Effect of grain-boundary phases in Y- and Ce-substituted R_2Fe_(14)B sintered magnets

摘要

Sintered R_2Fe_(14)B (R: rare earth element) magnets with a 50% Y- and Ce-substitution for Nd were studied with the goal of reducing the Nd content. Nd was substituted with Y to attain greater magnetization and with Ce for higher coercivity. In the composition with a Y:Ce = 1:1 substitution, a maximum energy density of 355 kJ/m~3 (44.6 MGOe) was achieved with a residual flux density of 1.38 T and a coercivity of 533 kA/m. To improve the coercivity, the effect of adding Ga was investigated to introduce a R_6Fe_(13)Ga grain-boundary phase and thus achieve magnetic separation between the grains. As a result of adding 1.0-3.0 at% Ga, although R_6Fe_(13)Ga formed at the grain boundaries, the coercivity decreased due to the large magnetization of 0.3-0.5 T. The magnetization of the RFe_2 grain boundary phase decreased with an increase in the Ce concentration, and fell to 0.05 T for Ce 100%. By introducing the RFe_2 grain-boundary phase with an appropriate amount of Ce, a coercivity of 1063 kA/m (13.4 kOe) with a residual flux density of 1.22 T was achieved with a Ce content of 40% of the rare earth elements in a R_2Fe_(14)B sintered magnet.