Phases and phase equilibria in cobalt-rich Pr-Co-In alloys for permanent magnets

The Pr-Co-In phase equilibria related to the indium-added PrCo5 permanent magnets have been systematically studied. The 800 °C isotherm and the PrCo5-PrCo2In polythermal section reveal several compounds never reported for this system. One of them, the orthorhombic Pr3Co9In2, forms peritectically at 957 °C and it is believed to be responsible for the increased coercivity of Pr-Co-In sintered magnets subjected to a post-sintering annealing. The Pr3Co9In2 compound forms a two-phase equilibrium with PrCo5; it is paramagnetic at room temperature and exhibits an antiferromagnetic ordering at 198 K. Also observed were the hexagonal PrIn2 compound possibly stabilized by a small amount of cobalt and an unidentified ternary phase with the approximate composition Pr45Co15In40. The work provides recommendations for the development and improvement of PrCo5 permanent magnets via indium additions.