1. Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal
2. IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
3. Department of Physics, Madanapalle Institute of Technology & Science, Madanapalle 517325, Andhra Pradesh, India
4. National Institute of Materials Physics, 105 bis Atomistilor, 077125 Magurele, Romania
5. Faculty of Science and Technology and MESA+ Institute for Nanotechnology, Inorganic Materials Science, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands
6. Department of Physics and CICECO-AIM, University of Aveiro, 3810-193 Aveiro, Portugal