Dresden 2006 – wissenschaftliches Programm
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MA: Magnetismus
MA 32: Magnetic Particles / Clusters
MA 32.1: Vortrag
Donnerstag, 30. März 2006, 15:15–15:30, HSZ 401
The Mackay transition in Fe clusters — •Georg Rollmann, Alfred Hucht, Markus E. Gruner, and Peter Entel — Theoretical Low-Temperature Physics, University of Duisburg-Essen, Lotharstr. 1, Campus 47048 Duisburg, Germany
Icosahedral (Ih) structures are commonly observed in small clusters and even nanoparticles consisting of, e.g., rare-gas or transition-metal atoms. Their particular stability compared to corresponding cuboctahedral (CO), fcc-like packings is often related to their lower surface energy. However, due to the presence of internal strain, they become unfavorable for larger particles, and therefore a crossover from Ih to CO geometries is expected to occur with increasing particle size. Both packings can be transformed into one another via the Mackay transition [1].
We have investigated the potential energy surfaces of Fe clusters with closed atomic shells within density functional theory in the generalized gradient approximation allowing for full relaxation of the atoms. For Fe13, the CO geometry is not stable with respect to a Mackay transformation, resulting in an Ih ground state. However, in the case of Fe55, the lowest-energy isomer found is neither Ih nor CO, but has a CO-like core and an Ih shell. We also find these shell-wise transformed structures to be especially stable for larger Fe particles.
[1] A. Mackay, Acta Crystallogr. 15, 916 (1962)