Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 8: Magnetic Particles / Clusters I

MA 8.6: Vortrag

Montag, 26. März 2012, 19:00–19:15, EB 202

Correlation of superparamagnetic relaxation with magnetic dipole and exchange interaction in capped iron-oxide nanoparticles — •Joachim Landers, Frank Stromberg, Masih Darbandi, Werner Keune, and Heiko Wende — Faculty of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen

Iron-oxide nanoparticles with a mean diameter of 6 nm capped with organic surfactants and/or silica shells of various thicknesses have been prepared by a microemulsion method. The resulting different particle distances imply a tunable contribution of magnetic dipole interaction to the effective magnetic anisotropy. Bare particles of the same size were used as a reference. To determine superparamagnetic relaxation parameters temperature dependent Mössbauer spectra were measured in the range of 4.2 - 300 K. Calculations using a many state relaxation model of magnetic orientations were done to estimate effective anisotropies which are influenced by surface and interaction contributions. A decrease of the blocking temperature with progressive coating thicknesses was observed by several FC-ZFC magnetization measurements in good agreement with Mössbauer results. Calculated values of the relaxation frequency were compared with AC susceptibility and thermoremanent relaxation measurement (TRM) data in attempt to obtain information about surface and volume contributions to the distribution of anisotropy energies. Supported by DFG (WE 2623/3-1)