[1] Institute of Physics, Polish Academy of Science, 02-668, Warsaw, Poland
[2] Faculty of Physics, Low Temperature Department, M. V. Lomonosov Moscow State University, 119899 Moscow, Russia
[3] Institute of Molecular Physics, Russian Research Center Kurchatov Institute, 123182, Moscow, Russia
[4] Laboratoire de Chimie des Solides (CNRS), Batiment, 414, 91405 Orsay Cedex, France