Finite size effects on structure and magnetism in mass-selected CoPt nanoparticles*
LPMCN, UMR 5586 CNRS/Université de Lyon,
2 ITP, Institut für Theoretische Physik, Universität Kassel, 34132 Kassel, Germany
3 European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France
Received in final form: 8 November 2012
Published online: 26 February 2013
We have studied size effect on the local structure and magnetism in CoPt clusters embedded in carbon matrix upon annealing in the 2–4 nm diameter range. From Co-K and Pt-L edges extended X-ray absorption fine structure (EXAFS) experiments and simulations, we report the refined quantitative non trivial structure of size-selected 3 nm in diameter CoPt magnetic clusters. In agreement with ab-initio simulation calculations, we evidenced an element-specific dependence of the local atomic relaxations in CoPt clusters leading to a strong distortion in pure Co planes. Since pure Co layers do not match the underlying Pt layer in chemically ordered L10-like clusters, we claim that a perfect crystal can not exist at nanosize. Such result could explain the low magnetic anisotropy energy measured on chemically ordered CoPt nanomagnets assemblies.
ISSPIC 16 – 16th International Symposium on Small Particles and Inorganic Clusters, edited by Kristiaan Temst, Margriet J. Van Bael, Ewald Janssens, H.-G. Boyen and Françoise Remacle.
Present address: Institut Lumière Matière, UMR 5306 Université Lyon 1-CNRS, Université de Lyon, 69622 Villeurbanne Cedex, France.
Present address: Currently at Institut NÉEL, CNRS and Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France.
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag 2013