Magnetic properties of a Nd-Fe-B sintered magnet with Dy segregation

The magnetic properties and microstructures of a Nd-Fe-B sintered magnet with Dy segregation obtained by applying a fluoride-solution technique were studied using transmission electron microscopy and micromagnetic analysis. By applying 0.1-0.2 wt% fluorides in comparison with weight of the magnet and heating the magnet, coercivity increased by about 1.3 times from 1.1 to 1.4 T at 298 K while retaining remanence. Dy segregated within about 250 nm from the grain surfaces and coercivity was controlled by the area near the grain boundaries. Furthermore, we estimated that the range for reducing the magnetic anisotropy field near the grain boundaries was one or two unit cells by applying micromagnetic analysis to the magnet, which may indicate larger coercivity with less Dy. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3073830]