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

• Published in: Journal of magnetism and magnetic materials 2017-07, Vol.433, p.29-34
• Main Authors: Bhandare, S.V., Kumar, R., Anupama, A.V., Choudhary, H.K., Jali, V.M., Sahoo, B.
• Format: Article
• Language: English
• Subjects: Annealing; Citric acid; Combustion; Electron micrographs; Ferric nitrate; Ferrites; Lattice parameters; Magnetic properties; Manganese; Manganese ferrite; Nanoparticles; Oxidation; Sol-gel auto-combustion method; Sol-gel processes; Spinel; Studies; Superparamagnetism; Temperature
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2017.02.040

•Phase pure MnFe2O4 samples were prepared by sol-gel auto-combustion method.•Annealing MnFe2O4 below ∼500°C, two spinel phases were observed indicating partial oxidation of Mn2+ to Mn3+.•Oxidation of Mn2+ to Mn3+ results in decrease in lattice parameter of the spinel lattice.•Annealing at ≥ 600°C, MnFe2O4 decomposes into crystalline α-Mn2O3 and α-Fe2O3 along with amorphous-FeO phase. 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 2h 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.