1. Department of Physics, Graduate School of Science, Kobe University, Kobe 657-8501, Japan
2. Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, SK-841 04, Bratislava, Slovakia
3. Institute of Physics, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 11, Bratislava, Slovakia
4. Department of Material Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan