1. Department of Physics, University of Osijek, Trg Ljudevita Gaja 6, HR-31000 Osijek, Croatia
2. Institute for Materials Research-UNAM, Ciudad Universitaria Coyoacan, C.P. 04510 Mexico D.F., Mexico
3. Faculty of Science, University of Sarajevo, Zmaja od Bosne 35, 71000 Sarajevo, Bosnia and Herzegovina
4. Department of Physics, Faculty of Science, Bijenička Cesta 32, HR-10002 Zagreb, Croatia
5. Institute of Physics, Bijenička Cesta 46, P.O. Box 304, HR-10001 Zagreb, Croatia