Magnetic moments of chromium-doped gold clusters: the Anderson impurity model in finite systems.

The magnetic moment of a single impurity atom in a finite free electron gas is studied in a combined x-ray magnetic circular dichroism spectroscopy, charge transfer multiplet calculation, and density functional theory study of size-selected free chromium-doped gold clusters. The observed size dependence of the local magnetic moment can be understood as a transition from a local moment to a mixed valence regime. This shows that the Anderson impurity model essentially describes finite systems even though the discrete density of states introduces a significant deviation from a bulk metal, and the free electron gas is only formed by less than 10 electrons.

Photoelectron imaging spectroscopy of the small sodium cluster anions Na3(-), Na5(-), and Na7(-).

We present a photoelectron imaging study of the small sodium cluster anions Na3(-), Na5(-), and Na7(-) at photon energies in the visible and near UV range (hv = 1.64-4.28 eV).

Spin coupling and orbital angular momentum quenching in free iron clusters.

Magnetic spin and orbital moments of size-selected free iron cluster ions Fe{n}{+} (n=3-20) have been determined via x-ray magnetic circular dichroism spectroscopy. Iron atoms within the clusters exhibit ferromagnetic coupling except for Fe{13}{+}, where the central atom is coupled antiferromagnetically to the atoms in the surrounding shell. Even in very small clusters, the orbital magnetic moment is strongly quenched and reduced to 5%-25% of its atomic value while the spin magnetic moment remains at 60%-90%.

Photoelectron spectroscopy of silicon doped gold and silver cluster anions.

Photoelectron spectra of low temperature silicon doped gold cluster anions Au(n)Si(-) with n = 2-56 and silver cluster anions Ag(n)Si(-) with n = 5-82 have been measured. Comparing the spectra as well as the general size dependence of the electron detachment energies to the results on undoped clusters shows that the silicon atom changes the apparent free electron count in the clusters. In the case of larger gold clusters (with more than about 30 gold atoms) the silicon atom seems to consistently delocalize all of its four valence electrons, while in the case of the silver clusters a less uniform behavior is observed.