Magnetic susceptibility and compositional dependence of the energy gap in Cd1-xCoxTe

Single crystals of the diluted magnetic semiconductor Cd1-xCoxTe grown by the vertical Bridgman technique are characterized by wavelength-modulated reflectivity and magnetization measurements. Low-temperature magnetization and high-temperature magnetic susceptibility analysis were used to extract the exchange integrals for up to third-neighbour Co2+ pairs in the CdTe host: J(1)/(B) = -25+/-7 K, J(2)/k(B) = -3.0+/-1.5 K, and J(3)/k(B) = -1.3+/-0.3 K. These values correspond well to the values obtained for other Co-based II-VI diluted magnetic semiconductors and are a clear manifestation of the unusually large Co2+-CO2+ antiferromagnetic interaction. The excitonic energy gap E-g(x) of Cd1-xCoxTe in the wavelength-modulated reflectivity shows a linear monotonic increase with increasing x in the composition range studied.