Preparation of Mn-diffused Sm-Fe-N core-shell powder by reduction-diffusion process

• Published in: Journal of magnetism and magnetic materials 2019-02, Vol.471, p.310-314
• Main Authors: Matsuura, Masashi, Yarimizu, Keisuke, Osawa, Yohei, Tezuka, Nobuki, Sugimoto, Satoshi, Ishikawa, Takashi, Yoneyama, Yukinobu
• Format: Article
• Language: English
• Subjects: Coercivity; Crystal structure; Diffusion; Magnetic properties; Magnetic saturation; Magnetism; Magnetization; Manganese; Microprocessors; Reduction; Reduction-diffusion process; Shell stability; Sm2Fe17Nx/Sm2(FeMn)17Nx core-shell powder; Thermal stability
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2018.09.084

•This is the first report to prepare Sm2Fe17Nx-core/Sm2(Fe,M)17Nx-shell powder by reduction diffusion (RD) process.•Mn diffused from Sm2Fe17 powder during RD process, and the diffusion length was 0.8 μm.•The saturation magnetization of the core-shell powder was higher than that of Sm-Fe-Mn-N (not core-shell) powder.•Thermal stability of the Mn-diffused Sm-Fe-N core-shell powder was higher than that of Sm-Fe-N powder without Mn diffusion. Although the addition of other elements such as Mn to Sm2Fe17Nx compounds can change the magnetic properties, it also decreases saturation magnetization. In order to exploit the advantages of additional elements in Sm2Fe17Nx powder while maintaining a high saturation magnetization, a structure of Sm2Fe17Nx-core/Sm2(Fe,M)17Nx-shell is promising. This is the first report of such a core-shell powder obtained by a reduction-diffusion process. Mn3O4 was mixed with Sm-Fe and Sm2O3 powders followed by the reduction by Ca above 860 °C, and then samples were nitrided and washed after reduction-diffusion process. Core-shell Sm-Fe-N fine powder with a Mn-enriched Sm2(Fe,Mn)17Nx shell was thus successfully obtained. The thickness of the Mn enriched region was about 0.8 μm, and the crystal structure of the core-shell powder was Th2Zn17. The saturation magnetization and coercivity of the core-shell powder were 138.8 A·m2·kg−1 and 1001.7 kA·m−1, respectively. The saturation magnetization was slightly smaller than that of Mn-free Sm-Fe-N powder, whereas the coercivity of the core-shell powder was higher than that of Mn-free Sm-Fe-N powder. In addition, the saturation magnetization and coercivity were higher than those reported for Sm-Fe-Mn-N powder. The thermal stability of the Mn-diffused Sm-Fe-N core-shell powder was improved compared with Mn-free Sm-Fe-N powder.