1. Université de Bordeaux, LOMA, UMR 5798, F-33400 Talence, France CNRS, LOMA, UMR 5798, F-33400 Talence, France
2. Grup
de Caracterització de Materials, Department de Física
i Enginyeria Nuclear, ETSEIB, Diagonal 647, Universitat Politècnica de Catalunya, 08028 Barcelona, Catalonia, Spain
3. B. Verkin Institute for Low Temperature Physics and Engineering of NAS Ukraine, 47 Lenin Ave., Kharkov 61103, Ukraine
4. Institute
of Low Temperature and Structure Research, Polish Academy of Sciences, ul. Okólna 2, 50-422 Wroclaw, Poland