1. London Centre for Nanotechnology; University College London (UCL); London WC1H 0AH UK
2. Department of Chemistry; UCL; London WC1H 0AJ UK
3. Peter Grünberg Institut and Institute for Advanced Simulation; Forschungszentrum Jülich and JARA; 52428 Jülich Germany
4. School of Materials Science; Japan Advanced Institute of Science and Technology (JAIST); Nomi Ishikawa 923-1292 Japan
5. Institute for Solid State Physics; University of Tokyo; Kashiwanoha 5-1-5 Kashiwa Chiba 277-8581 Japan
6. Department of Physics and Astronomy; UCL; London WC1E 6BT UK