Rare-earth Lean Sm(Fe0.8Co0.2)12-B Thin Film Magnet
By adding the light element B to Sm(Fe0.8Co0.2)12, which contains a low amount of rare-earth elements, a high coercivity of 1.2 Tesla—sufficient for industrial applications such as automotive motors—was successfully achieved in a thin-film model experiment. In order to elucidate the mechanism of this property-microstructure relationship, detailed nanoscale structural analysis was conducted using scanning transmission electron microscopy (STEM) and atom probe tomography (APT), revealing that the Sm(Fe0.8Co0.2)12 nanocrystalline particles are uniformly covered by an B-rich amorphous phase with a thickness of approximately 3 nm, forming a unique multiphase nanostructure. Furthermore, the material exhibits an anisotropic structure with crystal orientations aligned in one direction, thereby achieving higher magnetization compared to conventional isotropic materials. To date, anisotropic Sm(Fe0.8Co0.2)12 has not exhibited sufficient coercivity; however, by applying the coercivity mechanism established in this study to bulk magnets, the development of practical anisotropic Sm(Fe0.8Co0.2)12 magnets is expected.
- H. Sepehri-Amin, Y. Tamazawa, M. Kambayashi, G. Saito, Y.K. Takahashi, D. Ogawa, T. Ohkubo, S. Hirosawa, M. Doi, T. Shima, and K. Hono, "Achievement of high coercivity in Sm(Fe0.8Co0.2)12 anisotropic magnetic thin film by boron doping", Acta Mater. 194, 337 (2020)
- A. Bolyachkin, H. Sepehri-Amin, M. Kambayashi, Y. Mori, T. Ohkubo, Y.K. Takahashi, T. Shima, K. Hono, "Coercivity engineering in Sm(Fe0.8Co0.2)12B0.5 thin films by Si grain boundary diffusion", Acta Mater. 227, 117716 (2022)
- Sepehri-Amin, N. Kulesh, Y. Mori, T. Ohkubo, K. Hono, and T. Shima, "Microstructure and coercivity of Al-diffused Sm(Fe,Co,B)12 film", Scr. Mater. 242, 115955 (2024)
Regarding This Research:
Hossein SEPEHRI-AMIN, Group Leader of Green Magnetic Materials Group at NIMS
E-mail: H.SEPEHRIAMIN[at]nims.go.jp