1. Faculty of Education and Human Studies, Akita University, Akita 010-8502, Japan
2. Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A.
3. Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
4. Department of Applied Physics, School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan