1. Institute of Applied Physics, University of Hamburg, 20355 Hamburg, Germany
2. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, United States
3. Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka 940-2188, Japan
4. Walter Schottky Institut and Physik Department, Technische Universität München, 85748 Garching, Germany
5. Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan
6. Polymer and Fiber System Engineering, Chonnam National University, 77 Yongbong-ro, buk-gu, Gwangju 500-757, Korea