1. Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
2. Experimentelle Physik 2, Technische Universität Dortmund, 44227 Dortmund, Germany
3. Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw, Poland
4. International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw, Poland