1. H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS81TL, UK.
2. Laboratoire National des Champs Magnétiques Pulsés (LNCMP), UMR CNRS-UPS-INSA 5147, Toulouse 31400, France.
3. Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
4. Department of Advanced Materials Science, Graduate School of Frontier Science, University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa-shi, Chiba 277-8651, Japan.