Zhang, Z. John

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    Faraday rotation in Co₀.₈₅Zn₀.₁₅Fe₂O₄ spinel ferrite nanoparticulate films under low applied fields
    (Georgia Institute of Technology, 2004-04) Anderson, Richard M. ; Vestal, Christy Riann ; Samia, Anna C. S. ; Zhang, Z. John ; Center for Organic Photonics and Electronics ; Georgia Institute of Technology. School of Chemistry and Biochemistry
    Films of Co₀.₈₅Zn₀.₁₅Fe₂O₄ nanoparticles were prepared on silanized glass substrates using aminobenzoic acid/imidazole-modified magnetic nanoparticles. Dispersive Faraday rotations in the nanoparticulate films were observed as 1.0°–3.0° under relatively low applied magnetic field strengths of less than 500 Oe. The magnitude of the Faraday rotation increases with increasing thickness of the prepared films. No differences in the Faraday rotation were observed for Co0.85Zn0.15Fe2O4 nanoparticles as the particle size varied from 12 to 18 nm.
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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. ; 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.