MAGNETIC-PROPERTIES AND DISTRIBUTION OF CA IONS IN CA-SUBSTITUTED BA FERRITE

Results are reported on the solid state reaction of the system BaO-CaO-Fe2O3 at 1200-degrees-C. Magnetometry, x-ray diffractometry, and the analysis of chemical equilibrium equations have been used to study how Ca2+ enters the hexaferrite cell. For nominal compositions given by (1.01 BaO + 6 Fe2O3 + x CaO) evidence is obtained of the occupation by Ca2+ of Fe3+ sites. The solubility limit in this type of substitution is established at 0.26 Ca atoms per formula unit. The limiting phase has a saturation magnetization of 68.0 EMU g-1, as corresponds to a collinear spin structure. For nominal compositions (1.01 CaO + 6 Fe2O3 + z BaO) there is also substitution of Ca for Ba, with a substitution ratio (CaO/BaO) of 8/5. The saturation magnetization is low (64.9 EMU g-1) and would correspond to a non-collinear spin structure.