Regulating element distribution to improve magnetic properties of sintered Nd-Fe-B/Tb-Fe-B composite magnets

Nd content was varied in Nd_13.2-xFe_80.8+xB₆ (x=0, 0.5, 1, and 1.5) to optimize the magnetic properties of sintered Nd-Fe-B/Tb-Fe-B composite magnets, which were prepared by mixing 9 g of Nd-Fe-B with 1 g of Tb₁₇Fe₇₅B₈ powder. In conventional magnets, by reducing Nd content, the coercivity of 10.4 kOe in Nd_13.2Fe_80.8B₆ decreases to 7.2 kOe in Nd_12.2Fe_81.8B₆; meanwhile, in Nd-Fe-B/Tb-Fe-B magnets the coercivity does not decrease when reducing Nd content. In the intergranular phase, the Tb content increases owing to the reducing Nd content of the Nd-Fe-B alloy in the sintered composite magnets. Therefore, the excess Tb in Tb₁₇Fe₇₅B₈ enters the intergranular phase, and more Tb atoms can substitute for Nd at the grain boundary of the Nd-Fe-B phase, leading to a more significant increase in coercivity. The remanence increases with reducing Nd content, and the energy product of 39.1 MGOe with a high coercivity of 21.0 kOe is obtained in Nd_12.2Fe_81.8B₆/Tb₁₇Fe₇₅B₈ magnets. These investigations show that magnetic properties can be further improved by regulating the element distribution in sintered composite magnets.