Large magnon-induced anomalous Nernst conductivity in single-crystal MnBi

Bin He; Cüneyt Şahin; Stephen R Boona; Brian C Sales; Yu Pan; Claudia Felser; Michael E Flatté; Joseph P Heremans

doi:10.1016/j.joule.2021.08.007

Large magnon-induced anomalous Nernst conductivity in single-crystal MnBi

Joule. 2021 Nov 17;5(11):3057-3067. doi: 10.1016/j.joule.2021.08.007.

Authors

Bin He^{1

2}, Cüneyt Şahin^{3

4}, Stephen R Boona⁵, Brian C Sales⁶, Yu Pan¹, Claudia Felser¹, Michael E Flatté^{3

4}, Joseph P Heremans^{2

7

8}

Affiliations

¹ Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany.
² Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA.
³ Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA.
⁴ Optical Science and Technology Center and Department of Physics and Astronomy, the University of Iowa, Iowa City, IA 52242, USA.
⁵ Center of Electron Microscopy and Analysis, The Ohio State University, Columbus, OH 43210, USA.
⁶ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
⁷ Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, USA.
⁸ Department of Physics, The Ohio State University, Columbus, OH 43210, USA.

Abstract

Thermoelectric modules are a promising approach to energy harvesting and efficient cooling. In addition to the longitudinal Seebeck effect, transverse devices utilizing the anomalous Nernst effect (ANE) have recently attracted interest. For high conversion efficiency, it is required that the material have a large ANE thermoelectric power and low electrical resistance, which lead to the conductivity of the ANE. ANE is usually explained in terms of intrinsic contributions from Berry curvature. Our observations suggest that extrinsic contributions also matter. Studying single-crystal manganese-bismuth (MnBi), we find a high ANE thermopower (∼10 μV/K) under 0.6 T at 80 K, and a transverse thermoelectric conductivity of over 40 A/Km. With insight from theoretical calculations, we attribute this large ANE predominantly to a new advective magnon contribution arising from magnon-electron spin-angular momentum transfer. We propose that introducing a large spin-orbit coupling into ferromagnetic materials may enhance the ANE through the extrinsic contribution of magnons.

Keywords: anomalous Nernst effect; ferromagnetic bismuthide; magnons; thermoelectricity.