Preparation And Magnetic Properties Of Zn_0.98Co_0.02O/PbZr_0.52Ti_0.48O₃ Heterostructures

In this thesis, Zn_0.98Co_0.02O diluted magnetic semiconductor thin films were prepared by pulsed laser deposition (PLD), and their ferromagnetism origins were investigated. Then, Zn_0.98Co_0.02O/PbZr_0.52Ti_0.48O₃ heterostructures were fabricated by PLD, and their ferromagnetism modulations under electric-field were discussed. The main research contents and the obtained results are summarized as follows:1. Preparation and ferromagnetism of Zn_0.98Co_0.02O thin filmsZn_0.98Co_0.02O thin films were prepared on Si (100) substrates under 450, 550 and 650 oC by PLD. The chemical compositions, magnetic properties and fine structures of the prepared films were characterized by X-ray diffraction (XRD), magnetic force microscopy (MFM), superconducting quantum interference device (SQUID), and extended X-ray absorption fine structure (EXAFS). The origin of ferromagnetism in Zn_0.98Co_0.02O thin films was also discussed. The MFM results show that there is no magnetic purity in the prepared films. The M-H curves indicate all prepared thin films exhibit room temperature ferromagnetism, and the saturated magnetization decreases with the increment of the substrate temperature. The EXAFS studies show that Co ions exist as substitutional Co2+ in the Zn_0.98Co_0.02O thin films when the substrate temperature is lower than 650 oC and then evolve into a secondary phase of Co3O4 when the substrate temperature is higher than 650 oC. In addition, the intrinsic ferromagnetism of Zn_0.98Co_0.02O thin films is explained by bound magnetic polarons (BMPs) model.2. Ferromagnetism of Zn_0.98Co_0.02O films prepared on Zn0.97Al0.03O buffer layerZn_0.98Co_0.02O films were prepared on Zn0.97Al0.03O buffer layer under 450, 550, and 650 oC by PLD. The resistance of Zn0.97Al0.03O buffer layer was characterized to be about 155 ? from I-V curves by scanning probe microscopy. MFM measurements show there is no obvious magnetic impurities. SQUID results indicate that the ferromagnetism of Zn_0.98Co_0.02O films can be enhanced by the Zn0.97Al0.03O buffer layer, which is explained by BMPs model.3. Preparation and ferromagnetism modulation of Zn_0.98Co_0.02O/PbZr_0.52Ti_0.48O₃ heterostructuresZn_0.98Co_0.02O/PbZr_0.52Ti_0.48O₃ heterostructures were prepared by PLD on Zn0.97Al0.03O buffer layer at oxygen atmospheres with 20, 50, and 200 mTorr. XRD results demonstrate the crystallinity of the heterostructure improves with the increment of oxygen pressure. The stripe-like magnetic domains are observed at room temperature in Zn_0.98Co_0.02O/PbZr_0.52Ti_0.48O₃ heterostructures, which indicates the room temperature ferromagnetism. Excellent piezoelectric properties are shown in heterostructures by piezoresponse force microscopy (PFM). The obvious ferromagnetism modulations under electric field are found, and the corresponding mechanism is also discussed.