1. Belarusian State University, Nezavisimosti ave. 4, 220030 Minsk, Belarus
2. Scientific and Practical Materials Research Center, National Academy of Sciences of Belarus P. Brovki Str. 17, 220072 Minsk, Belarus
3. Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena, Germany
4. Lublin University of Technology, Nadbystrzycka 38d, 20-618 Lublin, Poland