First-principles study of site preferences for Fe in Sm(CoFeCuZr)z permanent magnets

Sm(CoFeCuZr)z permanent magnets are of great technological interest due to their good magnetic performance and excellent thermal stability. The Fe content plays a key role for magnetic properties, determining the maximum energy product and the highest working temperature. Here we investigated the Fe site preferences in Sm(CoFeCuZr)z magnets with Fe content up to 26 wt. %, the solubility limit in sintered magnets by first-principles calculations. It is shown that Fe dissolves preferably in the rhombohedral Th2Zn17-type (2:17 R) phases, with a strong preference for the dumbbell (6c) sites. After 6c sites are fully occupied, Fe distributes in 18f sites as scattered as possible. The crystal structures of 2:17 R type Sm2(Co,Fe)17 lattice were presented with varying Fe content. The calculated structure and magnetic properties were analyzed comparing with experimental results of 2:17 R phases in multicomponent alloys. Also, the gradually increased substitution energy with continuous doping explained the difficulty in preparation of Sm(CoFeCuZr)z magnets with much Fe.