Effect of Particle Size on the Magnetic Properties and Initial Permeability of Sintered Nd-Fe-B Magnets

The Nd-Fe-B magnet with nominal composition of (Pr25Nd75)(25)Dy6Al0.5B1Co1Cu0.2Febal was prepared by a traditional powder metallurgy method. The magnetic properties and initial magnetization permeability of the Nd-Fe-B from magnetic powders with different particle sizes were investigated. The results show that the magnet from the particles with an average size of 3.0 mu m achieves the best H-cj, and the particles with an average size of 3.5 mu m obtains the best B-r. The refined particle size of 3.0 mu m makes the morphology regular and uniform. But as the average particle size further decreases, the Nd rich phase is in the form of an oxide and unevenly distributed at the grain boundary, and the demagnetization coupling efficiency drops, resulting in a decrease in H-cj. The oxygen content increases as the average size becomes smaller, and B-r decreases as the impurity content increases. On the other hand, the initial permeability dramatically falls with the increasing impurity content.