[1] Univ Technol Troyes, ICD CNRS UMR STMR 6279, Lab Nanotechnol & Instrumentat Opt, F-10004 Troyes, France
[2] CNRS, CEA UMR12, Lab Leon Brillouin, Gif Sur Yvette, France
[3] CNRS, Inst Galilee, LSPM, F-93430 Villetaneuse, France
[4] Univ Paris 13, F-93430 Villetaneuse, France
[5] CNRS, Inst Neel, F-38042 Grenoble 9, France
[6] Univ Grenoble 1, F-38042 Grenoble 9, France