Preparation and Characterization of Superparamagnetic Nanocrystalline Cobalt Ferrite Materials

A series of cobalt ferrite (CoxFe3-xO4) nanocrystalline particles with different compositions and grain size were prepared by a chemical route, and the superparamagnetic properties of the powders obtained are discussed. The nanoparticles were prepared at fairly low temperature by precipitation using Fe(NO3)6.9H2O and Co(NO3)2.6H2O as raw materials. The morphology and crystal structure of the particles were studied by TEM and XRD. Mossbauer spectra were obtained at room temperature, and could be satisfactorily resolved into the central doublet superimposed on a distinct sextet pattern, indicating the existence of superparamagnetic particles. It was shown that the fraction of superparamagnetic particles increases with decreasing particle size. This size effect is discussed. 16 refs