Formation of submicron-sized SrFe12−xAlxO19 with very high coercivity

Submicron-sized SrFe12−xAlxO19 (x=1.3) was formed in glass-ceramic matrix using controlled thermocrystallization of the SrO–Fe2O3–Al2O3–B2O3 glass and the hexaferrite powder was obtained by removing the matrix phases. The samples were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray (EDX) analysis and magnetization measurements. The glass-ceramic material exhibits very high coercivity value up to 10.18 kOe which approaches a theoretically estimated maximum value for the compound. The hexaferrite powder consists of well faceted single crystals, which adopt the shape of a truncated hexagonal bipyramid. The powder saturation magnetization value is close to the theoretically estimated one for bulk material. Crystal structure of the powder was refined by Rietveld method and distribution of Al atoms on Fe sites was determined. Al atoms occupy 41% of 2a sites, 14% of 12k sites and 5% of 4e(1/2) sites, while 4f sites are not affected.