Microstructure, microchemistry, and micro-magnetism of Dy grain boundary diffused (Nd, Ce)–Fe–B magnets

The microstructure of (Nd, Ce)–Fe–B sintered magnets with different diffusion depths was characterized by a magnetic force microscope, and the relationship between the magnetic properties and the local structure of grain boundary diffused magnets is discussed. The domains perpendicular to the c-axis (easy magnetization direction) show a typical maze-like pattern, while those parallel to the c-axis show the characteristics of plate domains. The significant gradient change is shown in the concentration of Dy with the direction of diffusion from the surface to the interior. Dy diffuses along grain boundaries and (Dy, Nd)2Fe14B layer with a high anisotropy field formed around the grains. Through in-situ electron probe micro-analysis/magnetic force microscopy (EPMA/MFM), it is found that the average domain width decreases, and the proportion of single domain grains increases as diffusion depth increases. This is caused by both the change of concentration and distribution of Dy. The grain boundary diffusion process changes the microstructure and microchemistry inside the magnet, and these local magnetism differences can be reflected by the configuration of the magnetic domain structure.