Phase, chemical constitution and effective depth of oxide overgrowth and its influence on SmPrCo5 magnetic properties

Abstract

Ternary Sm-Pr-Co magnets with CaCu5-type hexagonal structure exhibit superior magnetic properties and investigating their oxidation behavior is crucial for assessing their stability under the service conditions. In this regard, here thermal oxidation of sintered SmPrCo5 magnet is carried out by varying the oxidation temperature from 373 to 973 K for 5 hr under atmospheric pressure. Owing to their lower negative Gibbs free energy, rare earth oxides of Sm2O3 and Pr2O3 are found to initially form, making cobalt free from SmPrCo5 lattice. Cobalt is then observed to migrate to the oxide surface, because of the difference in chemical potential between the surface and inner layers, leading to Co3O4 formation. Moreover, here a comprehensive discussion on the occurrences of different oxide phases and their depth distributions in the oxide layer are being made. Finally, a correlation between these oxide phases and the alterations in their magnetic properties is discussed.