Effect of Ca and La substitution on the structure and magnetic properties of M-type Sr-hexaferrites

Ca- and La-substituted M-type Sr-hexaferrites with the formulae Sr1-xCaxFe12O19, SrFe12-xCaxO19, Sr1-xLaxFe12O19, and SrFe12-xLaxO19 (x = 0, 0.1, 0.2, 0.3, and 0.4) were prepared by conventional solid-state reaction routes. Based on the changes in the lattice parameter with different x, it can be concluded that Ca substitutes into both Sr and Fe sites, whereas La substitutes only into the Sr site in the M-type hexaferrite structure. Ca substitution promotes the densification of the hexaferrites with the growth of large grains at the doping level of x ≥ 0.3 for Sr1-xCaxFe12O19 and x ≥ 0.1 for SrFe12-xCaxO19 samples. La substitution into the Sr site in the Sr1-xLaxFe12O19 samples (x ≥ 0.1) was effective in controlling grain growth in the samples. The saturation magnetization value decreased with increasing x in the SrFe12-xCaxO19, Sr1-xLaxFe12O19, and SrFe12-xLaxO19 samples, whereas it remained almost constant in the Sr1-xCaxFe12O19 samples.