EVIDENCE FOR REVERSAL BY NUCLEATION IN RE-FE-B DIE-UPSET MAGNETS

Electron microscopy and initial magnetization studies at elevated temp eratures were performed on two die-upset rare-earth magnets with bulk compositions Nd13.75Fe80.25B6 and Pr13.75Fe80.25B6. In both compositio ns the intergranular phase is amorphous and occurs primarily on those surfaces parallel to the tetragonal 2-14-1 phase c axis. The intergran ular phase is enriched in iron relative to the bulk grain, with an ave rage width of 8-12 Angstrom in the Nd-based magnet and 15-20 Angstrom in the Pr-based magnet. The initial magnetization curves and the depen dence of the coercivity upon maximum magnetizing field both increase l inearly with a common slope and then saturate, consistent with nucleat ion-dominated behavior. These results suggest that the dominant revers al mechanism in these magnets is nucleation of reversed domains in the iron-rich intergranular region of reduced anisotropy.