1. B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47 Nauky Ave., Kharkiv 61103, Ukraine
2. Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FIN-20014 Turku, Finland and Turku University Centre for Materials and Surfaces (MatSurf), FIN-20014 Turku, Finland