Structural phase transformation of as-prepared Mg–Mn nanoferrites by annealing temperature

Abstract

As-prepared Mg0.2Mn0.8Fe2O4 nanoferrite samples by coprecipitation method were annealed at different temperatures T. XRD, TEM, IR, VSM and Mössbauer techniques were used to characterize the samples. This study proved the transformation of the sample structure from cubic spinel to Z-type hexagonal phase at 700°C. This transformation was assigned to Jahn–Teller effect of the Mn3+ and Fe2+ ions and/or atomic disorder in the crystal lattice. All the deduced structural parameters were affected by the transformation process. The infrared and structural parameters showed dependence on T, whereas tetrahedral band position did not. TEM images showed agglomeration of the nanoparticles, where the average particle size ranged 25–55nm and was a little higher than R. Study on the elastic properties proved the weakening of inter-atomic bonds inside the crystal lattice as T increases. The magnetic properties were affected by the transformation process and showed T dependence, whereas Ms and Hc proved dependence on porosity. Hyperfine interaction parameters, area ratio (B/A) and spontaneous magnetization were discussed as functions of T.