Disclinations: The magnetism and the magnetic anisotropies of the rare‐earth–3d transition‐metal hard magnets (invited)

An important class of hard magnets, involving rare earth and 3d transition metals and sometimes metalloids, includes Nd2Fe14B and Nd2Fe17. We have noted a correlation between the local site magnetism in these two compounds and whether those sites lie on nets of so‐called major ligand lines or disclinations, i.e., bond lines shared by six common nearest neighbors. We have proposed that a criterion for choosing candidate alloys with strong 3d moments is the occurrence of such disclination nets, and using this criterion, have listed several structures having 3d sites with this characteristic. We have also rationalized the crystal field anisotropies as relating to the orientation of the major ligand lines.