1. Institute
of Physics and Applied Physics, Yonsei University, 134 Shinchon-dong, Seoul 120-749, Korea
2. Department
of Physics, Yonsei University, Wonju 220-710, Korea
3. School
Department of Material Science and Engineering, Sungkyunkwan University, Suwon 440-746, Korea
4. Division
of Materials Science, Korea Basic Science Institute, Daejeon 305-806, Korea