1. INN, NCSR Demokritos, Athens 15310, Greece
2. IFW Dresden, P.O. Box 270116, 01171 Dresden, Germany
3. TU Dresden, Institute for Materials Science, 01062 Dresden, Germany
4. Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece
5. Department of Physics, Pukyong National University, Busan 608-737, South Korea