1. See E. Nagaev, Physics of Magnetic Semiconductors (MIR Publishers, Moscow, 1983).
2. P. Wolff and J. Warnock, J. Appl. Phys. 55, 2300 (1984).
3. A. Golnik, J. 6aj, M. Nawrocki, R. Planel, and C. Benoit á la Guillaume, Proc. XV Intl. Conf. Phys. Semiconductors, Kyoto, 1980 (J. Phys. Soc. Japan, Suppl. A49, pg. 819); M. Nawrocki, R. Planel, G. Fishman and R. Galazka, ibid, pg. 823.
4. A. Golnik, J. Ginter and J. Gaj, J. Phys. C16, 6073 (1983).
5. T. Dietl and J. Spalek, Phys. Rev. Letters 48, 355 (1982)