Preparation And Electromagnetic Properties Control Of NiZn Ferrite Films

The rapid development of modern electronic information technology have put forward higher requirements to microwave magnetic materials—high resonance frequency, high magnetic permeability and high resistivity. Soft magnetic ferrite materials have the advantages of high resistivity and low eddy current loss, however, its low resonant frequency (< 200 MHz) limits the applications in devices such as high-frequency inductors. Therefore, people are focused on how to improve the resonance frequency and magnetic permeability of soft magnetic ferrites. In this thesis, NiZn ferrite powders were synthesized by the co-precipitation method. The ferrite powders were compressed into target and sintered under high temperature, NiZn ferrite films were deposited by using radio frequency magnetron sputtering. Crystal structure, static magnetism and high frequency magnetic properties of the samples were characterized by X-ray diffraction spectrum, hysteresis loop and ferromagnetic resonance absorption spectrum. The main results were as follows:1. Through the co-precipitation method nickel ferrite nanoparticles were prepared, by compositing with ZnO nano particles an enhancement of high frequency performance was achieved. By controlling the mixing ratio, we found that when the mixing ratio of Ni ferrite was 70% the high frequency performance was optimized. The result shows that by preparing ferrite materials into nano-structure the high frequency performance can be improved.2. Based on the conclusion that the high frequency performance can be improved in nano-structured ferrite materials, Ni ferrite films were deposited by magnetron sputtering. By controlling the magnetron sputtering parameters such as the sputtering distance and gas pressure, we found Ni ferrite film with good spinel phase can be deposited under room temperature without high temperature sintering. The method of preparing well crystallized ferrite film under room temperature was proposed, which is of great importance to industrialization of ferrite devices.3. Using the room temperature preparation method, Ni ferrite films with different thicknesses were fabricated. It was found that at the initial growth stage ferrite crystal was irregular, and the grain size was small, which was caused by the big mismatch between the substrate and ferrite crystal. As a result the thinnest film (10 nm) was superparamagnetic. The research is helpful to improve the static magnetic properties of ultra-thin ferrite films.4. Based on the bianisotropy model, the resonance frequency can be controlled by anisotropy field. NiZn ferrite film with magnetic anisotropy was prepared on PMN-PT substrate. The change in direction and magnitude of the anisotropy by electric field application was observed in the NZFO/PMNPT heterostructure by applying electric fields across the sample. We found that high frequency properties of ferrite thin films can be improved through magnetoelectric coupling effect.5. The NiZn ferrite film have high resistivity, by investigating the resistivity of films prepared under different conditions, resistive switching effect was observed. The influence of external magnetic field, annealing temperature and forming current on the resistive switching behavior of NiZn ferrite film was studied. We found that by controlling the annealing temperature and forming current both conductive filaments induced and interface induced resistive switching effects can be achieved. The research is important to the development of device that can hold electric and magnetic information at the same time.