| As one of high performance wide-band gap semiconductor material, ZnO has become the important materials for preparing the diluted magnetic semiconductors, due to its high Curie temperature and room temperature ferromagnetism. Because the ZnO based diluted magnetic semiconductor material doped by the transition metal has the characteristics of the electronic charge and spin at the same time, it has been widely applied in spintronic and optoelectronic fields. Hence, it is possible to fabricate the cache memory and create the permanent information storage using the electrical and magnetic properties, respectively. Therefore, it is expected to become the carrier of a new generation of information storage. In this thesis, pure and Fe doped ZnO films have been prepared by the magnetron sputtering, and the effect of the doping amount of Fe, annealing temperature and atmosphere on the Ferromagnetism at room temperature and microstructure of samples have been studied. We have also explained the source of room-temperature ferromagnetism with the consideration of the defects of microstructure in the Fe doped ZnO nano-films.1. Pure ZnO and Zn1-xFexO(x = 1.0%, 3.0%, 5.0% and 7.0%) films were deposited on Si substrate by magnetron sputtering, and the Fe doped ZnO dilute magnetic semiconductor nano-film has been obtained after annealing treatment with different temperature in vacuum and air, respectively. The microstructure, surface morphology, element composition, element chemical valence state and Ferromagnetism of the samples were characterized by using X-ray diffraction(XRD), scanning electron microscope(SEM), energy spectrometer(EDS), X-ray photoelectron spectrometer(XPS) and vibrating sample magnetometer(VSM).2. XRD analysis has shown that the structure of all the samples is hexagonal wurtzite, with preferential growth along the c axis. Fe doping and the annealing temperature have an influence on the microstructure of films. With the increasing of Fe doping amount, the intensity of diffraction peaks increase first and then decrease gradually, and the stress in films increase and the grain size decrease gradually. When the annealing temperature was as high as 450 oC, a strongest diffraction peak(002) appeared, and a biggest grain size was observed, and the crystallinity and orientation of the films obviously became better. The size of film grain became smaller and the diffraction peak intensity obviously decrease as the annealing temperature rising. The SEM images of the sample surface and cross sections show that Fe doping have improved the uniformity and the surface density of the grain size of ZnO:Fe nano-film. With the increase of annealing temperature, the flatness of film surface is improved gradually and the grain size becomes larger and nonuniform. In addition, the thickness of films decrease with the increase of doping concentration, and an largest average thickness was obtained when the film had been annealed at 450℃ in air. According to the EDS spectrum, the Fe ions have been successfully doped into ZnO films, and through the XPS analysis, it can be seen that Fe exists in the thin film by Fe2 + and Fe3 + valence state.3. The ferromagnetism measurement was carried out using VSM, and the results show that all the samples have a perfect S-shaped hysteresis loop, which has the obviously ferromagnetism at room temperature. It also can be found that the doping amount of Fe element, annealing temperature and atmosphere have the influence on the ferromagnetism. With the increase of the Fe element doping amount, the saturation magnetization intensity decreases gradually, but still more than that of pure ZnO. As the annealing temperature rising, the magnetic intensity increase gradually. The magnetization intensity of the thin films annealing in the air are all less than that of the pure ZnO thin films. Finally, we have explained the Ferromagnetism with the theory of defects and the surrounding magnetic ions to form bound magnetopolaron(BMP). |
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