||The dilute magnetic semiconductors is the semiconductor materials doped with transition elements, capable of room temperature ferromagnetism. However, the mechanism of oxide diluted magnetic semiconductor is not yet understood. In general, the mechanism for magnetic coupling, according to carrier concentrations can be explained by various mechanisms. When material is metal like, the magnetic coupling comes from RKKY interaction via high-density electrons. When the material is an insulator like, the magnetic coupling is mainly depended on, the defects that bound electrons to initiate magnetic coupling of those moments within the localized radius. For the material in semiconductor state, neither those two models nor other present models can explain their origins. Therefore we want to study Co doped ZnO with various oxygen vacancies (Vo) how Co and Vo affect the properties of the thin film and the room temperature ferromagnetism.|
The Zn0.95Co0.05O target was prepared by solid state reaction method at 860oC; and the thin films were grown by PF sputtering technique in reduced atmosphere of mixed hydrogen and argon with the different ratio. The effective oxygen vacancies is proved by X-ray photoelectron spectroscope (XPS), and is found to affect the crystal structure and the film surface observed by a X-ray Diffraction (XRD) and an Atomic Force Microscope (AFM), but the lattice c constant and crystalline size along c-axis don`t. Transmittance and Magnetic Circular Dichroism spectrometer (MCD) measurements, found that the magnetic band gaps of films are not changed with Vo. Both MCD and the superconductor quantum interference device (SQUID), confirm that all the thin films shows room temperature ferromagnetism which majorly come from ZnO band around 3.45eV, a few thin films exhibit other magnetism sources as well.