EPR parameters and local geometry for Cr3+ and V2+ ions in HfS2 crystals

From the high-order perturbation formulas of EPR parameters (zero-field splitting D, g factors g∥, g⊥ and hyperfine structure constants A∥, A⊥) based on the two spin-orbit coupling parameter model for 3d3 ions in trigonal symmetry, the EPR parameters of Cr3+ and V2+ ions in HfS2 crystals are calculated. From the calculations, it is found that the local trigonal distortion angle θ of impurity center in HfS2:Cr3+ is smaller than that in HfS2:V2+. The dominant cause of the small zero-field splitting |D| and g-anisotropy |Δg| = |g∥ − g⊥| in HfS2:Cr3+ (compound to HfS2:V2+) is due to the small local trigonal distortion angle θ rather than to the small impurity-ligand distance R in HfS2:Cr3+.