Effect of melt atmosphere on the magnetic properties of a [(SiO ₂)₄₅(CaO)₅₅]₆₅[Fe₂O ₃]₃₅ glass

Mossbauer and magnetization measurements have been made on a [(SiO ₂)₄₅(Ca0)₅₅]₆₅[Fe₂O ₃]₃₅ glass equilibrated at 1550°C in a variable oxygen partial pressure atmosphere. The concentration of Fe²⁺ cations, as determined by Mossbauer analysis, is observed to increase with lower p _O2 pressures at the expense of the fraction of Fe³⁺ cations tetrahedrally coordinated. The Fe²⁺ doublet is found to display the largest isomer shift and quadrupole splitting. For the two types of ferric cations there appears to be a general tendency for the Fe³⁺ cations with lower coordination to have a lower isomer shift but a substantially larger quadrupole splitting. Room temperature magnetization data indicate all the samples to contain superparamagnetic particles which increase in abundance with lower p_O2 pressures. The superparamagnetic behavior is attributed to the formation of ferrite precipitates which occur during quenching.