ZERO-FIELD SPLITTING IN TRANSITION METAL IONS

Abstract

“The origin of the zero-field splittings of the orbitally non-degenerate ground states of the transition metal ions ($3d^{2}, 3d^{3}$ and $3d^{24}$ solutes) has been studied on the assumption that these splittings are due to the combined action of an electric field gradient and the spin-spin interaction. A relation between the splitting parameters D and E of the conventional spin-Hamiltonian and the field gradients $q\|$ and $ \eta q\|$ respectively has been deduced on the above basis using hydrogenic wave functions and $d \rightarrow d, d \rightarrow g$ and $d \rightarrow $s excitations. A reasonably good agreements with the splittings has been obtained for $Mn^{2+}$ in corundum but an apparent disagreement has been found for $Fe_{3+}$ in $Al_{2}O_{3}$, considering the known values of the field gradients in these cases. For $Cr^{3+}(d^{3}$ solute) in corundum, the major sources of splittings seem to be the spinorbit interaction and the distortion of the ground state wave functions due to co-valent $\pi$-bounding and not the spin-spin interaction. The cause of the apparent disagreement for $Fe_{3+}$ in $Al_{2}O_{3}$ is discussed. A definite understanding of the cause of the zero-field splittings in the transition metal ions depends on more accurate knowledge of the field gradients acting on these ions is different crystalline environments.”