Magnetic and microstructural studies of Ca-hexaferrite based glass-ceramics

Abstract

X-ray diffraction, magnetisation and EPR measurements have been carried out on the glass-ceramic specimens of CaO---Fe₂O₃---B₂O₃ based glass systems. The results are explained on the basis of their microstructures. In a system, 13CaO---48Fe₂O₃---39B₂O₃, CaFe₂O₄ is found to crystallise as a magnetic phase having a surprisingly large magnetisation (85 emu/g). The actual composition of this phase is believed to be Ca_0.6Fe_2.4O₄ with Fe²⁺ and Fe³⁺ ions distributed among the different available sites in a particular way. CaFe₁₂O₁₉ and Ca₃Fe₁₅O₂₅ ferrites can be crystallised with useful magnetic properties in the systems containing (1 mol%) Ag₂O or P₂O₅ as nucleating agent. Incorporation of As₂O₃ (0.1 mol%) in the P₂O₅ system gives rise to the crystallisation of Ca₃Fe₁₅O₂₅ particles in platelet shape with an aspect ratio ~12. The crystallisation behaviour and microstructural features of the systems are consistent with the EPR linewidths and g-values.