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 − x Fe 80.8 + x B6 (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 Nd13.2Fe80.8B6 decreases to 7.2 kOe in Nd12.2Fe81.8B6; 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 Nd12.2Fe81.8B6/Tb17Fe75B8 magnets. These investigations show that magnetic properties can be further improved by regulating the element distribution in sintered composite magnets.