1. INAC, SPSMS, CEA Grenoble, 38054 Grenoble, France
2. Institut Néel, CNRS/UJF Grenoble, 38042 Grenoble, France
3. Department of Physics, Kobe University, Kobe 657-8501, Japan
4. Karlsruher Institut für Technologie, Institut für Festkörperphysik, 76021 Karlsruhe, Germany
5. Laboratoire National des Champs Magnétiques Intenses, UPR 3228, CNRS-UJF-UPS-INSA, 143 Avenue de Rangueil, 31400 Toulouse, France