Investigations of the spin-Hamiltonian parameters for Er 3+ at the Th 4+ site in ThGeO 4

Abstract

The spin-Hamiltonian (SH) parameters g factors g ∥, g ⊥ and the hyperfine structure parameters A ∥ and A ⊥ for Er 3+ at the tetragonally distorted dodecahedral Th 4+ site in ThGeO 4 are theoretically investigated by using the perturbation formulas of the SH parameters for a 4f 11 ion in tetragonal symmetry. In these formulas, the contributions to the SH parameters from the second-order perturbation terms and the admixture of various energy levels are taken into account. The related crystal-field parameters are calculated from the geometrical relationship of the impurity center and the superposition model. Based on the studies, the lowest Kramers doublet is found to be Γ 7, rather than Γ 6 suggested in the previous work. The calculated SH parameters for Γ 7 doublet in this work are smaller than those obtained for Γ 6 doublet in the previous work and in good agreement with the observed values. The various contributions to the SH parameters are discussed.