Microstructural, magnetic and optical characterizations of nanocrystalline Zn1-xMnxO dilute magnetic semiconductors synthesized by mechanical alloying

Nanocrystalline Mn doped Zn1-xMnxO (x = 0.02, 0.05, 0.07, 0.10) dilute magnetic semiconductors (DMSs) have been synthesized by mechanical alloying the stoichiometric mixtures of ZnO and MnO powders for different durations in a high energy planetary ball mill at room temperature under air medium. In the course of milling, the peak broadening of ZnO reflections increases continuously and MnO reflections disappear completely after 2 h of milling. Microstructure characterization of ball milled samples employing the Rietveld structure refinement using X-ray diffraction data reveals that the Zn2+ ions are replaced by Mn2+ ions and lattice parameters of ZnO matrix increase slowly due to this substitution. Particle size of these DMS decreases continuously with increasing Mn concentrations. XPS measurement indicates that the doped Mn ions possess both Mn2+ and Mn4+ valance states. Magnetic characterization of DMS samples shows room temperature ferromagnetism (RTF), which confirms the inclusion of Mn2+ in ZnO lattice and the RTF can be explained in the light of RKKY exchange interaction. Optical characterization of these DMS by UV-vis spectroscopy clearly reveals a red-shift and consequently the optical band-gap decreases with increasing Mn concentrations. (C) 2012 Elsevier B. V. All rights reserved.