Magnetic properties of glass ceramics derived from glasses with composition 41CaO · (52-x)SiO2 · 4P₂O₅ · xFe₂O₃ · 3Na2O (2 £ x £ 10mol% iron oxide (Fe₂O₃)) are reported. Structural investigation revealed the presence of nanocrystalline magnetite phase in the heat-treated samples containing x³2 mol% Fe₂O₃. Magnetic hysteresis cycles of the glass-ceramic samples were obtained with a maximum applied field of ± 20 kOe as well as a low field of ± 500 Oe, in order to evaluate the potential of these glass ceramics for hyperthermia treatment of cancer. Samples with x>2 mol% of iron oxide exhibited magnetic behavior similar to soft magnetic materials with low coercivity. The evolution of magnetic properties in these samples as a function of iron oxide molar concentration is correlated
with the amount and crystallite size of magnetite phase present in them.