1. Contribution from the Institute of Inorganic and Analytical Chemistry, Justus-Liebig University Giessen, Heinrich-Buff-Ring 58, 35392 Giessen, Germany, Department of Physics and Material Sciences Center, Philipps University of Marburg, Renthof 5, 35032 Marburg, Germany, and Experimental Physics V, Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, Universitätsstrasse 2, 86135 Augsburg, Germany