Magnetic susceptibility and compositional dependence of the energy gap in Cd<SUB>1-x</SUB>Co<SUB>x</SUB>Te

Single crystals of the diluted magnetic semiconductor Cd<SUB>1-x</SUB>Co<SUB>x</SUB>Te grown by the vertical Bridgman technique are characterized by wavelength-modulated reflectivity and magnetization measurements. Low&#8722; temperature magnetization and high-temperature magnetic susceptibility analysis were used to extract the exchange integrals for up to third-neighbour Co<SUP>2+</SUP>pairs in the CdTe host: J<SUB>1</SUB>/k<SUB>B</SUB> = -25pm7 K, J<SUB>2</SUB>/k<SUB>B</SUB>= -3.0pm1.5 K, and J<SUB>3</SUB>/kB = -1.3pm0.3 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 Co<SUP>2+</SUP>-Co<SUP>2+</SUP> antiferromagnetic interaction. The excitonic energy gap Eg(x) of Cd<SUB>1-x</SUB>Co<SUB>x</SUB>Te in the wavelength-modulated reflectivity shows a linear monotonic increase with increasing x in the composition range studied