Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 12: Nanostructures at surfaces: Dots, particles, clusters I (magnetic)
O 12.4: Vortrag
Montag, 23. März 2009, 15:45–16:00, SCH A215
Structural and Magnetic Properties of Fe and Co Clusters on Alumina/Ni3Al(111) — •Andreas Buchsbaum1, Maurizio De Santis3, Helio Tolentino3, Georg Kresse2, Michael Schmid1, and Peter Varga1 — 1Inst. f. Allg. Physik, TU Wien, Austria — 2Faculty of Physics, CMS, University of Vienna, Austria — 3Institute Neel, CNRS Grenoble, France
The structure of the ≈ 5 Å thick aluminum oxide on Ni3Al(111), which has been solved recently, exhibits holes at the corner of the (√67 × √67)R12.2 ∘ unit cell, reaching down to the metal substrate [1]. Therefore, the ultrathin oxide film, forming a nanomesh with a 4.1 nm lattice, is a perfect template for growing highly regular arranged metal clusters. Pd atoms trapped in the corner holes, create metallic nucleation sites, where Fe as well as Co clusters can nucleate and form a well-ordered hexagonal arrangement on the oxide nanomesh [1]. We have studied the morphology of the Fe and Co clusters and applied different methods to determine the orientation of the clusters. For Fe we found cluster growth in either bcc[110] or bcc[100] direction, depending on the deposition temperature and for Co we found close-packed planes on top of the clusters and random stacking of fcc and hcp planes. As the cluster size is limited to < 4 nm, pure Fe and Co clusters are superparamagnetic at temperatures where the Ni3Al substrate is paramagnetic, i.e., the blocking temperature TB of the clusters is below the Curie temperature of the substrate TC. For ferromagnetic clusters, materials with higher anisotropy are required.
[1] M. Schmid et. al., Phys. Rev. Lett. 99, 196104 (2007).