1. Pavol Jozef Šafárik University in Košice, Faculty of Science, Department of Condensed Matter Physics, Park Angelinum 9, 040 01 Košice, Slovakia
2. Slovak Academy of Science, Institute of Experimental Physics, Watsonova 47, 040 01 Košice, Slovakia
3. Pavol Jozef Šafárik University in Košice, Faculty of Science, Department of Inorganic Chemistry, Moyzesova 11, 040 01 Košice, Slovakia