1. Solid State Physics Department, University of Łódź, Pomorska 149/153, PL-90-236 Łódź, Poland
2. Institute of Mathematics, Polish Academy of Sciences, Łódź Branch, Banacha 22, PL-90-238 Łódź, Poland
3. Department of Relativity Physics, University of Warmia and Mazury, Słoneczna 54, PL-10-710 Olsztyn, Poland