1. Max-Planck Institut für Kohlenforschung, Mülheim an der Ruhr D-45470, Germany
2. Institute of General and Inorganic Chemistry, Bulgarian Academy of Science, Akad. Georgi Bontchev, Street 11, 1113 Sofia, Bulgaria
3. Department of Physics and National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States
4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States