Abstract:Based on the crystal field theory, the anisotropic g factors g _iiand the hyperfine structure constants A _iifor (NH ₄) ₂Mg(SO ₄) ₂·6H ₂O:Cu ²⁺are theoretically investigated by using the high-order perturbation formulas of these electron paramagnetic resonance (EPR) parameters for a 3d ⁹ion in rhombically ( C _4v) elongated octahedra. In the calculated formulas, the crystal field parameters are set up from the superposition model and the admixture of d-orbitals in the ground state wave function is taken into account. According to the calculations, the local structure values Cu(H ₂O) ₆ ²⁺clustering in (NH ₄) ₂Mg(SO ₄) ₂·6H ₂O crystal are: R _x≈0.1872 nm, R _y≈0.2033 nm, R _z≈0.2292 nm; and the mixing coefficients of the ground state wave function parameters αand βare 0.995 and 0.0999, respectively. The calculated results show good agreement with the experimental data, and the reasonableness of these results is discussed.