Axial parameter D of octahedral S-state ions in garnets

The values of the spin-hamiltonian parameters are reported for systems Fe³⁺:Ca₃Sc₂Ge₃O₁₂, Fe³⁺:Na₃Sc₂V₃O₁₂ and Mn²⁺:Na₃Sc₂V₃O₁₂. The values of the axial parameterD together with the values ofD compiled from literature are used in the discussion of the origin ofD. A close correlation ofD with the trigonal deformation of the octahedron of S-state ion indicates the importance of the covalency effects. On the other hand, it is shown thatD can be hardly understood on the basis of the relativistic model only.We are indebted to Dr. B. V.Mill of Moscow State University (USSR) for supplying the single crystals of Na₃Sc₂V₃O₁₂ and Ca₃Sc₂Ge₃O₁₂ garnets.