Zhang, Z. John

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    Magnetic properties of bulk Zn₁₋ₓMnₓO and Zn₁₋ₓCoₓO single crystals
    (Georgia Institute of Technology, 2004-12) Kane, Matthew Hartmann ; Shalini, K. ; Summers, C. J. ; Varatharajan, R. ; Nause, J. ; Vestal, Christy Riann ; Zhang, Z. John ; Ferguson, Ian T. ; Georgia Institute of Technology. Center for Organic Photonics and Electronics ; Georgia Institute of Technology. School of Electrical and Computer Engineering ; Georgia Institute of Technology. School of Materials Science and Engineering ; Cermet, Inc. ; Georgia Institute of Technology. School of Chemistry and Biochemistry
    Manganese and cobalt-doped ZnO have been produced using a modified melt-growth technique. X-ray diffraction measurements indicate that the samples are high-quality single crystals with ω−2θ full width at half maximum values of 78 arc sec for the undoped ZnO and 252 arc sec for Zn₁₋ₓMnₓO (x = 0.05). The lattice parameter of the Zn₁₋ₓMnₓO was observed to increase with Mn concentration. Transmission measurements showed systematic variations dominated by absorption from interatomic Mn²⁺ and Co²⁺ transitions. No evidence of diluted magnetic semiconductor mean-field ferromagnetic behavior was observed in any of these nominally noncarrier-doped samples. The magnetic properties instead showed paramagnetic behavior for Zn₁₋ₓMnₓO dominated by an antiferromagnetic Mn–Mn exchange interaction at low temperatures. Zn ₁₋ₓ CoₓO showed hysteresis that was attributed to superparamagnetic Co clusters embedded in a diamagnetic ZnO matrix. It has been shown that in the bulk single-crystal form, intrinsic and noncarrier-doped Zn₁₋ₓTMₓO is not ferromagnetic; thus creative processing and doping techniques are necessary to achieve practical ferromagnetism in these materials.