Preparation of magnetic glass-ceramics through glass crystallization in the Na2O-SrO-Fe2O3-B2O3 system

Glasses with the nominal compositions SrFe₁₂O₁₉ + nNa₂Sr₂B₄O₉ (n = 4, 6, 8, 10) and SrFe₁₂O₁₉ + 6Na₂Sr₃B₄O₁₀ were prepared via rapid quenching of oxide melts and were then heat-treated between 500 and 800°C in order to produce glass-ceramics containing fine SrFe₁₂O₁₉ particles. The materials were characterized by x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. The crystallization behavior of the glasses was investigated. The coercivity of the glass-ceramics was shown to increase with heat-treatment temperature, up to 486 kA/m. By dissolving the nonmagnetic matrix of the glass-ceramics with the nominal compositions SrFe₁₂O₁₉ + 6Na₂Sr₃B₄O₁₀ and SrFe₁₂O₁₉ + 4Na₂Sr₂B₄O₉, submicron-sized strontium hexaferrite particles were obtained.