1. O.O. Galkin Donetsk Physics-Technology Institute of the National Academy of Sciences of Ukraine, 46 Nauki Ave., Kyiv, Ukraine
2. Yaroslav-the-Wise Novgorod State University, 41 Bolshaya St. Petersburg Str., Veliky Novgorod 173003, Russia
3. Ukrainian Engineering Pedagogical Academy, 16 Universytetska Str., Kharkiv 61003, Ukraine
4. Institute of Solid State Physics RAS, 2 Academician Ossipyan Str., Chernogolovka 142432, Russia