Journal
JOURNAL OF ALLOYS AND COMPOUNDS
Volume 655, Issue -, Pages 244-252Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jallcom.2015.09.166
Keywords
ZnO; Cobalt doped ZnO; Magnetic properties; Optical properties; Red shift; sp-d exchange interaction
Categories
Funding
- Kuwait University [GS 02/10, GS 02/08]
- Semiconductor research facility, research administration [GE01/08]
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We carried out a systematic study on the effect of Co doping on the structural, magnetic and optical properties of ZnO nanocrystalline particles, using x-ray diffraction, x-ray photoelectron spectroscopy (XPS), Quantum Design PPM5-9 magnetometry, and Ultra Violet-Visible spectroscopy. The Zn1-xCoxO nanoparticles with 0 <= x <= 0.1 were successfully prepared by the formal solid-state reaction method. The XPS results and the XRD analysis with full structural Rietveld refinement reveals that all Zn1-xCoxO nanocrystalline particles in this Co-doping range have hexagonal wurtzite structure. Co atoms have been successfully incorporated in tetrahedral sites and no secondary phases or Co rich clusters were detected. For all Co-doped ZnO nanoparticles under investigation, the field dependence of the magnetization curves exhibits ferromagnetic behavior with relatively small coercive fields at room temperature. The coercive fields increased with Co-doping and decreased with temperature, as expected. In addition, we found a signature for antiferromagnetic ordering between the Co ions. We also observed a strong correlation between the magnetic and optical behavior of the Co-doped ZnO nanoparticles. Optical diffuse reflectance and absorption spectra exhibit a red shift at room temperature in the absorption band edge with increasing Co-doping. The red shift is attributed to the sp-d exchange interaction between free charge carriers in ZnO band and the localized magnetic moments. (C) 2015 Elsevier B.V. All rights reserved.
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