Hyperfine structure of EPR spectra of Gd3+ odd isotopes in PbMoO4, Pb5Ge3O11, YVO4, and quadrupole interaction (temperature dependence)

A hyperfine structure of EPR signals of odd isotopes Gd³⁺ in Pb₅Ge₃O₁₁, PbMoO₄, and YVO₄ single crystals has been investigated at different temperatures. The observation of forbidden (with the nuclear spin flip) transitions has made it possible to determine quadrupole interaction P ₂ ⁰ associated with the gradient of the electric field of ligands at the impurity. It has been shown for the first time that, under the condition |P ₂ ⁰ | ≥ |A _{x, y} | (A _i are the tensor components), not only the magnitudes of splitting but also the observed asymmetry in a hyperfine structure (in perpendicular orientations of the magnetic field) depends on mutual signs of parameters of initial splitting b ₂ ⁰ and P ₂ ⁰ . Results of studying the spectra have demonstrated that |b ₂ ⁰ (T)|/|P ₂ ⁰ (T)| ～ const for a concrete single crystal, which assumes the similarity of physical mechanisms determining these parameters.