Magnetic anisotropy of RE-magnets

A brief survey is given of the most recent results in the study of magnetic anisotropy in RE intermetallic compounds of interest for permanent magnet applications. Among these the 1:5 and 2:17 phases are those that have received the largest attention in the past years, and their properties are understood to a satisfactory level. Since 1984 the attention of most laboratories in the world has been strongly attracted by Nd2Fe14B, the new permanent magnet material discovered by Sagawa and coworkers at Sumitomo in Japan. Its magnetic anisotropy is mainly due to the RE component, and a very large number of compositions have already been investigated. The overall anisotropy is the result of a complex interplay between multiple and competing subblattice anisotropies and exchange field. The complexity of the situation is withnessed by the rich phenomenology displayed by various isostructural ternary compounds and solid solutions, with the presence of magnetic transitions of first and second order both spontaneous and field induced. There is at present a better understanding of the basic mechanisms responsible for the anisotropic behavior of this new family of Fe based alloys, but a number of problems connected with the role of exchange interaction, band structure effects, lattice parameters, cationic site distribution and competing anisotropies still remain.