${\mathrm{Sm}}_2{\mathrm{Fe}}_{17}$ has long been known as a potential high-performance magnet whose deficiencies—planar anisotropy and lower-than-optimal $T_c$—can be remedied by nitrogen addition, but which presents synthesis difficulties. Herein we apply first-principles calculations to search for alternative low-cost, high-performance permanent magnets in this family, by exploring simultaneous Fe and Al substitution. Specifically, the goal is to improve properties of ${\mathrm{Sm}}_2{\mathrm{Fe}}_{14}{\mathrm{Al}}_3$ easy-plane magnet at the stoichiometric composition. Density functional theory calculations were executed for three series of compounds, i.e., ${\mathrm{Sm}}_2{\left({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\right)}_{14}{\mathrm{Al}}_3$, ${\mathrm{Sm}}_2{\left({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\right)}_{15}{\mathrm{Al}}_2$, and ${\mathrm{Sm}}_2{\left({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\right)}_{16}\mathrm{Al}$. We find that substitution of Fe with 12–18 of Co in $\%{\mathrm{Sm}}_2{\mathrm{Fe}}_{14}{\mathrm{Al}}_3$ modifies the magnetic anisotropy type from easy plane to easy axis with a substantial anisotropy of 7.1 MJ/${\mathrm{m}}^3$. We also demonstrate that the largest part of magnetic anisotropy is introduced by $4f$ Sm atom electrons. Thus the rotation of magnetic moment orientation from $\langle 1\overline{1}0\rangle$ to $\langle 111\rangle$ is followed by an increase of the occupied $4f$ state number and, as a result, the orbital part of the magnetic moment of one of the Sm atoms. This increase of the occupied $4f$ state number at an energy $\sim -$4.3 eV results in a significant reduction of band structure energy. The substitution of Fe by Co does not significantly reduce the magnetization of the compound and keeps it slightly above 1 T. This combination of magnetic anisotropy and magnetization makes the compound a promising candidate for a permanent magnet.

• Received 13 January 2022
• Revised 5 April 2022
• Accepted 3 May 2022

DOI:https://doi.org/10.1103/PhysRevMaterials.6.054411