The Study Of NiCuZn Ferrite Prepared By Sol-gel Method

The ferrite has been studied for a very long period of history since been found. It mainly consists of soft magnetic materials, gyromagnetic materials, piezomagnetic materials and so on. NiCuZn ferrtie has many advanteges, such as low eddy current losse, low cost, high resistivity. Its applicable frequency ranges from KHz to GHz, which helps to realize energy conversion and impedance switching of RF signal. It is mainly used in the manufacture of inductors and other components for many fields, such as computer, television and communication. However, few reports about the applications of NiCuZn ferrite thin films in high-frequency integrated circuits have been appeared by now. Very important factors lie in high saturation magnetization and low coercivity.In this thesis, Ni(NO3)2.6H2O,Cu(NO3)2.3H2O,(CH3COO)2Zn.2H2O and Fe(NO3)3.9H2O are used as raw materials, which are dissolved in dimethylformamid. Polyvinglpyrrolidone was added as a kind of surfactant. First NiCuZn gel was obtained using sol-gel method, then NiCuZn powder was gained by self-propagating combustion process and pressed to ring. NiCuZn film was prepared using spin coating method. The thesis focuses on the effects of iron content and heat treatment temperature on the properties of NiCuZn ferrite material. Some significant results have been obtained.1. Powder samples①Ni0.4Cu0.2Zn0.4FexO4powder materials prepared by sol-gel method form pure spinel phase when the heat treatment temperature exceeds750℃.②The presintering powder with better magnetic properties was obtained when the samples were presintered at1000℃for3hours and the content of Fe (x) was2.0. The coercivity is about8.4Oe, and the saturation magnetization is78.0emu/g.2.Sintering samples①The powder with better magnetic properties was obtained when the samples were sintered at1000℃and the content of Fe (x) was2.0. The coercivity is about1.5Oe, and the saturation magnetization is79.5emu/g.②When x is1.8and the sintering temperature is1000℃, the initial permeability of material is the highest, close to125, and the roll-off frequency is about20MHz. As x increases, the initial permeability decreases, but the roll-off frequency of sample increases. When x=2.1and2.2, the roll-off frequency is bigger than100MHz.2. Film samples①Film samples with different Fe content all form pure spinel phase when they were heat-treated at800℃for6minutes. Although the Fe content changes, the peak position and peak intensity of the film samples keep the same.②The crystalline grain size of fim samples with different Fe content is about40-90nm when they were heat-treated at800℃for6minutes. And as the Fe content increases, the crystalline grain size first decreases then increases.③Film with better magnetic properties was obtained when the value of x was2.0. The coercivity is about63.7Oe, and the saturation magnetization is403.0emu/cc. Furthermore, the film samples with less or more Fe content have higher coercivity and lower saturation magnetization.④As the Fe content changes, the variation trend of magnetic properties of sintering samples and film samples keeps the same. However, the coercivity of film samples increases a lot, which is due to stress brought by the different thermal expansion coefficient of NiCuZn film and Si substrate.