Preparation Of CoFe₂O₄/SiO₂Composite Thin Films By Sol-Gel Method And Characterization Of Magnetic Properties

In this thesis, CoFe2O4nano-powder,(CoFe2O4)x/(SiO2)1-x and CoFe2-xCexO4/SiO2composite thin films were prepared by Sol-Gel method using nitrate as initial material. The complexation effect of different complexing agent for CoFe204nano-powder were studied by contrast experiments; the influences of SiO2on the average grain size of CoFe2O4nano-powder and the magnetic properties of (CoFe2O4)x/(SiO2)1-x composite thin films were investigated; the influence of the quantity of Fe3+substituted by Ce3+on the magnetic properties of CoFe2-xCexO4/SiO2thin films was studied. The main contents of this thesis are as follows:Pure CoFe2O4nano-powder was prepared by Sol-Gel method. Experiments using nitrate as initial materials and ethylene glycol monomethylether as solvent were performed, in order to study the crystallization propertities of CoFe2O4with nitric acid, citric acid, acetic acid as different complexing agents and without any complexing agent. The result shows that acetic acid is the best complexing agent. In this experiment, the influences of acetic acid quantity and annealing temperature on the crystallization propertities of CoFe2O4were studied.(CoFe2O4)x/(SiO2)1-x thin films were prepared with the same method that pure CoFe2O4nano-powder was prepared with. The average grain size of CoFe2O4nano-powder can change from5.0nm to40.5nm by adjusting the x value. Magnetic properties with diferent x values were ascertained by VSM. Saturation magnetization and remanent magnetization become higher when x value grows larger. When x value keeps growing, Coercivity increases firstly, then decreases, and then increases again. CoFe2O4is not uniformly distributed but descends from inside to outside of thin film, which determined by EDS. The surface roughness of thin film is9.8nm, which is determined by AFM.The CoFe2-xCexO4/SiO2composite thin films were prepared. The research shows that spinel structure can be maintained when0.10<x<0.15. Only CeO2single sundry appear when we increase the substitution quantity. When x=0.1, the thin film has a relatively high coercivity (82.70koe), highest saturation magnetization (106.514emu/cm3) and highest remanent magnetization (37.367emu/cm3). which is determined by VSM.