# Fileset

[REPM2025_P2-56_Gao.pdf](https://mdr.nims.go.jp/filesets/1cda8098-5985-4e72-a291-2ac89071c359/download)

## Creator

Qiang Gao, Dong Liang, Hui-Dong Qian, Tao Zhu, Jingzhi Han, Changsheng Wang, Wenyun Yang, Jinbo Yang

## Rights

[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

## Other metadata

[Rapid Preparation of Sm2Fe17N3 Fine Powder by Cryo-milling](https://mdr.nims.go.jp/datasets/aa2b8476-d4ef-41f2-b174-c80a4704ed7a)

## Fulltext

Qiang Gao, Dong Liang, Hui-Dong Qian, Tao Zhu, Jingzhi Han, Changsheng Wang, Wenyun Yang, Jinbo YangBeijing Key Laboratory for Magnetoelectric Materials and Devices, Beijing 100871, China.Institute of Condensed Matter and Material Physics, School of Physics, Peking University, Beijing, 100871, ChinaE-mail: yangwenyun@pku.edu.cnRapid Preparation of Sm2Fe17N3 Fine Powder by Cryo-millingPoster PresentationIntroduction➢Samarium iron nitride (Sm2Fe17N3) permanent magneticmaterials possess excellent intrinsic magnetic properties, including a saturation magnetization of 1.54 T. To reach the full potential, the key is to increase the coercivity of the powder. Since the coercivity mechanism of Sm2Fe17N3 is nucleation-controlled, reducing the grain size through grinding is a necessary step in preparing high-performance powders for Sm2Fe17N3 magnets.➢Due to the high chemical reactivity, Sm₂Fe₁₇N₃ readily oxidizesduring ball milling, forming Sm₂O₃ and soft-magnetic Fe thatdegrade the magnetic properties. Meanwhile, the localizedhigh temperatures generated during milling can decomposeSm₂Fe₁₇N₃ into SmN and Fe, thereby compromising themagnetic performance.This Work➢Here, we therefore investigate a liquid-nitrogen-cooled millingprocess (cryo-milling) for rapidly producing high-coercivitySm₂Fe₁₇N₃ fine powder, which significantly boosts productionefficiency and ensures superior batch-to-batch quality stability.Coercivity Characterization➢By using the equipment named Freezer/Mill, the Sm₂Fe₁₇N₃coarse powder was ground by cryo-milling method at liquidnitrogen temperature. After 1 minute of grinding, thecoercivity of the Sm₂Fe₁₇N₃ powder went up from 1.5 kOe to7.0 kOe, while after 4 minutes, the coercivity reached 13.4 kOe.However, as the grinding time increased further, the coercivitybegan to decrease.➢As a control experiment, we used conventional ball-milling: thesame Sm₂Fe₁₇N₃ coarse powder was loaded into a jar togetherwith stainless-steel balls and n-heptane acting as an oxygenand moisture barrier solvent. Only after a prolonged millingtime of 120 min did the coercivity reach 13.3 kOe, comparableto the cryo-milling result in just 4 min.X-ray Diffraction Results➢X-ray diffraction (XRD) results indicated that no α-Fe phase wasgenerated during the grinding process, and the Sm₂Fe₁₇N₃diffraction peaks broadened continuously with increasinggrinding time, showing that the liquid nitrogen conditionsinhibit oxidation and thermal decomposition during the millingprocess of Sm₂Fe₁₇N₃, and as the grinding time increases, thegrain size of the Sm₂Fe₁₇N₃ powder continuously decreases.Microscale Morphological Features➢Scanning electron microscope (SEM) results showed that thesample ground for 4 minutes by cryo-milling (Fig. a) had asimilar particle size to that of the sample ground for 120minutes by conventional ball milling (Fig. b). This indicates thatthe material becomes more brittle at low temperatures,making it easier to break.10.0μm 10.0μm(a) (b)Conclusions➢Cryo-milling produce Sm₂Fe₁₇N₃ powder with similar coercivityand particle size to that obtained by conventional tumbling ballmilling, yet in only 1/30 of the time—markedly faster and moreefficient. It does not require the use of conventional solvents,is more efficient, and effectively avoids heat and oxidationissues during the grinding process. The cryo-milling methodthus provides a promising approach to fabricate high-performance Sm2Fe17N3 powder.Sm2Fe17N3 original coarse powderSm2Fe17N3 cryo-milling result in 5 minutesSm2Fe17N3 cryo-milling result in 50 minutes2θ (deg)Intensity (a.u.) 幻灯片 1 幻灯片 2