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Both ZnO and Zn0.99Co0.01O semiconductors were synthesized through solid state reaction via mechanical milling and thermal treatment. Initially the wurtzite ZnO structures of the synthesized particles were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Since these techniques were unable to identify both contamination atoms and Co distribution, energy dispersive X-ray spectrometry (EDS) was used. EDS showed a successful doping of Co atoms with the atomic ratio of 0.9 Â± 0.1%, and also showed a contamination of tungsten (W) atoms, in the atomic ratio of 1.6 Â± 0.2% for Zn0.99Co0.01O, and 1.3 Â± 0.2% for ZnO. Substitutions of Co+2 ions with Zn+2 host atoms in the ZnO lattice were exposed through X-ray photo spectroscopy (XPS) data of Co 2p electronic energy levels. UV-vis absorption spectroscopy (UV-vis) was also used to prove Co substitutions in the ZnO lattice. This was revealed by a decrease in band gap from 3.25 Â± 0.01 eV to 3.03 Â± 0.01 eV, and the existence of newly permitted transitions between intra ionic d-d* levels. The ferromagnetic effect of Co doping in ZnO lattice was revealed by the coercivity of ~154Â±50 Oe and positive Curie-Weiss temperature, 79 Â± 1 K. Beside ferromagnetic interactions, the calculated effective Bohr Magnetron (Â¿eff), 0.32Â±0.01 Â¿B, suggested anti-ferromagnetic interactions due to be less than the theoretical spin based magnetic moment of Co2+ ions, 3.0 Â¿B.
Date of Publication: June 2010