Sol-gel Preparation Of Nizn Ferrite Thin-film Technology

In this dissertation, for the purpose of enlarging saturation magnetization and reducing coercivity of NiZn ferrite thin films, the effect of process parameters, doping and underlayer on the proerties of NiZn ferrite thin films prepared by sol-gel method were investigated.Based on the formulation of Ni_0.5Zn_0.5Fe₂O₄, to realize the object of high saturation magnetization and low coercibity NiZn ferrite thin films, the effects of sol preparation, spin-coating process, annealing process parameters, Ti-substitution, Sn-substitution and ZnFe₂O₄ underlayer on the microstructure and magnetic properties of NiZn ferrite thin films were investigated. Research on the crystallization process of the dried gel by DSC-TG reveals that it starts to crystal at 560℃. In the process of sol preparation, select appropriate sol concentration, stirring temperature and still time can get uniform and stable sol, which is the key of the sol-gel process. The addition of PEG can improve the distribution of metal ions which makes them distribute evenly, and then improve the films performance. Spin-coating process directly affects the uniformity and the thickness of the fims, further affects the properties of the films. Select proper spin speed, spin time, coating thickness and substrate whose lattice constant and thermal expansion coefficient close to the films can reduce internal stress and improve films properties. Heating rate directly affects the number of nucleation, and the annealing temperature and annealing time determine the crystallization extent and grain sizes, and low quenching temperature is conducive to reduce the stress within the films. Reasonable annealing process is that keep 2℃/ min heating rate to 700℃and anneal the films at 700℃for one hour then cool to room temperature in the furnace. The addition of non-magnetic ions Ti4+ and Sn⁴⁺ decreases the A-B superexchange interaction and the net overall magnetic moment, it also enlarge the lattice constant, so the saturation decreases with the increasing substitution. With the increasing amount of Ti4+ ions, the coercivity of the films decreases. But coercivity of films increases as the increase of Sn⁴⁺ amount. The accessions of ZnFe₂O₄ bufferlayer can take up the strain at the buffer and substrate interface and they also can preclude interdiffusion at the surface between the substrates and the fims, thereby enhancing the performance of films.Through the research of sol-gel method to prepare NiZn ferrite thin films, the films we prepared had the performance of Ms with 386 emu/cm3 and Hc with 78Oe.