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

Abstract The Pr–Co–In phase equilibria related to the indium-added PrCo 5 permanent magnets have been systematically studied. The 800 °C isotherm and the PrCo 5 –PrCo 2 In polythermal section reveal several compounds never reported for this system. One of them, the orthorhombic Pr 3 Co 9 In 2 , 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 Pr 3 Co 9 In 2 compound forms a two-phase equilibrium with PrCo 5 ; it is paramagnetic at room temperature and exhibits an antiferromagnetic ordering at 198 K. Also observed were the hexagonal PrIn 2 compound possibly stabilized by a small amount of cobalt and an unidentified ternary phase with the approximate composition Pr 45 Co 15 In 40 . The work provides recommendations for the development and improvement of PrCo 5 permanent magnets via indium additions.