1. Faculty of Physics and Technical Sciences, L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
2. Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Lv-1063 Riga, Latvia
3. Department of Physics and Nanotechnology, Karaganda Buketov University, Karaganda 100028, Kazakhstan
4. The Department of Physics and Methods of Teaching Physics, Berdyansk State Pedagogical University, 71100 Berdyansk, Ukraine