Magnetic glass-ceramics with hexagonal lead ferrites

Abstract

The crystallisation process of the different magnetic phases has been studied by suitable heat treatments of an initial glass composition of 50 PbO-20Fe₂O₃-30B₂O₃ (mol%). The nucleation and growth times have been varied to find out the optimum condition for crystallisation of the hexaferrite phases. The hexagonal lead ferrites PbFe₁₂O₁₉ and Pb₅Fc₁₄O₂₆ respectively can be precipitated as the major crystalline phase in most of the samples. A maximum of ~ 60 vol.% crystallisation is achieved for the Pb₅Fe₁₄O₂₆ ferrite phase. It also exhibits the highest coercivity ( ~3000 Oe) and magnetic moment ( ~22 emu/g). The crystallised volume fraction, microstructure and other magnetic properties are strongly dependent on the heat-treatment schedule. The presence of magnetic field has been observed to improve the crystallisation process of the ferrite glass ceramics. The magnetic and EPR data have been found to be consistent with optical and electron micrographs which show a wide spectrum of particle sizes of the precipitated magnetic particles.