1. Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań, Poland
2. W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław, Poland
3. Institut fur Festkörper- und Werkstofforschung Dresden, Postfach 270016, 01171 Dresden, Germany