1. Sumy State University, 2 Rymskogo-Korsakova Str., 40000 Sumy, Ukraine
2. G.V. Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky Blvd., UA-03680 Kyiv-142, Ukraine
3. V.N. Karazin Kharkiv National University, 4 Svobody Sq., 61022 Kharkiv, Ukraine