1. Department of Solid State Physics, Polish Academy of Sciences, Wandy 3, 41-800 Zabrze, Poland
2. CEMES-LOE/CNRS, 29 rue J. Marvig, BP 4347, 31055 Toulouse Cedex, France
3. Laboratoire de Cristallographie, UPR CNRS 503, BP 166X, 38042 Grenoble Cedex, France