# Accelerated development of thermally stable Nd-Fe-B magnets with light rare-earth elements and their synergetic effects to temperature stability with Co https://mdr.nims.go.jp/datasets/1afc26ef-f6cf-41ea-aa4e-44997b06b533 ## File - [REPM2025_O16-2_Zhang.pdf](https://mdr.nims.go.jp/filesets/f9f7ae79-8be6-4417-8912-59e6ec12445d/download) ([Detail](https://mdr.nims.go.jp/filesets/f9f7ae79-8be6-4417-8912-59e6ec12445d.md)) ## Id 1afc26ef-f6cf-41ea-aa4e-44997b06b533 ## Local identifier ## Visibility open_to_public ## State published ## Created at 2025-09-01T03:36:17.260833Z ## Updated at 2025-09-11T07:31:51.119515Z ## Published at 2025-09-11T07:20:02.279419Z ## Doi https://doi.org/10.48505/nims.5692 ## First published url ## Date published ## Recorded date published ## Resource type conference_presentation ## Manuscript type na ## Collection - id: d28f086a-61aa-4bc7-bcae-5a1078cbc6c7 identifier: https://mdr.nims.go.jp/pid/d28f086a-61aa-4bc7-bcae-5a1078cbc6c7 title: The 28th International Workshop on Rare Earth and Future Permanent Magnets and Their Applications (REPM2025) ## Title - title: Accelerated development of thermally stable Nd-Fe-B magnets with light rare-earth elements and their synergetic effects to temperature stability with Co title_type: original lang: en ## Description - description: Developing Nd-Fe-B-based permanent magnets with exceptional high-temperature stability is critical for extending their use in traction motors operating at temperatures of ~150℃. Traditionally, the temperature stability of the Nd-Fe-B magnet can be improved by elements with high Tc such as Co or heavy rare-earth elements (HRE) such as Dy and Tb, etc, which inevitably increases the cost. Doping with cost-effective light rare-earth elements (LRE) such as La, Ce and Y and leveraging the temperature stability with Co and Ni are highly desired to enhance the competitiveness of magnets in the market. Unlike the conventional trial-and-error way, we applied the ‘adaptive’ learning framework (based on Bayesian Optimization) in the composition optimization of Nd-Fe-B sintered magnets towards improved performance-cost ratio. By systematic substitution in the RE-TM-B pseudo-ternary system where RE=NdPr, La, Ce, Y and TM=Fe, Co, Ni, we designed 24 compositions based on [(Nd0.8Pr0.2)(1-x)(La/Ce/Y)x]13.86[Fe(1-y)(Co/Ni)y]77.10M3.30B5.74 (M=Al, Cu, Ga, Ti, at.%) as the starting point of iteration. These magnets were composed of >97% of the RE2TM14B matrix phase and minor phases such as the fcc-NdOx, Ia-3-NdOx, NdFe4B4, and RETM2 Laves phase. 9 novel compositions were recommended within 3 iterations, which were then experimentally prepared, and their magnetic properties measured. It is found that the La-Co, Ce-Co, and La-Co-Ni combinations outperform the other combinations. The best two candidates identified in the last iteration showed 18.4% and 13.1% improvement in performance-cost ratio to benchmark Nd-Fe-B, respectively. An unexpected synergetic effect by co-doping with LRE and Co to improve the temperature stability of the remanence of the magnet is discovered in the present work. It is shown that the remanence at 150℃ and its temperature coefficient α (20-150℃) are 1.099 T and -0.087%/℃ after La-Co co-doping, outperforming the 1.093 T and -0.134%/℃ of the undoped magnet. Regarding remanence and its α, doping with the La-Co pair shows a favourable effect over the Ce-Co pair. Compared with doping with Co alone, the α (20-150℃) of the La0.25Co0.25 and Ce0.25Co0.25 co-doped magnets are almost the same as that of the Co0.25 one even though their Tc are 87°C and 136°C lower. Statistical results from the atomic resolution STEM-EDS indicate that La preferentially occupies the 4g-site of the 2:14:1 lattice in the La0.25Co0.25 magnet, while Ce, the 4f-site in the Ce0.25Co0.25 magnet. Mössbauer spectroscopy reveals that Co preferentially occupies the 16k1, 16k2 and 8j2 sites in the Co0.25 and La0.25Co0.25 magnets, while the 16k1, 16k2 and 8j1 sites in the Ce0.25Co0.25 magnet. Density functional theory calculations based on the preferential site occupations of Ce, La and Co in the 2:14:1 lattice determined by atomic resolution STEM-EDS and Mössbauer spectrum were performed and found that there are spikes and spin splitting at ~10 eV above the Fermi level by La-Co co-doping, which can explain the improved temperature stability. Compared with the benchmark data, the temperature coefficients of remanence of the La-Co co-doped magnets outperform many commercial and reported ones, which is inspiring to develop thermally stable and cost-effective magnets by LRE without HRE. description_type: abstract lang: en ## Creator - name: Xinyi Ji role: author organization: Shanghai Jiao Tong University, China - name: Lanting Zhang role: author organization: Shanghai Jiao Tong University, China - name: Hong Zhu role: author organization: Shanghai Jiao Tong University, China - name: Zhaozhe Zhong role: author organization: Toyota Motor Technical Research and Service (Shanghai) Co., Ltd, China - name: Jian Liu role: author organization: Toyota Motor Technical Research and Service (Shanghai) Co., Ltd, China - name: Zhanji Dong role: author organization: Yantai Dongxing Magnetic Materials Inc, China - name: Zhongjie Peng role: author organization: Yantai Dongxing Magnetic Materials Inc, China - name: Kaihong Ding role: author organization: Yantai Dongxing Magnetic Materials Inc, China ## Contact agent ## Publisher organization: National Institute for Materials Science (NIMS) ## Managing organization ## Keyword - subject: REPM2025 schema: not_defined - subject: Nd-Fe-B magnet schema: not_defined - subject: light rare-earth elements schema: not_defined - subject: Bayesian optimization schema: not_defined - subject: temperature stability schema: not_defined - subject: site occupation schema: not_defined ## Rights - identifier: https://creativecommons.org/licenses/by/4.0/ ## Other identifier(s) ## Data origin - data_origin_type: other ## Embargo ## Journal ## Conference name: REPM2025 start_date: 2025-07-27 end_date: 2025-07-31 identifier: https://www.nims.go.jp/mmu/repm2025/ ## Related item ## Funding ## Instrument ## Instrument operator ## Instrument managing organization ## Measurement method ## Specimen ## Chemical composition ## Structure for specimen ## Structural feature for specimen ## Specific property for specimen ## Process for specimen treatment ## Computational method ## Energy level/transition state ## Software ## Custom property ## Fileset - id: f9f7ae79-8be6-4417-8912-59e6ec12445d filename: REPM2025_O16-2_Zhang.pdf content_type: application/pdf size: 3446402 md5: 53653a341a21728cc17ab64eb15b4802 ## Thumbnail fileset_id: f9f7ae79-8be6-4417-8912-59e6ec12445d filename: REPM2025_O16-2_Zhang.pdf