[1] Instituto Federal de São Paulo, Campus São Carlos, São Carlos, SP,13565-905, Brazil
[2] Departamento de Física, Universidade Federal de São Carlos, São Carlos, SP,13565-905, Brazil
[3] CNR-SPIN, C/O Università degli Studi di Salerno, Fisciano (Sa),I-84084, Italy
[4] Dipartimento di Fisica E.R. Caianiello, Università degli Studi di Salerno, Fisciano (Sa),FI-84084, Italy
[5] Department of Physics, University of Oslo, POB 1048, Blindern, Oslo,0316, Norway
[6] Experimental Physics of Nanostructured Materials, Q-MAT, CESAM, Université de Liège, Sart Tilman, Liège,B-4000, Belgium