Browsing by Author "Kassabova-Zhetcheva V.D."

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    Characterization of superparamagnetic MgxZn1-x Fe2O4 powders
    (2007-03-01) Kassabova-Zhetcheva V.D.; Pavlova L.P.; Samuneva B.I.; Cherkezova-Zheleva Z.P.; Mitov I.G.; Mikhov M.T.
    Structural and magnetic properties of MgxZn1-x Fe2O4 powders have been studied with respect to the application for thermal cancer therapy (magnetic hyperthermia). MgxZn1-xFe2O4 (x = 0.1-0.5) powders with particle sizes between 5 and 8 nm were produced by citrate method. The X-ray diffraction patterns of the samples correspond to a spinel phase. The lattice constant and the volume of the elementary cell increase when x changes from 0.1 to 0.5. The FTIR-spectra ascertain the spinel phase formation. The Mossbauer studies reveal the presence of extremely small particles, which undergo superparamagnetic relaxation at room temperature. The core-shell model has been applied to explain quadruple doublets. The quadruple splitting at ``shells`` is bigger than those at ``cores`` whereas the isomer shifts remain close. Magnetic studies confirm the presence of extremely small particles that behave as superparamagnetic ones. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2006.
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    Characterization of the citrate precursor, used for synthesis of nanosized Mg-Zn ferrites
    (2009-07-10) Kassabova-Zhetcheva V.D.
    The citrate precursor has been used to synthesize nanocrystalline Mg-Zn-ferrites. The nature of the prepared precursor is characterized and compared with those of the precursors studied earlier, prepared by the same process. The study has been performed by inorganic and organic elemental analyses, Fourier Transformed Infrared Spectroscopy (FTIR), Mössbauer spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Electron Paramagnetic Resonance (EPR), Electronic absorption spectrometry in the UV-VIS region, Differential Thermal analysis/ Thermogravimetry (DTA-TG) analyses, and X-ray diffraction (XRD) analysis. The collected results determined the precursor as a coordination polymer with monomer unit (NH4)4{M [Fe(C6H5O7)2]2}, where M = Zn or Mg. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.