Spin-Hamiltonian parameters of Zn1-xCrxS and Zn1-xCrxTe

The Hamiltonian matrices for the spin-quintet and spin-triplet states of 3d4 and 3d6 ions are constructed using a molecular orbital approach, including the electrostatic Coulomb term, tetragonal crystal field as well as the spin-orbit and spin-spin coupling. The spin-Hamiltonian parameters for Cr2+ ions in ZnS and ZnTe are interpreted using this approach. Correct signs and magnitude of the zero-field splitting parameter b20 2+ and b20 > 0 for ZnTe:Cr2+ are obtained including the contributions from the spin-orbit coupling within ligands S or Te. The present values of b40 and b44 in ZnS:Cr2+ are also improved as compared with the previous results. The good agreement between the calculated and the experimental values shows that the contributions to the zero-field splitting from the spin-triplet states of the central ions Cr2+ and the spin-orbit coupling of the ligands S (especially) and Te are important.