Optimal design of sintered Ce₉Nd₂₁Fe_balB₁ magnets with a low-melting-point (Ce,Nd)-rich phase

A systemic investigation was done on the chemistry and crystal structure of boundary phases in sintered Ce₉Nd₂₁Fe_balB₁ (wt%) magnets. Ce₂Fe₁₄B is believed to be more soluble in the rare-earth (RE)-rich liquid phase during the sintering process. Thus, the grain size and oxygen content were controlled via low-temperature sintering, resulting in high coercivity and maximum energy products. In addition, Ce formed massive agglomerations at the triple-point junctions, as confirmed by elemental mapping results. Transmission electron microscopy (TEM) images indicated the presence of (Ce,Nd)O_x phases at grain boundaries. By controlling the composition and optimizing the preparation process, we successfully obtained Ce₉Nd₂₁Fe_balB₁ sintered magnets; the prepared magnets exhibited a residual induction, coercivity, and energy product of 1.353 T, 759 kA/m, and 342 kJ/m³, respectively.