Magnetic properties of Mn diffused Sm2Fe17Nx core-shell powder by reduction diffusionprocess

Abstract

Sm2Fe17Nx compounds have high anisotropy field, Curie temperature and saturation magnetization, thereforethis compound is expected for magnet with high thermal stability. Sm2Fe17Nx based Sm-Fe-N powder withsmall particle size below about 3 m can show high coercivity at room temperature, however coercivitydropped after heating above 150-200℃ . To enhance thermal stability of Sm-Fe-N powder, Mn addition waseffective. Imaoka et al[1] reported that Mn added Sm2(Fe,Mn)17Nx powder (x>3) showed high thermal stabilitywith increasing nitrogen content, however saturation magnetization decreased with increasing nitrogencontent. To achieve high saturation magnetization and high thermal stability simultaneously, Sm2Fe17Nx core- Sm2(Fe,Mn)17Nx shell structure is promising. Thus, the purpose of this study is preparation of Mn-diffusedSm2Fe17Nx core-shell particle by reduction diffusion process. Sm2Fe17 coarse powder, Mn3O4 and Sm2O3powders were pulverized and mixed by ball milling. After Ca grain mixing, the mixed powder was heated abovemelting temperature of Ca. Then, it was heat treated at 400℃ in N2 gas for nitriding, and the nitrided powderwas washed for removing residual Ca and CaO. Magnetic properties of powder was measured by VSM,microstructure was observed SEM and crystal structure was identified by XRD. Figure 1 shows SEM imageand Mn-mapping of Mn-diffused Sm-Fe-N powder prepared in this study. SEM image shows particle size ofSm-Fe-N powder was around 3-5 m, and Mn was enriched at the surface of Sm-Fe-N powder. XRD analysisindicated that crystal structure of the Mn-diffused Sm-Fe-N powder was Th2Zn17 structure. Therefore, it isconsidered that Mn-diffused Sm2Fe17Nx core-shell particle was obtained. Saturation magnetization of thecore-shell powder was higher than that of Sm-Fe-Mn-N powder which was reported in previous studies.