Relativistic density functional study of gold coated magnetic nickel clusters

Coating of magnetic clusters by gold atoms is becoming an experimental tech nique of increasing interest for passivation and stabilization of these sma ll metal particles. To computationally investigate the effect of gold coati ng, we have studied the magnetic clusters Ni-6 and Ni-13 employing an all-e lectron scalar-relativistic density functional method. We examine two serie s of octahedral clusters with increasing gold coverage of up to a monolayer : Ni6Aun (n = 0,8,32) and Ni13Aun (n = 0,6,8,14,24,30,42). Structural featu res, binding energies, and gold adsorption energies are determined and disc ussed. The different atomic radii of Au and Ni lead to rather short Au-Au a nd relatively long Ni-Ni distances in these clusters. The Au-Ni contacts ar e found to be the longest nearest-neighbor distances; a detailed analysis i ndicates these bonds to be the strongest in these Au-covered Ni clusters. T he atomization energies change only slightly with increasing Au coverage. A lso, the effect of gold adsorption on the magnetic properties of the Ni cor es is analyzed. For the Ni6Aun series the magnetism decreases with n, while for Ni13Aun a maximum cluster magnetization is calculated for incomplete g old coverage. This different behavior of the two cluster series can be trac ed to differing numbers of unpaired electrons per atom in the pure Ni clust ers and to an increased magnetic moment due to the adsorption of isolated A u atoms. Both series exhibit a residual magnetism at full monolayer coverag e of the Ni cores. (C) 2001 American Institute of Physics.