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

$\mathrm{Sm}{(\mathrm{CoFeCuZr})}_{z}$ 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 $\mathrm{Sm}{(\mathrm{CoFeCuZr})}_{z}$ 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 $\mathrm{T}{\mathrm{h}}_{2}\mathrm{Z}{\mathrm{n}}_{17}$-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 $\mathrm{S}{\mathrm{m}}_{2}{(\mathrm{Co},\phantom{\rule{0.16em}{0ex}}\mathrm{Fe})}_{17}$ 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 $\mathrm{Sm}{(\mathrm{CoFeCuZr})}_{z}$ magnets with much Fe.