1. National Institute for Materials Science,1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
2. Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21945-970 Rio de Janeiro, Brazil
3. Centro de Educação e Saúde, Universidade Federal de Campina Grande, Cuité, PB 58175-000, Brazil
4. Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany
5. Faculty of Physics, M V Lomonossov Moscow State University, 119991 Leninskie Gory, Moscow, Russia