Theoretical investigations of the spin Hamiltonian parameters of ZrSiO4:Np4+

In this work, the spin Hamiltonian (SH) parameters g parallel and g perpendicularto, and the hyperfine structure constants A parallel and A perpendicularto for ZrSiO4:Np4+ are investigated on the basis of the perturbation formulas of these parameters for a 5f3 ion in tetragonal (D2d) symmetry. In these formulas, the contributions to the SH parameters from the second-order perturbation terms, the admixtures of various energy levels and the covalency effect are taken into account. The related crystal-field parameters are calculated from the superposition model and the local structural data of the Zr4+ site occupied by the impurity Np4+. The calculated SH parameters agree reasonably with the experimental data. The validity of the theoretical results is discussed. (orig.)