1. Department of Technical Physics, L.N. Gumilyov Eurasian National University, Satpayev Str. 2, Astana 010008, Kazakhstan
2. Institute of Physics and Technology, Ural Federal University, 19 Mira str., Yekaterinburg 620002, Russia
3. Institute of Solid State Physics, University of Latvia, Kengaraga str. 8, LV-1063 Riga, Latvia