Berlin 2012 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 12: FePt Nanoparticles (jointly with MA, MM – Organizer: Farle)

DS 12.3: Topical Talk

Montag, 26. März 2012, 16:00–16:30, EB 202

Pt surface segregation and its impact on magnetism in FePt nanoparticles — •Ulf Wiedwald — Institut für Festkörperphysik, Universität Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany

The appealing magnetic properties of chemically ordered FePt alloys strongly depend on composition. In nanoparticles with diameters below 10 nm the relative number of surface-near atoms strongly increases, thus any tendency of segregation will significantly change the stoichiometry of the interior. As a result, magnetic moments as well as magnetic anisotropy may vary compared to the bulk. In the frame of the collaborative research center SFB 569 we prepared size-selected, hexagonally arranged metallic particles by precursor loaded reverse micelles and plasma etching [1]. Pt segregation [2] and its impact on magnetism were examined in-situ for naked, non-interacting FePt particles on Si/SiO₂ as function of size (2-10nm) by photoelectron spectroscopy and x-ray magnetic circular dichroism. For partially L1₀-ordered particles we observe reduced spin moments with decreasing diameter while the orbital moment is found rather independent of size. As connected to the orbital magnetism, the effective magnetic anisotropy is also conserved for decreasing diameters, though reduced relative to the bulk [3]. Reasons for these astonishing observations are discussed.
A. Ethirajan, U. Wiedwald, et al., Adv. Mater. 19, 406 (2007).
L. Han, U. Wiedwald, B. Kuerbanjiang, P. Ziemann, Nanotechnology 20, 285706 (2009).
U. Wiedwald, L. Han, J. Biskupek, U. Kaiser, P. Ziemann, Beilstein J. Nanotechnol. 1, 24 (2010).