Effects of chemisorption and alloying on the magnetism of nickel clusters

Results of self-consistent field-local spin density-scattered-wave calcualtions are reported for small cluster (13–14 atoms) containing nickel and copper atoms in various proportions and for these clusters interacting with a CO molecule adsorbed on a top or a hollow site. The effect of alloying on the magnetism of the clusters in similiar to that found in the bulk case, namely (i) the Ni magnetic moments decrease with Cu content and (ii) the spin polarization on the copper atoms is very small. The effect of Cu is mainly limited to the fist nearest-neighbot Ni atoms. In agreement with experiment, adsorption of CO on pure Ni clusters causes a decerese in the magnetic moments of nearby Ni atoms, and we have recently proposed a detailed mechanism which explains this effect. The influence of Co on Ni magnetism for NiCu + CO clusters is investigated and is shown to be the same as in the pure Ni case as long as no Cu atoms are present in the first coordination shell of the Ni atom(s) involved in the bond. If Cu atoms are present in the first coordination shell, the stabilization of the Ni potential by CO chemisorption leads to increased NiCu covalent interactions. For the cases we have examined, this modified NiCu binding leads to a small increase rather than the usual decrease of the Ni moment for the atom directly involved in the chemisorption.