1. Tula State University, 92 Lenin Ave., 300012 Tula, Russia
2. B.I. Verkin Institute for Low Temperature Physics and Engineering, NAS of Ukraine, 47 Nauky Ave., 61103 Kharkiv, Ukraine
3. M. Kotsiubynsky Vinnytsia State Pedagogical University, 32 Ostrozhskogo Str., 21100 Vinnytsia, Ukraine