Synthesis, structural and magnetic characterization of nanocrystalline nickel ferrite-NiFe2O4 obtained by reactive milling

Nanocrystalline nickel ferrite (NiFe2O4) has been synthesized from a stoichiometric mixture of oxides NiO and alpha-Fe2O3 in a high energy planetary mill. An annealing at 350 degrees C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 +/- 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure. (C) 2011 Elsevier B.V. All rights reserved.