1. SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, Grenoble, F-38054, France
2. IMR, Tohoku University, Oarai, Ibaraki 311-1313, Japan
3. Laboratoire National des Champs Magnetiques Intenses, UPR 3228, CNRS-UJF-UPS-INSA, 143 Avenue de Rangueil, 31400 Toulouse, France
4. Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan