Effect of divalent cation substitution in the magnetoplumbite structured BaFe₁₂O₁₉ system

Synthesis of magnetically ordered barium hexaferrite powders and the adjustment of magnetic properties for perpendicular magnetic recording media are realized through substitution of divalent cation (Ca) in the BaFe₁₂O₁₉ system. The Ca²⁺ substituted Ba_1−xCa_xFe₁₂O₁₉ (where x = 0.05, 0.1, 0.15 and 0.2) compounds have been prepared through solid state reaction technique. The powder X-ray diffraction analysis reveals that all the prepared compounds crystallized in magnetoplumbite hexagonal structure and the flat hexagonal platelet morphology of the crystallites was identified through scanning electron microscopy. The formation of magnetoplumbite structured Ba_1−xCa_xFe₁₂O₁₉ system due to mechanical activation was supported by micro-Raman measurements. Both pure and Ca substituted BaFe₁₂O₁₉ compounds exhibit sharp intense peaks which reveals defect free environment in the crystal lattice. From the room temperature magnetization studies, it was observed that the saturation magnetization (M_S) and remanent magnetization (M_R) values drastically decreases for the Ba_0.95Ca_0.05Fe₁₂O₁₉ compound which may be due to the existence of spin canting effect and leads to the reduction of super exchange fields. The increase in M_S and M_R values for the Ba_0.9Ca_0.1Fe₁₂O₁₉ and Ba_0.85Ca_0.15Fe₁₂O₁₉ compounds could be attributed to the enhanced hyperfine fields at 12k and 2b sites due to the strengthening of Fe³⁺–O–Fe³⁺ super exchange interactions. A large reduction in the coercivity value from 3,090 to 1,548 Gauss may be attributed to the fall in magneto crystalline anisotropy. The high temperature magnetization studies infer that while increasing substitution level of Ca in the BaFe₁₂O₁₉ system results in decreasing trend in Curie temperature. The room temperature dielectric measurement shows that the incorporation of Ca²⁺ in the BaFe₁₂O₁₉ system results with increase in the dielectric constant and this case substantiates the space charge polarization. The magnetically ordered BaFe particulate having higher saturation and low coercivity values with superior magnetic and dielectric behaviour exhibiting the possibility for future high-recording-density storage products.