Presentation Information
[P1-48]Development of RE2(Fe,Co)14B (RE = rare-earth) compounds for transverse thermoelectric applications
*Babu Madavali1, Fuyuki Ando1, Zulfa Hilmi Kautsar1, Takamasa Hirai1, Ken-ichi Uchida1,2, Xin Tang1, Hossein Sepehri-Amin1 (1. National Institute for Materials Science (NIMS) (Japan), 2. The University of Tokyo, Kashiwa (Japan))
Keywords:
permanent magnets,anomalous Nernst/Ettingshausen effect,transverse thermoelectrics
Development of new permanent magnets are in high demand for the use in transverse thermoelectric generation (TEG), as their strong remanent magnetization and high coercivity allow TEGs to operate without requiring an external magnetic field. Recently, TEGs based on the anomalous Nernst effect (ANE) has received much interest because of simple lateral device structures and its intriguing physical mechanisms [1-3]. Moreover, the performance of transverse thermoelectrics has improved significantly by developing a multifunctional composite magnet (MCM) using SmCo5/Bi0.2Sb1.8Te3 multilayers, with the resulting MCM thermopile module generating a maximum power of 204 mW at a temperature difference of 152 K, comparable to commercial thermoelectric modules utilizing the Seebeck effect [4]. These findings strongly motivate further exploration of new materials design and investigations into the application of permanent magnets for transverse thermoelectric conversion.
In this work, we have explored the potential of RE2Fe14B (RE=Tb, Dy, Ho, and Nd) and Nd2(Fe1-pCop)14B (p = 0 - 1) compounds and systematically investigated the transverse thermoelectric properties at room temperature. The detailed crystal structure and chemical composition analyses of the alloys showed the polycrystalline 2:14:1 as the main phases in all samples with some minor secondary phases such as α-Fe or RE-rich phases for all the samples [5]. The transverse thermoelectric signals were measured by a lock-in thermography technique with external magnetic field of ±1 T. We obtained the negative anomalous Nernst coefficient SANE for all the RE2Fe14B alloys regardless of the RE element and the highest negative SANE(14T) of -0.67×10-6 VK-1 for Tb2Fe14B among them, which is comparable to that of the commercial Nd2Fe14B sintered permanent magnets with an optimized microstructure [2]. The substitution of Co for Fe site in Nd2(Fe1-pCop)14B alloys causes sign reversal (from negative to positive) of SANE values. The transverse thermoelectric conductivity is responsible for the sign change in SANE values. As a result, the Nd2(Fe0.4Co0.6)14B alloy shows the highest positive SANE(14T) of +1.87×10-6 VK-1, revealing that the RE and 3d transition metal elements play the distinct roles on the transverse thermoelectric performance in RE2(Fe,Co)14B compounds.
Furthermore, we have developed the Nd2(Fe0.4Co0.6)14B permanent magnet to realize the high coercivity for zero field ANE device operations. The hot-pressed magnets were processed through the grain boundary diffusion process (GBDP) using Pr80Cu20 (~5wt.%) as a diffusion source for Nd2(Fe0.4Co0.6)14B alloys at optimized heat-treatment conditions. The GBDP samples had a fine grain with rare-earth (RE) rich IGP phases at grain boundaries. The formation of such non-ferromagnetic IGP reduces the intergranular exchange coupling, which results in increase in coercivity [6]. The GBDP sample shows SANE (0T) of +2.33×10-6 VK-1 measured at remanent state, which is higher than that of the ingots. These developed Nd2(Fe0.4Co0.6)14B permanent magnets excelled the promising transverse thermoelectric properties, which can be scale-up the zero field ANE power generation applications [3].
REFERENCES
[1] K. Uchida, Joule, 6 (2022) 2240–2245.
[2] A. Miura et al. Appl. Phys. Lett. 115 (2019) 222403.
[3] F. Ando, APL Energy. 2 (2024) 016103.
[4] F. Ando, Energy Environ. Sci. 2025(In press) [https://arxiv.org/abs/2402.18019].
[5] H. Sepehri-Amin et al. Acta Mater. 60 (2012) 819-830.
[6] H. Sepehri-Amin et al. Acta Mater. 99 (2015) 297-306.
In this work, we have explored the potential of RE2Fe14B (RE=Tb, Dy, Ho, and Nd) and Nd2(Fe1-pCop)14B (p = 0 - 1) compounds and systematically investigated the transverse thermoelectric properties at room temperature. The detailed crystal structure and chemical composition analyses of the alloys showed the polycrystalline 2:14:1 as the main phases in all samples with some minor secondary phases such as α-Fe or RE-rich phases for all the samples [5]. The transverse thermoelectric signals were measured by a lock-in thermography technique with external magnetic field of ±1 T. We obtained the negative anomalous Nernst coefficient SANE for all the RE2Fe14B alloys regardless of the RE element and the highest negative SANE(14T) of -0.67×10-6 VK-1 for Tb2Fe14B among them, which is comparable to that of the commercial Nd2Fe14B sintered permanent magnets with an optimized microstructure [2]. The substitution of Co for Fe site in Nd2(Fe1-pCop)14B alloys causes sign reversal (from negative to positive) of SANE values. The transverse thermoelectric conductivity is responsible for the sign change in SANE values. As a result, the Nd2(Fe0.4Co0.6)14B alloy shows the highest positive SANE(14T) of +1.87×10-6 VK-1, revealing that the RE and 3d transition metal elements play the distinct roles on the transverse thermoelectric performance in RE2(Fe,Co)14B compounds.
Furthermore, we have developed the Nd2(Fe0.4Co0.6)14B permanent magnet to realize the high coercivity for zero field ANE device operations. The hot-pressed magnets were processed through the grain boundary diffusion process (GBDP) using Pr80Cu20 (~5wt.%) as a diffusion source for Nd2(Fe0.4Co0.6)14B alloys at optimized heat-treatment conditions. The GBDP samples had a fine grain with rare-earth (RE) rich IGP phases at grain boundaries. The formation of such non-ferromagnetic IGP reduces the intergranular exchange coupling, which results in increase in coercivity [6]. The GBDP sample shows SANE (0T) of +2.33×10-6 VK-1 measured at remanent state, which is higher than that of the ingots. These developed Nd2(Fe0.4Co0.6)14B permanent magnets excelled the promising transverse thermoelectric properties, which can be scale-up the zero field ANE power generation applications [3].
REFERENCES
[1] K. Uchida, Joule, 6 (2022) 2240–2245.
[2] A. Miura et al. Appl. Phys. Lett. 115 (2019) 222403.
[3] F. Ando, APL Energy. 2 (2024) 016103.
[4] F. Ando, Energy Environ. Sci. 2025(In press) [https://arxiv.org/abs/2402.18019].
[5] H. Sepehri-Amin et al. Acta Mater. 60 (2012) 819-830.
[6] H. Sepehri-Amin et al. Acta Mater. 99 (2015) 297-306.