Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 12: Nanostructures at surfaces: Dots, particles, clusters I (magnetic)

O 12.4: Talk

Monday, March 23, 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 T_B of the clusters is below the Curie temperature of the substrate T_C. For ferromagnetic clusters, materials with higher anisotropy are required.

[1] M. Schmid et. al., Phys. Rev. Lett. 99, 196104 (2007).