Magnetism in small Pd clusters

We report a theoretical study of the magnetic behavior of selected free-standing Pd-N clusters (N less than or equal to 55) with fcc shapes. Particular attention is devoted here to the fcc structures taking into account recent experimental observations for Pd nanoparticles [Phys. Rev. Lett. 91 (2003) 197201; Phys. Rev. Lett. 91 (2003) 237203]. The optimized geometrical structures were obtained from an uniform relaxation of the cubo-octahedral and the truncated-octahedral configurations using the embedded atom method (EAM). The spin-polarized electronic structure and related magnetic properties of those optimized geometries were calculated by solving self-consistently a spd tight-binding Hamiltonian. We obtain very weak magnetic moments in a qualitative agreement with the early experiments, with those of Sampedro et al. and with most of the theoretical results concerning the negligeable local magnetic moments in low-dimensional Pd systems. We explore the recently observed tendency of certain sites to be more ma--netic than the rest of the cluster. Our results are discussed in the context of several experiments where some controversy still exists regarding the onset of magnetism and its magnitude. (C) 2004 Elsevier B.V. All rights reserved.