Estudo das propriedades estruturais locais de fluidos magnéticos : da nanopartícula à dispersão

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Local structural properties of magnetic fluids based on nanosized particles of zinc, copper or nickel ferrite are investigated. Nanograins prepared by a soft chemistry method are dispersed in acidic medium thanks to a core-shell strategy that prevents the particles from dissolution. Their chemical composition is no longer homogeneous and they can be described as a core of stoechiometric ferrite surrounded by a surface layer with an average composition of Fe3O4 type. Chemical titrations and X-ray Absorption Spectroscopy are used to quantitatively investigate the coordination shells of metallic cations. The core-shell model is confirmed with a ferrite core with cation inversion at A- and B-site of the spinel nanocrystal and effects related to spatial confinement at nanoscale. Rietveld refinement of the x-ray diffractograms patterns, carried out within the core-shell model using two spinel phases, suggests that the nanoparticle density tend to the bulk value when the particle size increases, indicating smaller surface contribution. Small Angle Neutron Scattering, used to characterize the colloidal structure of the solution, shows that a magnetic field induces an anisotropy inside the solution. Finally, a chemical, structural and magnetic characterization of ferrofluids based on rare earth doped maghemite nanoparticles, precursor material for nanoradiotherapy, is presented and discussed.

ASSUNTO(S)

difração de raios x fisica da materia condensada nanopartículas magnéticos absorção de raios x fluídos magnéticos

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