Structural, Optic, and Magnetic Investigation of the Synthesized ZnO and Zn0.99Co0.01O Semiconductors via Solid State Reaction

Abstract

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 +/-0.1%, and also showed a contamination of tungsten (W) atoms, in the atomic ratio of 1.6 +/- 0.2% for Zn0.99Co0.01O, and 1.3 +/- 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 +/- 0.01 eV to 3.03 +/- 0.01 eV, and the existence of newly permitted transitions between intra ionic levels. The ferromagnetic effect of Co doping in ZnO lattice was revealed by the coercivity of similar to 154 +/- 50 Oe and positive Curie-Weiss temperature, 79 +/- 1 K. Beside ferromagnetic interactions, the calculated effective Bohr Magnetron (mu(eff)), 0.32 +/- 0.01 mu B, suggested anti-ferromagnetic interactions due to be less than the theoretical spin based magnetic moment of Co2+ ions, 3.0 mu B.