Magnetic domain observation of Nd-Cu-diffused Nd-Fe-B magnets with submicron grains by Kerr effect microscopy.

The domain structure and magnetization process of Nd-Cu-diffused magnets prepared from hydrogenation-disproportionation-desorption-recombination (HDDR)-processed powders and Nd-Cu powders were examined with a high-resolution Kerr microscope using an ultraviolet light source. We found that the coercivity of the HDDR magnet depends on the volume of magnetically coupled grains that simultaneously reverse their magnetization. In a magnet that has no Nd-Cu, and in which the Nd-rich phase along the grain boundaries is absent, magnetization reversal simultaneously occurs in several grains. In contrast, in a Nd-Cu-diffused magnet that contains adequate Nd-rich phases along the grain boundaries, magnetization reversal occurs independently in each grain. It follows that the change in microstructure caused by the presence of Nd-Cu leads to a decoupled magnetization reversal, and domain wall pinning is an important coercivity mechanism of an HDDR magnet compacted by hot-pressing. [ABSTRACT FROM AUTHOR]