1. Institute of Physics, Faculty of Sciences, P.J. Safarik University, Park Angelinum 9, 041 54 Košice, Slovakia
2. FBERG, Technical University of Kosice, Kosice 04001, Slovakia
3. Institute of Materials Research, Slovak Academy of Sciences, Kosice 04001 Slovakia
4. Dept. Inorg. Chem., Fac. Sci., UPJS, Moyzesova 11, Kosice 04154, Slovakia