# Improvement of Hk and squareness in d-HDDR-treated Nd-Fe-B powders prepared using modified starting powder https://mdr.nims.go.jp/datasets/fda61f9a-3d91-43a8-b42c-c209829bb87e ## File - [REPM2025_P1-38_Horikawa.pdf](https://mdr.nims.go.jp/filesets/7b8a99ad-6a76-414a-a5d5-d4ad28027e08/download) ([Detail](https://mdr.nims.go.jp/filesets/7b8a99ad-6a76-414a-a5d5-d4ad28027e08.md)) - [(abstract) P1-38_Figure1.jpeg](https://mdr.nims.go.jp/filesets/e2a9acc5-3e69-4719-b748-3232b5307428/download) ([Detail](https://mdr.nims.go.jp/filesets/e2a9acc5-3e69-4719-b748-3232b5307428.md)) ## Id fda61f9a-3d91-43a8-b42c-c209829bb87e ## Local identifier ## Visibility open_to_public ## State published ## Created at 2025-09-01T00:28:04.904790Z ## Updated at 2025-09-11T07:31:46.492700Z ## Published at 2025-09-11T07:20:24.131509Z ## Doi https://doi.org/10.48505/nims.5691 ## First published url ## Date published ## Recorded date published ## Resource type conference_poster ## 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: Improvement of Hk and squareness in d-HDDR-treated Nd-Fe-B powders prepared using modified starting powder title_type: original lang: en ## Description - description: "By applying the dynamic hydrogenation-disproportionation-desorption-recombination (d-HDDR) process to Nd-Fe-B magnetic powder, high magnetic anisotropy and coercivity can be obtained [1]. We previously reported that in the preparation of the starting powder, annealing of the mother alloy at 700°C followed by hydrogen decrepitation at 500°C (referred to as the conventional method) can improve the single crystal ratio of the resultant powder and suppress crack formation in the Nd2Fe14B phase, leading to the formation of low anisotropic regions after d-HDDR. As a result, higher anisotropy was observed in the resultant d-HDDR-treated powder and in the bonded magnets fabricated using the powder [2,3]. However, the Hk and squareness (Hk/HcJ) of demagnetization curves were still low compared to those of commercially available sintered magnets, suggesting the existence of variations in coercivity and magnetic polarization among powder particles, as well as local variations of these properties within a single powder particle.\r\n\r\nIn our anisotropy induction model [2,3], the regions consisting of spherical NdH2+x grains and Fe matrix, which result in low anisotropic regions, tend to form near the surface of the powder particles after the hydrogen disproportionation step, irrespective of the powder size. As a result, the relative volume fraction of the low-anisotropy region varies with powder size, potentially inducing variations in the overall anisotropy and magnetic polarization among the powder particles. A similar trend is observed for coercivity. During the recombination step of the conventional d-HDDR treatment, the Nd-rich components in the starting powder diffuse into the Nd2Fe14B particles and form Nd-rich grain boundaries, which induce the coercivity. However, the distribution of grain boundary triple junctions appeared to show non-uniformity according to particle size, possibly leading to coercivity variations. Therefore, narrowing the size of starting powder particles is expected to contribute to reducing such variations. Furthermore, although an additional grain boundary diffusion process using fine Nd-Cu-Al alloy powder becomes necessary after the d-HDDR treatment, the removal of the Nd-rich components can result in more homogeneous grain boundaries and hence less variation in coercivity. Fig. 1. Demagnetization curves of d-HDDR-treated powders prepared using conventional and modified starting powders.\r\n\r\n\r\nIn this study, to improve the low Hk of d-HDDR-treated powders, the two modifications mentioned above were applied to the starting powder by sieving. First, the size range of the starting powder particles was narrowed from < 212 μm in the conventional method to 75–106 μm. Second, during this narrowing process, the excess Nd-rich grain boundary components present as fine particles (< 53 μm) in the starting powder, which are usually generated during the hydrogen decrepitation treatment, were simultaneously removed. After these modifications, the Hk and squareness increased from 0.81 MA/m and 61%, respectively, for the conventional d-HDDR to 0.98 MA/m and 73% (Fig. 1).\r\n\r\n[1] C. Mishima et al., IEEE Trans. Magn., 37 (2001) 2467.\r\n[2] T. Horikawa et al., Sci. Tech. Adv. Mater., 22 (2021) 729.\r\n[3] T. Horikawa et al., The 170th Annual meeting of JIM, (2022) S7.2." description_type: abstract lang: en ## Creator - name: Takashi Horikawa role: author organization: Aichi Steel Corporation, Japan - name: Masao Yamazaki role: author organization: Aichi Steel Corporation, Japan - name: Masashi Matsuura role: author organization: Tohoku University, Japan - name: Satoshi Sugimoto role: author organization: Tohoku University, Japan ## Contact agent ## Publisher organization: National Institute for Materials Science (NIMS) ## Managing organization ## Keyword - subject: REPM2025 schema: not_defined - subject: Nd-Fe-B magnet powder schema: not_defined - subject: HDDR schema: not_defined - subject: Hk schema: not_defined - subject: squareness schema: not_defined - subject: powder diameter 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: 7b8a99ad-6a76-414a-a5d5-d4ad28027e08 filename: REPM2025_P1-38_Horikawa.pdf content_type: application/pdf size: 2626426 md5: ade50e524ce769c881aa4e96761e4a87 - id: e2a9acc5-3e69-4719-b748-3232b5307428 filename: "(abstract) P1-38_Figure1.jpeg" content_type: image/jpeg size: 48647 md5: 4d39aaa4afdfdd561306b28f68278c80 ## Thumbnail fileset_id: 7b8a99ad-6a76-414a-a5d5-d4ad28027e08 filename: REPM2025_P1-38_Horikawa.pdf