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ICAME 2005

Proceedings of the 28th International Conference on the Applications of the Mössbauer Effect (ICAME 2005) held in Montpellier, France, 4-9 September 2005, Volume I

ICAME 2005 by P.-E. Lippens
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Nano-sizedmaterialsarecurrentlyofgreattechnologicalimportanceandconsequently,one of the research subjects under intense investigation for their mechanical, electrical or chemicalpropertiesduetothefactthatthepropertiesofthenanophasesbeingverydifferent from those of the bulk material. Nanoparticles of materials are likely to improve dramaticallythepropertiesoftheresultingmaterial.Consequently,thesynthesisofspinel ferrite nanoparticles has been intensively studied in recent years due to their potential applicationinhigh-densitymagneticrecording,microwavedevicesandmagneticfluids. 2Experimental Cobalt ferrite powders (CoFe O, x=1 or 2) were prepared from co-precipitation of x 3?x 4 layered iron–cobalt hydroxide carbonates x-LDH–CO, by high-energy ball-milling or 3 annealing thermal treatment. The starting materials used were Fe(NO)·9HO (purity 3 3 2 99%),Co(NO)·6HO(purity96%)andNaCO. 3 2 2 2 3 The powder X-ray diffraction (XRD) patterns were recorded by use of a TUR M62 diffractometer with Co-K? radiation (?=1.789 Å). The observed patterns were cro- matched with those in the JCPDS database. Transmission Electron Microscopy (TEM) investigationsweremadeusingaTopcon002Belectronmicroscopeoperatingat200kV with a point-to-point resolution r=1.8 Å. The samples were sonicated in ethanol and deposited onapre-depositedpolymer onacoppergrid.Mössbauerspectraofnano-size cobalt ferrite particles were recorded at 295 and 77 K on a Wissel electromechanical Mössbauer spectrometer (Wissenschaftliche Elektronik GmbH, Germany) working in a 57 constant acceleration mode. A Co/Cr (activity?10 mCi) source and an?-Fe standard were used. The experimental spectra were treated using the least squares method. The parametersofhyperfineinteractionsuchasisomershift(IS),quadrupolesplitting(QS)and effectiveinternalmagneticfield(H )aswellasthelinewidths(FWHM)andtherelative eff weight(G)ofthepartialcomponentsofthespectraweredetermined.Temperatureandfield dependencesofthemagnetizationofthecobaltferriteweremeasuredonaQuantumDesign MPMS-XLSQUIDoperatinginthetemperaturerange2–400Kandanappliedfieldupto 5T.Inordertoavoidsamplerotationintheappliedfieldthenanoparticleswereembedded inapolymermatrix,PMMA(polymethylmethacrylate). 3Resultsanddiscussion NearlysphericalCoFeO nanoparticleswereobtainedbyhighenergyballmillingofthe 2 4 1-LDH-CO.X-raypowderdiffractionandTransmissionElectronMicroscopyshowthat 3 theaveragesizeoftheparticlesincreases(ca.5,8and20nm)withmillingtime(ca.5,10 and15h).Theincreaseinsizeisalsoevidencedbythereductionofthemicrostrainthatis commonlyassociatedwithadiminutionofstructuraldefects.Itisinterestingtonotethatthe processofcrystallizationcontinuesasafunctionoftreatmenttimeandatlaterstagesis accompanied by the reduction to cobalt. Similarly, Menzel et al. have shownthat hi- energymillingofnickelferritespinelsinducestheformationofmetalliciron[1].
Springer Berlin Heidelberg; December 2007
725 pages; ISBN 9783540498506
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Title: ICAME 2005
Author: P.-E. Lippens; J.-C. Jumas; J.-M. Génin
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