[1] Karlsruhe Inst Technol, Inst Inorgan Chem, D-76131 Karlsruhe, Germany
[2] Katholieke Univ Leuven, Div Quantum & Phys Chem, B-3001 Heverlee, Belgium
[3] Katholieke Univ Leuven, INPAC Inst Nanoscale Phys & Chem, B-3001 Heverlee, Belgium
[4] CNRS, Inst Neel, F-38042 Grenoble 9, France