Thesis & Dissertations

This thesis represents a study of structural, optical and magnetic properties of undoped ZnO, Mn doped ZnO (Zn1-xMnxO) and Mn2O3 nanoparticles at room temperature. The samples were prepared via Co-Precipitation technique using ZnCl2, NaOH and MnCl2 solutions with 0.00≤x≤0.10at.%. The manganese doping had an enormous effect on different properties of undoped ZnO nanoparticles. XRD spectra showed that Zn1-xMnxO nanoparticles have hexagonal wurtzite structure with the preferred orientation of (101) planes, while Mn2O3 nanoparticles have cubic structure. For x≥0.05, some peaks were observed for ZnMnO3 impurity pointing that the solubility of Mn2+ in ZnO is up to 5at.% . The lattice parameters (a and c) ofZn1-xM and a for Mn2O3 were calculated from the XRD spectra and were consistent with the standard values. For the doped ZnO nanoparticles, the lattice parameters increased with x. Using TEM technique, the micrographs of all the samples were obtained with different sizes and shapes, where they are spherical and nanorod nanoparticles for Zn1-xMnxO aof laciaehas ofa ,Mn2O3 nanoparticles. The crystallite sizes calculated from XRD spectra, using Debye-Sherrer’s method and Williamson-Hall methods, showed a similar trend to the TEM technique with a range of 9-63nm and 17.3nm for Zn1-xMnxO and Mn2O3, respectively. The results of Zn and Mn contents were carried out using PIXE and RBS techniques and were very close to the nominal stoichiometric ratios, whereas RBS technique revealed an oxygen vacancy in all samples. In UV analysis, the absorption peak of the Mn doped ZnO samples showed a blue shift towards smaller wavelengths. The energy band gap (Eg) decreased from 3.09 eV (x=0.00) to 2.56eV(x=0.10) with the increase in Mn content. For Mn2O3, Eg is found to be 1.24eV. The functional groups of the samples were detected using FTIR spectra where two major peaks were observed for all samples. The M-H loops were performed at room temperature and the undoped ZnO showed an intrinsic ferromagnetism and it may be restricted to the oxygen vacancy confirmed by RBS stoichiometry. The ferromagnetic nature decreased for the doped samples except for x=0.03 that was probably due to the direct exchange interaction that led to antiferromagnetic coupling between neighboring Mn2+ ions. Paramagnetic signals were observed for x≥0.05 which was due to small secondary phases which is ZnMnO3. For x=0.01 and 0.10, the M-H loops are very narrow. This was due to the small crystallite sizes with single domains below a critical value, where the nanoparticles tend to be superparamagnetic. The M-H loop of the Mn2O3 sample showed the antiferromagnetic behavior with a paramagnetic signal. The EPR spectra confirmed the strong ferromagnetic nature of the undoped ZnO nanoparticles and the Mn doped ZnO nanoparticles with x=0.03. The width of the ferromagnetic signal decreased for the other samples which verified the results obtained from M-H loops. The g-factor was calculated for Zn1-xMnxO samples and it decreased upon doping within the range of 2.17-2.01. The EPR spectrum for Mn2O3 was with high intensity due to the existence of Mn2+ ions on the surface and the g-factor was found to be 1.985.