[1] Physical Laboratory, Opole Technical University, ul. Ozimska 75, Opole 45-370, Poland
[2] Inst. of Low Temp./Struct. Research, Polish Academy of Sciences, ul. Okólna 2, 50-395 Wroclaw, Poland
[3] Department of Material Science, Silesian University of Technology, ul. Krasiñskiego 8, Katowice 40-019, Poland