1. P. J. Šafárik University in Košice Faculty of Science Park Angelinum 9 04154 Košice Slovakia
2. Department of Physics Uzhgorod National University Uzhgorod 88000 Ukraine
3. Materials Science Division and Center for Nanoscale Materials Argonne National Laboratory, Argonne Illinois 60439
4. Institute of Materials Research Slovak Academy of Sciences 04001 Slovakia