Site preference and magnetic properties of Zn-Sn-substituted strontium hexaferrite

The site preference and magnetic properties of Zn, Sn, and Zn-Sn substituted M-type strontium hexaferrite (SrFe12O19) have been investigated using first-principles total-energy calculations based on density-functional theory. The site occupancy of substituted atoms was estimated by calculating the substitution energies of different configurations. The distribution of different configurations during the annealing process at high temperature was determined using the formation probabilities of configurations to calculate magnetic properties of substituted strontium hexaferrite. We found that the magnetization and magnetocrystalline anisotropy are closely related to the distributions of Zn-Sn ions on the five Fe sites. Our calculation shows that in SrFe11.5Zn0.5O19, Zn atoms prefer to occupy 4f(1), 12k, and 2a sites with occupation probabilities of 78%, 19%, and 3%, respectively, while in SrFe11.5SnO19, Sn atoms occupy the 12k and 4f(2) sites with occupation probabilities of 54% and 46%, respectively. We also found that in SrFe11Zn0.5Sn0.5O19, (Zn, Sn) atom pairs prefer to occupy the (4f(1), 4f(2)), (4f(1), 12k), and (12k, 12k) sites with occupation probabilities of 82%, 8%, and 6%, respectively. Our calculation shows that the increase of magnetization and the reduction of magnetic anisotropy in Zn-Sn substituted M-type strontium hexaferrite as observed experimentally are due to the occupation of (Zn, Sn) pairs at the (4f(1), 4f(2)) sites. Published under license by AIP Publishing.