Formation Study of Nanocomposite Thin Films of Ferrite Dispersed in a Silica Matrix Prepared by sol-Gel Process
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Formation Study of Nanocomposite Thin Films of Ferrite Dispersed in a Silica Matrix Prepared by sol-Gel Process
Nelcy D. S. Mohallem and Luciana M. Seara Laboratório de Materiais - Department of Chemistry, ICEx, Federal University of Minas Gerais 31270-901 Belo Horizonte, MG, Brasil [email protected]
ABSTRACT Magnetic nanocomposite thin films formed by cobalt ferrite dispersed in silica matrix were prepared by sol-gel process using tetraethylorthosilicate (TEOS) as a precursor of silica, and metallic nitrates as precursors of the ferrite. The films were prepared with 5-50 wt. % ferrite contents and deposited on substrate using the dip-coating process. The films obtained were adherent, transparent, homogeneous and free of microcracks, with thickness between 30 and 500 nm. The films obtained presented crystalline CoFe2O4 phases dispersed in SiO2 amorphous matrix and saturation magnetization of approximately 9 emu/g considering the composite mass and 30 emu/g considering the ferrite mass.
INTRODUCTION Composite materials formed by nanoparticles dispersed in inert matrices have important application in areas such as catalysis and electronics due to the possibility to develop more active catalysts and new optical or optic-magnetic devices [1,2]. The interest in the magnetic nanocomposites [3-5] has increased in the last years due to the properties presented by these materials, which depend of particle sizes and of their distribution in the matrix. These systems present different properties from those of bulk materials, such as the superparamagnetism of magnetic oxide nanoparticles and the increase in saturation magnetization. Sol-gel process has been used to prepare ultra-fine particles dispersed in different bulk matrixes and, particularly to produce some kinds of transparent oxide thin films. This process facilitates the monitoring of film preparation parameters, making it possible a good control of the chemical composition and morphology [4-9] of the material. The objective of this work is to describe the preparation of magnetic nanocomposite thin films of cobalt ferrite dispersed in a silica matrix by sol-gel process. We have investigated the best deposition parameters to obtain transparent and homogeneous magnetic films.
EXPERIMENTAL Magnetic composite thin films of crystalline cobalt ferrite dispersed in a silica matrix were prepared by sol-gel process using tetraethylorthosilicate (TEOS) as a precursor of silica, and ferric nitrate and cobalt nitrate as precursors of the ferrite. The films were prepared with 5 – 30 wt. % of ferrite dispersed in the silica matrix. The precursor solution was kept under agitation at room temperature for one hour, and rested until the viscosity reached the best value
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condition, between 2 and 5 cp. The films were prepared in
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