1. High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577
2. Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames Iowa, U.S.A.
3. National Institute for Materials Sciences, 3-13 Sakura, Tsukuba, Ibaraki 305-0003
4. Institute for Materials Research, Tohoku University, Sendai 980-8577