Structural, static and dynamic magnetic properties of dextran coated γ-Fe 2O 3 nanoparticles studied by 57Fe NMR, M?ssbauer, TEM and magnetization measurements
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Fardis, M.
Douvalis, A. P.
Tsitrouli, D.
Rabias, I.
Stamopoulos, D.
Kehagias, Th
Karakosta, E.
Diamantopoulos, G.
Bakas, T.
Papavassiliou, G.
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peer reviewed
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Journal of Physics Condensed Matter
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The structural and magnetic properties and spin dynamics of dextran coated and uncoated γ-Fe 2O 3 (maghemite) nanoparticles have been investigated using high resolution transmission electron microscopy (HRTEM), 57Fe nuclear magnetic resonance (NMR), M?ssbauer spectroscopy and dc magnetization measurements. The HRTEM observations indicated a well-crystallized system of ellipsoid-shaped nanoparticles, with an average size of 10nm. The combined M?ssbauer and magnetic study suggested the existence of significant interparticle interactions not only in the uncoated but also in the dextran coated nanoparticle assemblies. The zero-field NMR spectra of the nanoparticles at low temperatures are very similar to those of the bulk material, indicating the same hyperfine field values at saturation in accord with the performed M?ssbauer measurements. The T 2 NMR spinspin relaxation time of the nanoparticles has also been measured as a function of temperature and found to be two orders of magnitude shorter than that of the bulk material. It is shown that the thermal fluctuations in the longitudinal magnetization of the nanoparticles in the low temperature limit may account for the shortening and the temperature dependence of the T 2 relaxation time. Thus, the low temperature NMR results are in accord with the mechanism of collective magnetic excitations, due to the precession of the magnetization around the easy direction of the magnetization at an energy minimum, a mechanism originally proposed to interpret M?ssbauer experiments in magnetic nanoparticles. The effect of the surface spins on the NMR relaxation mechanisms is also discussed. © 2012 IOP Publishing Ltd.
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Average size, Bulk materials, Coated nanoparticles, DC magnetization, Energy minima, Hyperfine field, Inter-particle interaction, Longitudinal magnetization, Low temperature limit, Low temperature NMR, Low temperatures, Maghemites, Magnetic excitations, Magnetic nanoparticles, Magnetic studies, Magnetization measurements, Mossbauer, NMR relaxation, NMR spectrum, Orders of magnitude, Spin-spin relaxation time, Ssbauer spectroscopies, Static and dynamic, Structural and magnetic properties, Surface spins, Temperature dependence, Thermal fluctuations, Zero fields, Association reactions, Dextran, High resolution transmission electron microscopy, Iron ores, Magnetic properties, Materials handling equipment, Nanomagnetics, Nanoparticles, Nuclear magnetic resonance spectroscopy, Saturation magnetization, Temperature, Nuclear magnetic resonance, ferric ion, ferric oxide, nanoparticle, article, chemistry, magnetism, Mossbauer spectroscopy, transmission electron microscopy, X ray diffraction, Dextrans, Ferric Compounds, Magnetic Phenomena, Magnetic Resonance Spectroscopy, Microscopy, Electron, Transmission, Spectroscopy, Mossbauer, X-Ray Diffraction
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http://www.scopus.com/inward/record.url?eid=2-s2.0-84858743326&partnerID=40&md5=9e613b810385475180a2bb3a50e9d403
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Πανεπιστήμιο Ιωαννίνων. Σχολή Επιστημών και Τεχνολογιών. Τμήμα Βιολογικών Εφαρμογών και Τεχνολογιών