Structural, Optic, and Magnetic Investigation of the Synthesized ZnO and Zn$_{0.99}$Co$_{0.01}$O Semiconductors via Solid State Reaction

Abstract

Both ZnO and Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.99</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.01</sub> O 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 Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.99</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.01</sub> O, and 1.3 ± 0.2% for ZnO. Substitutions of Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> ions with Zn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> 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 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> * levels. The ferromagnetic effect of Co doping in ZnO lattice was revealed by the coercivity of ~154±50 Oe and positive Curie-Weiss temperature, 79 ± 1 K. Beside ferromagnetic interactions, the calculated effective Bohr Magnetron (¿ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ), 0.32±0.01 ¿ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> , suggested anti-ferromagnetic interactions due to be less than the theoretical spin based magnetic moment of Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions, 3.0 ¿ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> .