Variability of structural and magnetic properties of nanocrystalline spinel ferrites

Abstract

Nanocrystalline spinel ferrites, with the general formula MFe2O4 (M is a divalent cation) are an important class of nanostructured materials with their potential in ceramic, electrochemical, magnetic, ferroelectric, catalytic and biomedical applications. Using a low temperature synthesis of such materials it is possible to obtain ultra fine particles. The crystal structure, microstructure and magnetic properties of series of nanocrystalline spinel ferrites have been studied by XRD, HRTEM, Mössbauer spectroscopy and SQUID measurements. The Rietveld analysis of the powder diffraction data have been performed (using Fullprof software) to obtain quantitative microstructural information (e.g. the cation distribution, the crystallite size, microstrain). More sophisticated models have been used to explain magnetic behavior of an assembly of nanostructured particles, which include microscopic mechanisms such as spin disorder, surface contributions and the presence of interparticle interactions (exchange and/or dipolar). The saturation magnetization of investigated nanostructural vs. bulk spinel ferrites is discussed in term of a competition between the site exchange of cations and the spin canting phenomena. For a selected example, the variation in the particle anisotropy energy, extracted from the magnetic measurements in high and low external magnetic field, is well describe accounting for the interparticle interaction and the surface effects on the energy barrier.