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تسجيل مستخدم جديدCorrelation between site preference and magnetic properties of Zn-Sn-substituted strontium hexaferrite
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The site preference and magnetic properties of Zn, Sn and Zn-Sn substituted M-type strontium hexaferrite (SrFe$_{12}$O$_{19}$) have been investigated using first-principles total energy calculations based on density functional theory. The site occupancy of substituted atoms were 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 show that in SrFe$_{11.5}$Zn$_{0.5}$O$_{19}$, Zn atoms prefer to occupy $4f_1$, $12k$, and $2a$ sites with occupation probability of 78%, 19% and 3%, respectively, while in SrFe$_{11.5}$SnO$_{19}$, Sn atoms occupy the $12k$ and $4f_2$ sites with occupation probability of 54% and 46%, respectively. We also found that in SrFe$_{11}$Zn$_{0.5}$Sn$_{0.5}$O$_{19}$, (Zn,Sn) atom pairs prefer to occupy the ($4f_1$, $4f_2$), ($4f_1$, $12k$) and ($12k$, $12k$) sites with occupation probability 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 is due to the occupation of (Zn,Sn) pairs at the ($4f_1$, $4f_2$) sites.
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We study the site occupancy and magnetic properties of Zn-Sn substituted M-type Sr-hexaferrite SrFe$_{12-x}$(Zn$_{0.5}$Sn$_{0.5}$)$_x$O$_{19}$ with x = 1 using first-principles total-energy calculations. We find that in a ground-state configuration Z
n-Sn ions preferentially occupy $4f_1$ and $4f_2$ sites unlike the model previously suggested by Ghasemi et al. [J. Appl. Phys, textbf{107}, 09A734 (2010)], where Zn$^{2+}$ and Sn$^{4+}$ ions occupy the $2b$ and $4f_2$ 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 Ghasemis model. More importantly, the latter does not show an increase in saturation magnetization ($M_s$) 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 $M_s$ as well as a decrease in magnetic anisotropy compared to the pure $M$-type Sr-hexaferrite, consistent with experimental measurements.
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