Magnetic Behavior and Microstructure of Vanadium Phosphate Glasses

The magnetic properties and microstructures of the vanadium phosphate glass system over the composition range 60 to 90 mol% V₂O₅ were investigated to study magnetic ordering in the glass and the effect of microstructure on its magnetic properties. Direct antiferromagnetic coupling between V⁴⁺ ions in the glassy matrix exists, and a transition temperature near - 70°C was observed. As-cast glasses with high V₂O₅ concentrations separated into two glassy phases; this separation increased the ESR line width as a result of inhomogeneity broadening. The separation, which concentrated the vanadium ions in a vanadium-rich phase, caused a hysteresis in the plot of ESR line intensity vs temperature at the transition temperature. Reduction of the vanadium ions by dextrose added to the melt enhanced phase separation and resulted in weak antiferromagnetic transitions at +70° and -120°C, the Neel temperatures of VO₂ and V₂O₃, respectively.