1. National Creative Research Initiative Center for Oxide Nanocrystalline Materials and School of Chemical Engineering, Seoul National University, Seoul 151-744, Korea, Department of Physics and Institute of Basic Sciences, Sungkyunkwan University, Suwon 440-746 Korea, Department of Physics and Pohang Acceleration Laboratory, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Korea, and New Material Evaluation Center, Korea Research Institute of Standards and Science, Taejon 305-600, Korea