FE-BASED SEMIMAGNETIC SEMICONDUCTORS WITH 2 ANIONS

(Cd1-xFex) (Te1-ySey) crystals have been studied both theoretically an d experimentally. In such a system, a part of Fe2+ ions are located in crystal environments of a lowered symmetry. The energy level structur e of these ions is substantially modified with respect to that of the Fe2+ ion in one-anion (ternary) crystal. Regarding magnetic properties , the most essential modification occurs when an Fe2+ ion is surrounde d by three atoms of Te and one Se atom. Then, a doublet becomes a grou nd state of the magnetic ion, while, in the case of a ternary crystal, the ground state of an Fe(2+)ion is always a nonmagnetic singlet. In consequence, for two-anion systems, we observe a Curie-like paramagnet ism instead of an otherwise revealed temperature independent (T less t han or equal to 10 K) Van Vleck paramagnetism. Although, in the presen t work, we are concerned mostly with (Cd1-xFex)(Te1-ySey), a similar b ehavior is also observed for various crystals based on zinc and mercur y. The results of our photoconductivity measurements indicate that the ground energetic state of an Fe2+ ion can take several localizations in the band structure of the matrix crystal. A specific position depen ds on a configuration of nearest neighbors of an Fe2+ ion, i.e., if it is surrounded by four Te, or three Te and one Se, etc. Concluding, we show that doped with Fe quaternary II-VI semimagnetic semiconductors demonstrate magnetic and optical properties essentially different from that of Fe doped ternary II-VI semimagnetic semiconductors.