1. Applied Physics Department and Instituto de Investigacións Tecnolóxicas
2. Universidade de Santiago de Compostela
3. Spain
4. Department of Physics
5. University of York
6. York YO10 5DD
7. UK
8. Instituto de Ciencia de Materiales de Madrid
9. CSIC
10. ES-28049 Madrid
11. Faculty of System Science and Technology
12. Akita Prefecture University
13. Yuri-Honjo 015-0055
14. Japan