1. Institute for Solid State Research, IFW Dresden, P. O. Box 270116, D-01171 Dresden, Germany
2. Institute of Metal Physics of National Academy of Sciences of Ukraine, 03142 Kyiv, Ukraine
3. Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
4. Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China