Annealing temperature dependent structural and magnetic properties of MnFe2O4 nanoparticles grown by sol-gel auto-combustion method

Manganese ferrite (MnFe2O4) nanoparticles were synthesized by sol-gel auto-combustion method using manganese nitrate and ferric nitrate as precursors and citric acid as a fuel. Scanning electron micrographs show irregularly shaped morphology of the particles. The as-prepared samples were annealed at 400, 500, 600 and 800 °C for 2 h in air. The phase identification and structural characterizations were performed using powder X-ray diffraction technique along with Mössbauer spectroscopy. Magnetization loops and 57Fe Mössbauer spectra were measured at RT. After annealing the sample at or below ∼ 500 °C, we observed two different spinel phases corresponding to two different lattice parameters. This is originating due to the partial oxidation of Mn2+ to Mn3+. At high annealing temperatures (∼ 600 °C or above) the spinel MnFe2O4 phase decomposes into crystalline α-Mn2O3 and α-Fe2O3 phases, and amorphous FeO phase.