1. Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25 Avenue des Martyrs, 38042 Grenoble, France
2. Laboratoire J.-A. Dieudonné, Université de Nice, Parc Valrose, 06108 Nice cedex 2 France
3. Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, United Kingdom