ESR investigation of a spin 1/2 chlorine-associated defect in synthetic FeS₂ crystals

A new type of spin 1/2 chlorine-associated defect species has been observed by ESR in as-grown, sulfur-deficient FeS₂ crystals grown by the method of chemical vapor transport using ICl₃ as the transport agent. The ESR spectrum of this defect species exhibits a low symmetry and a weak hyperfine interaction with a single chlorine nucleus. The g-factor anisotropy indicates that this species is most likely a hole species, having a p⁵ electron configuration and localized at a sulfur atom. We assign this defect species as an (SCl)^2- impurity defect, replacing (S-S)^2- and locally associated with a Fe²⁺ vacancy created probably to compensate for the substitutional Cr³⁺ impurities.