1. Institute of Physics, Polish Academy of Science, al. Lotników 32/46, PL 02-668 Warszawa, Poland
2. Institute of Theoretical Physics, Warsaw University, PL 00-681 Warszawa, Poland
3. ERATO Semiconductor Spintronics Project, Japan Science and Technology Agency, al. Lotników 32/46, PL 02-668 Warszawa, Poland