Superposition-model analysis of the spin-strain coupling tensor in ruby

Expressions for the elements G_pq of the spin-strain coupling tensor have been derived for ruby (Al₂O₃:Cr³⁺) in terms of the superposition-model parameters describing the axially symmetric field of each ligand. Four intrinsic parameters, A₂, A₄ and their radial derivatives, provide a reasonable fit to the ten G_pq but the zero-field splitting D cannot be fitted and must be largely due to other mechanisms. The parameters obtained are used to estimate the elements of the G tensor in MgO:Cr³⁺ and these are compared with measured values.