Sm-Fe-based alloy has variety phases e.g. ThMn12-, Th2Zn17-, Th2Ni17-, TbCu7-structures. The Sm2Fe17N3 compound with Th2Zn17 structure has high anisotropy field, Curie temperature and saturation magnetization [1,2], therefore this compound is expected for magnet with high thermal stability. The Sm2Fe17N3 based powder with particle size below ~5 m is commercially available for bonded magnets, however its coercivity decreases after heating above 180-200 C due to reasons such as surface oxidation. This issue prevents applying it for injection molding bonded magnets, therefore it is necessary to improve their thermal stability. Although Mn added Sm2(Fe,Mn)17Nx was reported to show high thermal stability with increasing nitrogen content [3], saturation magnetization decreased. To achieve high saturation magnetization and high thermal stability simultaneously, we developed Mn diffused core-shell structure Sm2Fe17Nx powder [4]. Furthermore, the TbCu7-type Sm-Fe-based alloy has high saturation magnetization because of higher Fe ratio than Sm2Fe17Nx compounds. Recently, our group focused on the Sm-Fe-Co-Nb-B alloy system. We achieved a high coercivity of 655 kAm-1 without nitriding and clarified fine microstructure with Sm-less grain boundary phase [5], indicating the alloy can be applicable for rare-earth-less permanent magnets. In this talk, I am going to introduce recent research trends and our study of Sm-Fe-based magnets.

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[2]T. Iriyama, K. Kobayashi, N. Imaoka, and T. Fukuda, IEEE Trans. Magn., 28 (1992) 2326-2331.
[3] N. Imaoka, T. Iriyama, S. Itoh, A. Okamoto, and T. Katsumata, J. Alloy. Compd., 222, (1995) 73-77.
[4] M. Matsuura, K. Yarimizu, K. Osawa, N. Tezuka, S. Sugimoto, T. Ishikawa and Y. Yoneyama, J. Magn. Magn.Mater., 471 (2019) 310-314.
[5]N. Kurokawa, M. Matsuura, S. Sakurada, and S. Sugimoto, J. Magn. Magn. Mater., 556 (2022) 169414_1-9.