Fe-based semimagnetic semiconductors with two anions.

Abstract

(${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$)(${\mathrm{Te}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Se}}_{\mathit{y}}$) crystals have been studied both theoretically and experimentally. In such a system, a part of ${\mathrm{Fe}}^{2+}$ ions are located in crystal environments of a lowered symmetry. The energy level structure of these ions is substantially modified with respect to that of the ${\mathrm{Fe}}^{2+}$ ion in one-anion (ternary) crystal. Regarding magnetic properties, the most essential modification occurs when an ${\mathrm{Fe}}^{2+}$ ion is surrounded by three atoms of Te and one Se atom. Then, a doublet becomes a ground state of the magnetic ion, while, in the case of a ternary crystal, the ground state of an ${\mathrm{Fe}}^{2+}$ ion is always a nonmagnetic singlet. In consequence, for two-anion systems, we observe a Curie-like paramagnetism instead of an otherwise revealed temperature independent (T\ensuremath{\le}10 K) Van Vleck paramagnetism. Although, in the present work, we are concerned mostly with (${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$)(${\mathrm{Te}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Se}}_{\mathit{y}}$), a similar behavior is also observed for various crystals based on zinc and mercury. The results of our photoconductivity measurements indicate that the ground energetic state of an ${\mathrm{Fe}}^{2+}$ ion can take several localizations in the band structure of the matrix crystal. A specific position depends on a configuration of nearest neighbors of an ${\mathrm{Fe}}^{2+}$ 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. \textcopyright{} 1996 The American Physical Society.