1. The Department of Physics and Methods of Teaching Physics, Berdyansk State Pedagogical University, 71100 Berdyansk, Ukraine
2. Engineering Profile Laboratory, L.N. Gumilyov Eurasian National University, Satpaev Str. 5, Astana 010008, Kazakhstan
3. Laboratory of Solid State Physics, Institute of Nuclear Physics, Almaty 050032, Kazakhstan
4. Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., LV-1063 Riga, Latvia