Preparation And Magnetic Properties Of Rare Earth Modified Cobalt And Nickel Ferrite Nanoparticles

Scientists have been devoting to enhance the density of magnetic recording media for years. Magnetic materials are expected to be with high coercivity and high saturation magnetization. In this thesis, cobalt, nickel and rare earth elements are doped into ferrite and their effects on magnetic performance of ferrite are studied.Ferrite nano particles doped with cobalt, nickel and rare earth elements are prepared by hydrothermal, solvent-thermal and sol-gel method. According to the sample prepared by hydrothermal method, the doping cations can enter the spinel lattice. Rare earth cations mostly occupy position B because of their big radius. Cerium are oxidized to Ce4+, whose radius is relatively small, and Ce4+ mostly occupies position A. As a whole, the coercivity of cobalt ferrite doped with rare earth element is bigger than that of pure cobalt ferrite. The coercivity of ferrite containing cobalt is bigger than that of ferrite containing nickel because of special physical properties of cobalt. Among all the samples, one sample shows outstanding magnetic properties as the shape anisotropy of the sample plays an important role on the magnetic properties. The cerium in the sample prepared by solvent-thermal method exists as Ce3+, and it mostly occupies position B of spinel. The size of the particles prepared by sol-gel method is little bigger than critical dimension and accordingly these samples have relatively high coercivity.Acicular α-Fe2O3 and α?FeOOH nano particles are prepared by hydrolytic method and α?FeOOH with good axial ratio is prepared by microwave-induced method, then 30% cobalt is doped into this α?FeOOH sample. Ideal acicular ferrite samples have been prepared and the formation mechanism has also been studied.The adsorption behavior of organic molecules on the surface of iron and iron oxide has been studied by Raman spectroscopy. When the organic molecules adsorb on the surface of iron oxide, they only adsorb on iron element in stead of oxygen element. This means the mechanism of the effect of shape-controller on the growth process of nano-particles can be studied by Raman spectroscopy in the future.