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

Abstract Ca- and La-substituted M-type Sr-hexaferrites with the formulae Sr 1-x Ca x Fe 12 O 19 , SrFe 12-x Ca x O 19 , Sr 1-x La x Fe 12 O 19 , and SrFe 12-x La x O 19 ( 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 Sr 1-x Ca x Fe 12 O 19 and x  ≥ 0.1 for SrFe 12-x Ca x O 19 samples. La substitution into the Sr site in the Sr 1-x La x Fe 12 O 19 samples ( x  ≥ 0.1) was effective in controlling grain growth in the samples. The saturation magnetization value decreased with increasing x in the SrFe 12-x Ca x O 19 , Sr 1-x La x Fe 12 O 19 , and SrFe 12-x La x O 19 samples, whereas it remained almost constant in the Sr 1-x Ca x Fe 12 O 19 samples.