CONTRIBUTIONS TO ZERO-FIELD SPLITTING FROM SPIN TRIPLETS OF 3D4 AND 3D6 IONS IN TETRAGONAL SYMMETRY

In this paper, the perturbation formulas for the zero-field splitting (ZFS) parameters of 3d4 and 3d6 ions in tetragonal symmetry are derive d taking into account all the excited spin-triplet states 3L (L = P,D, F,G,H), in the strong-field scheme. The contribution of the spin tripl ets to the ZFS and the validity of the 5D approximation for 3d4 ions a t tetragonal sites are investigated. The results show that the spin-tr iplet contribution to the ZFS is not negligible, and the validity of 5 D approxmation is highly limited in general, although a great deal of early studies of the ZFS for 3d4 and 3d6 ions in crystals were based o n the 5D approximation. Applications are made to Fe4+ ions in CdSiP2 a nd Cr2+ ions in Rb2CrClr, and the obtained results are in good agreeme nt with the experimental data. The contribution of spin triplets is fo und to be either comparable to or larger than that of 5D state in thes e crystals.