Development of TbCu7-type Sm-Fe-N anisotropic magnet powder and its sintered magnets

Anisotropic TbCu7-type Sm-Fe-N magnet powder and its sintered magnets were developed using TbCu7-type Sm-Fe alloy powder synthesized by a modified low-temperature reduction diffusion process. Using Sm metal powder instead of SmCl3 and Ca and using the eutectic salt LiCl-CaCl2 to lower the synthesis temperature, an almost single-phase TbCu7-type Sm-Fe powder was obtained. By nitriding the powder with an NH3-H2 mixture gas, a TbCu7-type Sm-Fe-N anisotropic magnet powder was demonstrated for the first time. Furthermore, by sintering the anisotropic powder with a high-pressure current sintering process, a TbCu7-type Sm-Fe-N anisotropic sintered magnet with a relative density of 86.8% was produced. The magnetization ratio σr/σ90 kOe was decreased by the formation of the α-Fe phase as a result of the decomposition of the TbCu7-type Sm-Fe-N phase in the sintering process, whereas the coercivity was slightly increased. This result indicates that the TbCu7-type Sm-Fe-N magnet is less affected by the existence of α-Fe compared with a Sm2Fe17N3 magnet. •High-purity metastable TbCu7-type Sm-Fe alloy powder was obtained by a modified low-temperature reduction diffusion process.•By nitriding the obtained powder, TbCu7-type Sm-Fe-N anisotropic magnet powder was demonstrated for the first time.•TbCu7-type Sm-Fe-N anisotropic sintered magnet with a relative density of 86.8% was produced by current sintering.