Ligand-field model for the spin–lattice coupling coefficients of Mn in ZnS and ZnSe

Abstract

A ligand-field model is used to compute the spin–lattice coupling coefficient C11 to strains of symmetry EΘ of the fundamental state 6A1 of Mn in cubic ZnS and ZnSe. It is shown that the proposed ligand-field model in which C11 is given by a second-order perturbation scheme involving the molecular spin–orbit interaction between the fundamental state 6A1 and the three orbital triplet states 4T1 at lower energy gives theoretical values which correctly account for the experimental results. A detailed study is made of the strain-induced variations of the crystal electrostatic field, the metal–ligand, and ligand–ligand group overlap integrals and the molecular spin–orbit interaction. It is shown that in ZnS the strain-induced variation of the crystal electrostatic field is almost completely compensated by the strain-induced variations of the group overlap integrals and the molecular spin–orbit interaction thus explaining the small experimental value for C11 in this compound. In ZnSe the contributions of the strain-induced variation of the group overlaps and of the molecular spin–orbit interaction are preponderant.