Page 217 - Read Online

Kautsar et al. Energy Mater. 2025, 5, 500129 Energy Materials
DOI: 10.20517/energymater.2025.26

Article Open Access

Impact of intergranular phase variations on the
anomalous Nernst effect in Nd-Fe-B permanent

magnets

2
2
1,2
Zulfa Hilmi Kautsar , Babu Madavali , Takamasa Hirai , Ken-ichi Uchida 1,2,3 , Hossein Sepehri-Amin 1,2,*
1
Graduate School of Science and Technology, University of Tsukuba, Tsukuba 305-8577, Japan.
2
National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan.
3
Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561,
Japan.
* Correspondence to: Prof. Hossein Sepehri-Amin, Research Center for Magnetic and Spintronic Materials, National Institute
for Materials Science (NIMS), Sengen 1-2-1, Tsukuba 305-0047, Japan. E-mail: h.sepehriamin@nims.go.jp
How to cite this article: Kautsar, Z. H.; Madavali, B.; Hirai, T.; Uchida, K.; Sepehri-Amin, H. Impact of intergranular phase
variations on the anomalous Nernst effect in Nd-Fe-B permanent magnets. Energy Mater. 2025, 5, 500129. https://dx.doi.org/10.
20517/energymater.2025.26

Received: 29 Jan 2025 First Decision: 18 Mar 2025 Revised: 18 Apr 2025 Accepted: 30 Apr 2025 Published: 26 Jun 2025
Academic Editor: Sining Yun Copy Editor: Ping Zhang Production Editor: Ping Zhang

Abstract
Improving the anomalous Nernst coefficient (S ANE ) in permanent magnets is essential for increasing the
power density in transverse thermoelectric generators, which use permanent magnets to operate the anomalous
Nernst effect without relying on an external magnetic field. While recent studies indicate that microstructural
engineering can affect S , the specific relationship between microstructure and S ANE in permanent magnets
ANE
remains underexplored. This study investigates S ANE of hot-pressed, hot-deformed, and RE-Cu (RE = Dy-Nd, Nd,
and Pr) grain boundary diffusion-processed Nd-Fe-B magnets. The results show that S ANE increases by 68%, from
-1
-7
-1
-7
-2.6 × 10 VK in the hot-pressed state to -4.4 × 10 VK after hot-deformation in which grain growth and
crystallographic texture are realized without changing the composition of the magnets. S ANE further increases to
-7
-1
-5.0 × 10 VK after grain boundary structure and composition change from thin amorphous phase to thick
crystalline phase by grain boundary diffusion of Dy-Nd-Cu alloy. The increase in S ANE is found to be primarily due to
the reduction of the opposing transverse electric field caused by the Seebeck-effect-induced carrier flow bent by
the anomalous Hall effect. Owing to the crystallographic texture formation after hot-deformation, almost the same
transverse thermopower as S ANE is obtained in the hot-deformed and RE-Cu grain boundary diffusion-processed
Nd-Fe-B magnets at a remanence state, i.e., under zero magnetic field. These findings demonstrate that
microstructural optimization can effectively enhance the S ANE in ultra-fine grained Nd-Fe-B magnets, providing a
promising avenue for advancing materials in applications of transverse thermoelectrics.

Keywords: Anomalous Nernst effect, hot-deformed magnets, microstructural engineering, Nd-Fe-B, permanent
magnets

© The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution 4.0
International License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, sharing,
adaptation, distribution and reproduction in any medium or format, for any purpose, even commercially, as
long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and
indicate if changes were made.

www.oaepublish.com/energymater