Specific local relaxation and magnetism in mass-selected CoPt nanoparticles

• Published in: The European physical journal. B, Condensed matter physics Vol. 86; no. 3
• Main Authors: Dupuis, Veronique, Blanc, Nils, Díaz-Sánchez, Luis Enrique, Hillion, Arnaud, Tamion, Alexandre, Tournus, Florent, Pastor, Gustavo Miguel
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.03.2013; EDP Sciences; Springer
• Subjects: Anisotropy; Chemical Sciences; Cobalt; Complex Systems; Condensed Matter Physics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Engineering Sciences; Exact sciences and technology; Fluid- and Aerodynamics; Magnetic properties and materials; Magnetic properties of nanostructures; Magnetism; Nuclear radiation; Physics; Physics and Astronomy; Regular Article; Solid State Physics; Topical issue: New Trends in Magnetism and Magnetic Materials; CoPt; Anisotropy Constant; FePt; Carbon Matrix; Magnetic Anisotropy Energy; Coordination number; Vienna ab initio simulation package; Annealing; Platinum alloys; Magnetic moments; Magnetic hysteresis; EXAFS; Nanoparticles; Local structure; Interatomic distances; Size effect; Density functional method; Embedded cluster method; Cobalt alloys; Synchrotron radiation; Atomic clusters; Transition element alloys
• ISSN: 1434-6028; 1434-6036
• DOI: 10.1140/epjb/e2013-30644-0

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 L1 0 -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 L1 0 CoPt bulk.