Zero-field splitting ofMn2+ions in scheelites

The spin-Hamiltonian parameters of the ${}_{}{}^6{}_{}{}^{}S$ ground state of ${\mathrm{Mn}}^{2+}$ have been measured for seven crystals with scheelite structure in the temperature range 4.2-350 K. The low-temperature values of the zero-field parameters reflecting the contributions from the static lattice are discussed with respect to the usual theories of $S$-state splitting. The applicability of the superposition model and of different point-charge models is revised. In this particular case the dominant part of the crystal-field contributions can be explained by a relativistic splitting mechanism. The appropriate crystal-field coefficients required are obtained by numerical calculations, the corresponding point charges being related to simple aspects of chemical bonding.