Studies Of Nicuzn Ferrite Powders And Films Prepared By Sol-gel Method

NiCuZn ferrites are excellent soft magnetic materials in high-frequency devices due to their low cost, high resistivity and low eddy current losses, and it is applied in the frequency rang from kHz to a few GHz, wider than MnZn (less than 1MHz)and NiZn(1-100MHz) ferrite materials. NiCuZn ferrites have been studied extensively for multilayer chip inductor applications for it can realize energy conversion and impedance switching of RF signal in wide band, which widely used in the field of PC, TV, electronic device etc. But up to now, the applications of NiCuZn ferrite thin films in high-frequency integrated circuits have been reported scarcely. The successful growth of high saturation magnetization Ms and low coercivity Hc magnetic thin film is an important step towards their future incorporation. For preparing films, RF magnetic alternative sputtering and vacuum evaporation are always used. But films prepared by RF magnetic alternative sputtering have the problem that composition drift due to the sputtering speed of ions are different, also vacuum evaporation have bad adhesive quality, repeatability error, and can not preparing ferrite films because it high melting point. Using sol-gel spin coating method preparing ferrite film has not been studied very much. The sol-gel method is a wet-chemical technique which is widely used in the fields of material science and ceramic engineering since it can realize molecular level mixing. Thus it is a low temperature technique that allows for the fine control of the product's chemical composition. The precursor sol can be deposited on a substrate, or cast into a suitable container with the desired shape to form a film. In this study, sol-gel processing was used to prepare NiCuZn ferrite powders and films. Raw materials first dissolved in dimethylformamide, and then polyvinglpyrrolidone was added as a kind of surfactant. The effects of raw material composition and the calcinate temperature on magnetic properties of powders and films were investigated in order to prepare high performance NiCuZn films in the future.1. Igniting stable gels in clean glass dishes, fluffy precursor powders were obtained. It can be seen from the XRD patterns when the temperature exceeds 750℃,α-Fe2O3 phase disappears and single phase of spinel NiCuZn ferrite develops. But films with same composition at 400℃for 30 min, no spinel ferrite can be obtained. When the temperature is up to 600℃, the single spinel ferrite phase is achieved.2. Powders obtained from Ni0.4Cu0.2Zn0.4Fe1.9O4 gel have better magnetic properties than those from gels with other composition. After heat-treating at 900℃for 3 h, coercivity Hc and saturation magnetization Ms are 9 Oe and 72.4 emu/g. When the temperature is up to 1000℃, the Hc is 5 Oe and Ms reaches 73.6 emu/g.3. Adding acetic to adjust pH value of sol to 3.2, coercivity Hc of films on Si substrates will be smaller than those from sols with other condition, indicating that pH=3.2 can enhance activity of the reactant.4. Aging sols at different temperature, the results showed that Hc decreases first with the increase of sols aging time and then become stable. The film from gel formed at room temperature has lower Hc values and becomes stable firstly.5. Different from the powders, NiCuZn films produced on Si (100) from the Ni0.4Cu0.2Zn0.4Fe2O4 gel possess high properties. When heat-treating condition is around 600℃for 6 min, samples with low Hc and high Ms were obtained. The minimal Hc is 16 Oe and Ms is about 300 emu/cm3. Comparing to the films with long-time heat treating, the films prepared with short heat-treating time exhibits better soft magnetic properties.6. Measuring Electron Spin Resonance (ESR) of NiCuZn ferrite powders and films which heat-treated at relative high temperature, g factor which calculate from the EPS spectrum will be change. The reason maybe lay in the fact that polyvinglyrrolidone can improve the activity of reactants by sol-gel, so Zn ions which occupy A coordination lattice will be volatilized at relative high temperature, other ions replace can leading molecular magnetic moment change.