Evidence for reversal by nucleation in RE‐Fe‐B die‐upset magnets

Electron microscopy and initial magnetization studies at elevated temperatures were performed on two die‐upset rare‐earth magnets with bulk compositions Nd13.75Fe80.25B6 and Pr13.75Fe80.25B6. In both compositions the intergranular phase is amorphous and occurs primarily on those surfaces parallel to the tetragonal 2‐14‐1 phase c axis. The intergranular phase is enriched in iron relative to the bulk grain, with an average width of 8–12 A in the Nd‐based magnet and 15–20 A in the Pr‐based magnet. The initial magnetization curves and the dependence of the coercivity upon maximum magnetizing field both increase linearly with a common slope and then saturate, consistent with nucleation‐dominated behavior. These results suggest that the dominant reversal mechanism in these magnets is nucleation of reversed domains in the iron‐rich intergranular region of reduced anisotropy.