Effect of annealing on the structure and magnetic properties of mechanically milled TiO2–Fe2O3 mixture

A mixture of Fe2O3 and TiO2 oxides has been mechanically milled to form TiFe2O4 spinel phase. X-ray diffraction (XRD) pattern of the as-milled mixture shows the presence of both Fe2O3 and TiO2 phases. The diffraction peaks become broader and their relative intensity drastically decreases due to the particle size reduction and accumulation of strains. The milled powder was then subjected to annealing at different temperatures (600, 750, 900, 1200 °C). Annealing at 600 °C and 750 °C does not show any significant change in the phase formation. Nonetheless, XRD patterns show a narrowing and an increase in the intensity of Fe2O3 peaks with respect to TiO2, which was reflected by an evolution in particle nano-structure following SEM analysis. An increase in the intensity ratio of the major peaks belonging to Fe2O3 relative to the as-milled mixture, which was associated with a reduction of the amount of TiO2, suggested a possible insertion of Ti into the Fe2O3 crystal lattice. However, in VSM measurements, annealing at 600 °C and 750 °C does not change the ferromagnetic phase but the effect of annealing was a notable reduction in the values of both Ms and Mr (saturation magnetization and remanence magnetization respectively) Ultimately, as the powder was heated to 900 °C a new phase seemed to have emerged, this phase was confirmed by SEM, XRD, and magnetic measurements (VSM) where it change phase from ferromagnetic to paramagnetic phase.