Phase transformations and coercivity in rare-earth permanent magnets

Abstract The hypothetic Sm–Co and Nd–Fe phase diagrams are compared. The phase transformations, which may cause boundaries modification of the SmCo5 and Nd2Fe14B phases, are considered. The phase transformation-induced coercivity mechanism in both Sm–Co and Nd–Fe–B sintered magnets are suggested. It is supposed that formation of coherent epitaxial layers at the surface of grains of the principal phase decreases the number of defect sites for nucleation of reversal magnetization domains and increases the coercive force.