1. Institut für Inorganic Chemistry, Georg-August-University Göttingen, Tammannstrasse 4, D-37077 Göttingen, Germany
2. Department of Physics, Universität Erlangen-Nürnberg, Erwin-Rommel-Strasse 1, D-91058 Erlangen, Germany
3. Leibniz-Institute for Solid State and Materials Research IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany