Japan

    Takamasa Hirai & Ken-ichi Uchida

  5. Center for Science and Innovation in Spintronics (CSIS), Core Research Cluster, Tohoku University, Sendai, Japan

    Atsushi Tsukazaki

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Contributions

K.F. grew the thin films. S.N. and K.F. prepared the sample for thermoelectric measurements. S.N. carried out the electrical and thermoelectric measurements with support from K.F. Magnetization measurement was carried out by K.F. and T.S. Calibration of the measurement setup for the Seebeck effect was carried out by T.H., K.U. and K.F. First-principle band calculation was carried out by Y.Y. and M.-T.S. S.N., K.F. and A.T. wrote the draft. All the authors discussed the results and commented on the manuscript. K.F. and A.T. conceived the project.

Corresponding author

Correspondence to Kohei Fujiwara.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–14, Table 1 and references.

Source data

Source Data Fig. 2

Energy distributions of anomalous Hall conductivity and anomalous Nernst conductivity, magnetic field dependences of magnetization and Hall conductivity at T = 150 K, and magnetic field dependences of Nernst coefficient at various temperatures.

Source Data Fig. 3

Magnetic field dependences of Hall resistivity and Nernst coefficient for various compositions and composition dependences of anomalous Hall conductivity and anomalous component of Nernst coefficient at T = 100 K.

Source Data Fig. 4

Anomalous component of Nernst coefficients in literature and this study.

Source Data Fig. 5

Magnetic field, connection number, and temperature dependences of thermoelectric voltage.

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Noguchi, S., Fujiwara, K., Yanagi, Y. et al. Bipolarity of large anomalous Nernst effect in Weyl magnet-based alloy films. Nat. Phys. 20, 254–260 (2024). https://doi.org/10.1038/s41567-023-02293-z

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