Eur. Phys. J. D 43, 27-32 (2007)
https://doi.org/10.1140/epjd/e2007-00066-0

Model predictions and experimental characterization of Co-Pt alloy clusters

¹ Physique des Solides Irradiés et des Nanostructures, CP 234, Université Libre de Bruxelles, Bd du Triomphe, 1050 Bruxelles, Belgium
² Laboratoire de Physique de la Matière Condensée et Nanostructures, Université Lyon 1, CNRS UMR 5586, Domaine Scientifique de la Doua, 69622 Villeurbanne Cedex, France

Corresponding author: ^a mhou@ulb.ac.be

Received: 24 July 2006
Revised: 3 October 2006
Published online: 24 May 2007

Abstract

Model and real cobalt-platinum alloy clusters are compared in terms of structure, composition and segregation. Canonical and semi grand canonical Metropolis Monte Carlo simulations are performed to model these clusters, using embedded atom (EAM) and modified embedded atom (MEAM) potentials. All of them correctly predict the bulk L1₂ Co₃Pt and CoPt₃ structures as well as the L1₀ CoPt phase. However, the lattice parameters, phase stability and the L1₀-fcc order-disorder transition temperature are at variance. Segregation predictions with EAM and MEAM potentials are contradictory. Experimentally, mixed clusters with various compositions were deposited by Low Energy Cluster Beam on amorphous carbon at room temperature. Their size distribution, crystalline structure and composition were examined by Transmission Electron Microscopy (TEM). Clusters with the same size distributions were modelled. Both experiment and modelling show their crystallographic parameters to continuously correspond to the fcc CoPt chemically disordered phase. Diffraction measurements indicate surface segregation of the specie in excess, in agreement with EAM predictions for the Co-rich phase. The consequences on magnetic properties are discussed.