The theory of spin-correlated crystal fields: Application to Gd3+ in C3h symmetry

Application of the recently formulated theory of spin-correlated crystal fields is made to the Gd3+ ion in ethysulphate lattices. Detailed calculations of the spin-correlated crystal field contribution to the zero field splitting are found to be of the correct sign but its magnitude is too large. It is comjectured that similar types of mechanisms involving excitations to other sites may be responsible for the discrepancy.