First principles study of Al substituted strontium hexaferrite

We have studied the site occupancy and magnetic properties of Al substituted M-type Strontium hexaferrite, SrFe$_{12-x}$Al$_{x}$O$_{19}$ with x $=$ 0.5 and x $=$ 1.0 using density functional theory (DFT). For x $=$ 0.5 case, an Al atom preferentially occupy the 2a site at T $=$ 0 K, this trend endures up to 220 K beyond this temperature Al atom is more likely to occupy the 12k site. For the x $=$ 1.0 case, the site preference probability is maximum when two Al atoms occupy the 2a and the 12k sites. We found that magnetic anisotropy of SrFe12-xAlxO19 increases as the concentration of Al atoms increases, while there is a reduction in the magnetic moment per unit cell by 5$\mu $B and 10$\mu $B in the case of x $=$ 0.5 and x $=$ 1.0, respectively. Our results agree with the available experimental results on Al substituted strontium hexaferrite.