Crystallization process and magnetic properties of amorphous iron oxide nanoparticles

This paper studied the crystallization process, phase transition and magnetic properties of amorphous iron oxide nanoparticles prepared by the microwave heating technique. Thermal analysis and magnetodynamics studies revealed many interesting aspects of the amorphous iron oxide nanoparticles. The as-prepared sample was amorphous. Crystallization of the maghemite γ-Fe₂O₃ (with an activation energy of 0.71 eV) and the hematite α-Fe₂O₃ (with an activation energy of 0.97 eV) phase occurred at around 300 °C and 350 °C, respectively. A transition from the maghemite to the hematite occurred at 500 °C with an activation energy of 1.32 eV. A study of the temperature dependence of magnetization supported the crystallization and the phase transformation. Raman shift at 660 cm^-1 and absorption band in the infrared spectra at 690 cm^-1 showed the presence of disorder in the hematite phase on the nanoscale which is supposed to be the origin of the ferromagnetic behaviour of that antiferromagnetic phase.