Theory of magnetic enhancement in strontium hexaferrite through Zn–Sn pair substitution

• The site preference and magnetic properties of Zn–Sn substituted M-type Strontium hexaferrite were investigated.
• Based on total energy calculations, we conclude that Zn and Sn ions preferentially occupy 4f1 and 4f2 sites, respectively.
• This is different from the previously suggested model where Zn and Sn ions occupy 2b and 4f sites, respectively.
• Our model predicts an increase of saturation magnetization as well as a decrease in magnetic anisotropy energy consistent with experiment.

We study the site occupancy and magnetic properties of Zn–Sn substituted M-type Sr-hexaferrite SrFe12−x(Zn0.5Sn0.5)xO19 with x=1 using first-principles total-energy calculations. We find that in the lowest-energy configuration Zn2+ and Sn4+ ions preferentially occupy the 4f1 and 4f2 sites, respectively, in contrast to the model previously suggested by Ghasemi et al. [J. Appl. Phys, 107, 09A734 (2010)], where Zn2+ and Sn4+ ions occupy the 2b and 4f2 sites. Density-functional theory calculations show that our model has a lower total energy by more than 0.2 eV per unit cell compared to Ghasemi's model. More importantly, the latter does not show an increase in saturation magnetization (Ms) compared to the pure M-type Sr-hexaferrite, in disagreement with the experiment. On the other hand, our model correctly predicts a rapid increase in Ms as well as a decrease in magnetic anisotropy compared to the pure M-type Sr-hexaferrite, consistent with experimental measurements.