Preparation of Magnetite (Fe3O4) with Non-Stoichiometric Ratio and its Effect on Raman Spectroscopy in the Presence of Magnetic Field

Fe3O4 nanoparticles were fabricated by co-precipitation method with stoichiometric and non-stoichiometric ratios in air atmosphere and temperature of 78 °C. Structural analysis of the samples was performed by X-ray diffraction pattern (XRD). The magnetic properties of the nanoparticles were investigated using an alternating force gradient magnetometer (AGFM) and Faraday scale. The XRD patterns indicated that the specimens were single phase and the cubic phase of the magnetic spinel was formed. The diffraction peaks of the XRD pattern are consistent with the reference card 0866-088-01 for the magnetite phase. For non-stoichiometric ratios,  by increasing Fe2+/Fe3+, the Cure temperature decreases compare to the bulk sample (585 °C), due to the decrease in particle size. As the particle size decreases, the number of super-exchange interactions between the sites of the spinel crystal structure decreases. Therefore, by increasing the ratio of divalent iron cation to its trivalent cation, nanoparticles with saturated magnetism and similar coercive force and different Curie temperature can be produced and with less heat energy, the order of the spins is disturbed and the transition from the ferromagnetic phase to the paramagnetic phase occurs. The Raman spectra for the  samples showed specific peaks related to the magnetite structure at 336 cm-1 and 490 cm-1 wave number. Comparison of the Raman spectroscopy of the samples after applying the magnetic field indicated an increase in the number and height of the peaks, which was due to the orientation of the nanoparticles in the direction of the magnetic field.