Improvement in intrinsic coercivity of sintered Fe-Nd-B magnets by the introduction of non-magnetic dispersoids

The microstructure of Ho-substituted sintered Fe-Nd-B magnets, prepared by two different routes, has been characterized in order to understand the changes in intrinsic coercivity with Ho content. Spherical inclusions in the size range of 500 Å-l μm have been observed inside the matrix Re2Fe14B grains. Characterization by X-ray diffraction, electron microdiffraction and energy dispersive X-ray microanalysis, shows that these inclusions are f.c.c. rate earth oxides. The volume fraction of these inclusions increases with Ho content. Ho partitions preferentially into the matrix phase and no segregation of Ho to the interphase interfaces is observed. Lorentz electron microscopy experiments suggest that the inclusions in the lower end of the size distribution are capable of pinning the magnetic domain walls and hence these non-magnetic inclusions must contribute to the increase in intrinsic coercivity. © 1989.