1. Hitachi Cambridge Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
2. CEA/LETI-MINATEC, CEA-Grenoble, 17 rue
des Martyrs, F-38054 Grenoble, France
3. SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, 17 rue des Martyrs, 38054 Grenoble, France
4. Instituto
de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal
68528, 21941-972 Rio de Janeiro, Brazil
5. Cavendish
Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom