Magnetic properties of small cobalt-copper clusters

Accurate first-principle calculations on bimetallic cobalt-copper clusters of up to six atoms (Perez et al 2012 J. Nanopart. Res. 14 933) revealed a close similarity of the ground-state magnetic properties to the ultimate jellium model, provided that a 2D to 3D geometric transition was invoked. We discuss this relationship in terms of partial occupancies of the valence electrons in both cases, with the jellium results described by nonperturbative spherical wavefunctions. Based upon this, we propose a scheme to predict magnetic properties of cobalt-copper clusters of up to twenty atoms using arguments of dimensionality and charge localization, and confirm some of these results with other independent density-functional calculations and experimental available data. The comparison with experiments is carried out for neutral and singly ionized cobalt clusters. Furthermore, a many-body tight-binding pseudopotential is used with Monte Carlo techniques to verify the stability of these new first-principle solutions.