1. National Academy of Sciences of Ukraine, B. I. Verkin Physico–Technical Institute of Low Temperatures, pr. Lenina 47, 61103 Kharkov, Ukraine
2. International Laboratory of High Magnetic Fields and Low Temperatures, P.O. Box 4714, 50–985 Wrocław 47, Poland
3. Polish Academy of Sciences, W. Trzebiatowski Institute of Low Temperature and Structure Research, P.O. Box 1410, 50–950 Wrocław 2, Poland
4. Silesian University, A. Chełkowski Institute of Physics, ul. Uniwersytecka 4, 40–007 Katowice, Poland