Eur. Phys. J. B (2013) 86: 83
https://doi.org/10.1140/epjb/e2013-30644-0

Regular Article

Specific local relaxation and magnetism in mass-selected CoPt nanoparticles^*

¹ LPMCN, UMR 5586 CNRS/Université de Lyon, 69622 Villeurbanne Cedex, France
² Institut NÉEL, CNRS & Université Joseph Fourier, BP166, 38042 Grenoble Cedex 9, France
³ LCBMN, Facultad de Ciencias, Universidad Autónoma del Estado de México, 50000 Toluca, Mexico
⁴ ITP, Institut für Theoretische Physik, Universität Kassel, 34132 Kassel, Germany

^a e-mail: veronique.dupuis@univ-lyon1.fr

Received: 19 July 2012
Received in final form: 21 December 2012
Published online: 6 March 2013

Abstract

We report the refined quantitative magnetic moments of size-selected 3 nm in diameter CoPt clusters at both Co and Pt-L_{2,  3} edges. By combining the high photon flux and the chemical selectivity of the synchrotron radiation delivered on ESRF beam lines, we have studied size effect on the local structure and magnetism in CoPt clusters embedded in carbon matrix upon annealing. On one hand, from Pt-L edges extended X-ray absorption fine structure (EXAFS) experiments and simulations associated to previous Co-K edge ones, we have determined the first-shell Co-Co, Co-Pt and Pt-Pt coordination numbers and mean atomic distances in agreement with recent VASP ab initio calculations obtained for L1₀-like clusters. On the other hand, X-ray magnetic circular dichroism (XMCD) investigations have revealed a significant increase of both Co and Pt magnetic moments for the chemically ordered CoPt clusters compared to the bulk values while the magnetic anisotropy energy (MAE) of annealed samples is twice that of the as-prepared samples, but one order of magnitude smaller than what is expected for the L1₀ CoPt bulk.