1. Institute of Materials Science, Federal University of Sao Francisco Valley, 48920-310 Juazeiro, BA, Brazil
2. CEMUC, Electrical and Computers Engineering Department, Faculty of Sciences and Technology of The University of Coimbra, Polo 2, Pinhal de Marrocos, 3030-290 Coimbra, Portugal
3. Physics Department, Technological Institute of Aeronautics (ITA), Praça Marechal Eduardo Gomes 50, 12228-900 São José dos Campos, SP, Brazil