Berlin 2005 – wissenschaftliches Programm
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MA: Magnetismus
MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65
MA 20.83: Poster
Montag, 7. März 2005, 14:00–18:00, Poster TU C
Interface Magnetism in Co/CoO core-shell nanoparticles — •U. Wiedwald1, H.-G. Boyen1, J. Eisenmenger1, F. Weigl1, K. Zürn1, P. Ziemann1, K. Fauth2, J. Lindner3, M. Spasova3 und M. Farle3 — 1Abteilung Festkörperphysik, Universität Ulm, D-89069 Ulm — 2Experimentelle Physik IV, Universität Würzburg, Am Hubland, D-97074 Würzburg — 3Institut für Physik, Universität Duisburg-Essen, D-47048 Duisburg
Colloidal Co particles (9-13 nm) were prepared by organometallic synthesis. The magnetism of these particles is heavily influenced by unavoidable surface modifications due to the attachment of hydro-carbonic ligands and the formation of a 2-3 nm thick antiferromagnetic CoO layer. To study the magnetic response of both Co/CoO core-shell particles and ligand-free metallic particles we employed a combination of hydrogen and oxygen plasma treatments. The degree of surface oxidation/reduction was tracked by x-ray absorption spectroscopy. By combining para/ferro-magnetic resonance techniques with x-ray magnetic circular dichroism we quantitatively address the interface magnetism of the particles. Core-shell Co/CoO particles show a rigorous increase in the ratio of orbital-to-spin magnetic moment while metallic Co particles reveal the expected fcc bulk-like behaviour for particles with a low ratio of surface-to-volume atoms (d > 8 nm). The separation of the magnetic dichroism of Co atoms in metallic and oxidic environments suggests that the exchange coupling at the interface favours parallel alignment. All results are compared with detailed structural analysis by high-resolution transmission electron microscopy.