1. Departments of Inorganic Chemistry and Solid State Physics, P. J. Safarik University, 04001 Kosice, Slovakia, Institute of Experimental Physics, Slovak Academy of Sciences, 04101 Kosice, Slovakia, DESY, Hasylab, Notkestrasse 85, D-22603 Hamburg, Germany, and Institute of Inorganic Chemistry AS CR, 25068 Rez, Czech Republic