1. Institute for Single Crystals, National Academy of Sciences of Ukraine, 60 Nauki Ave., Kharkov 61072, Ukraine
2. V. N. Karazin Kharkov National University, 4 Svobody Sq., Kharkov 61022, Ukraine
3. B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47 Nauki Ave., Kharkov 61103, Ukraine