Structure, microstructure, and magnetism in ferrimagnetic bioceramics.

The structural and magnetic properties of ferrimagnetic bioglass ceramics in the system [0.45(CaO,P2O5)(0.52 - x)SiO2 xFe2O3 0.03Na2O], x = 0.05, 0.10, 0.15, 0.20 and heat-treated at the temperature range 600-1100 degrees C are assessed. The structure and microstructure of the samples are characterized with X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Calcium phosphate and magnetite develop as the two major crystalline phases. For x = 0.10 and 0.20, calcium phosphate undergoes a gradual transition from the monoclinic to the rhombohedral crystal system (SG P21/a-->R3c) as the heat-treatment temperature increases from 800 to 1100 degrees C. Dendrites of iron oxide with crystallites of various sizes are observed to form within a glassy matrix enriched in calcium, phosphorous, and silicon. Saturation magnetization, remanence, and coercivity are found from dc magnetic measurements. They vary with the specific processing parameters of the composites, and these are correlated with the observed structure and microstructure of the materials.