Physical and chemical properties of Co n−m Cu m nanoclusters with n = 2–6 atoms via ab-initio calculations
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We present ab-initio density-functional calculations of the structural, magnetic, and chemical properties of cobalt–copper clusters (1 nm in size) with two to six atoms. We applied several search methods to find the most stable configurations for all stoichiometries. Particular attention is given to the relation between the geometric and magnetic structures. The clusters behavior is basically governed by the Co–Co interaction and to a lesser extent by the Co–Cu and Cu–Cu interactions. A tendency for Co-clumping is observed. Such information is quite relevant for segregation processes found in bulk Co–Cu alloys. For a given cluster size, magnetic moments increase mostly by 2μB per Co-substitution coming from the cobalt d-states, while for some cases s-electrons give rise to itinerant magnetism. Magnetic moment results are also consistent with the ultimate jellium model because of a 2D to 3D geometrical transition. The chemical potential indicates less chemical stability with the Co atoms, while the molecular hardness can be linked mostly to the ionization potential for these small clusters.
KeywordsCobalt–copper ferromagnetic nanoclusters Phase separation and segregation Magnetic properties of nanostructures Electronic structure of nanoscale materials Modeling and simulation
Support for this study from CNPq (Brasil) and CONICYT (Chile), Joint Project CIAM 490891/2008-0 is gratefully acknowledged. We also thank the Millennium Science Nucleus (Chile), Project P10-061-F; Doctorate Program PUC (Chile), Project 06/2009; FONDECYT (Chile), Project 1100365; and CAPES/PROCAD (Brasil) Project 059/2007. Computer time from the National Supercomputing Center CENAPAD CESUP/UFRGS is also acknowledged.