A variable temperature EPR study of Cu²⁺ doped single crystals of pyrovanadates β-Mg<inf>2</inf>V<inf>2</inf>O<inf>7</inf>, α-Zn<inf>2</inf>V<inf>2</inf>O<inf>7</inf>: Estimations of non-coincident g²-and ò-tensors

© Kazan Federal University (KFU). Full angular variations of Cu2+ EPR spectra in β-Mg2V2O7 (MgVO) and α-Zn2V2O7 (ZnVO) were recorded for orientations of external magnetic field in three mutually perpendicular planes at 120 K and 295 K, as well as in temperature range from 110 to 295 K at some chosen orientations of magnetic field. The principal values of the g2- and Ã2-tensors, as well as the orientations of their principal axes were determined from angular variations of EPR line positions in three mutually perpendicular planes, using a rigorous least square fitting procedure, especially adapted to the case of non-coincident principal axes of the Ã2-tensors for the monoclinic and triclinic point-group symmetries in MgVO and ZnVO crystals, respectively. This procedure uses the eigenvalues and eigenvectors of the spin-Hamiltonian matrix, which allows to determine the orientations of the principal axes of the g2 (Zeeman) and Ã2 (hyperfine-interaction)-tensors. It is found, that the principal values of g2- and Ã2-tensors of the Cu2+ ions are similar in the two crystals; however, the orientations of the principal axes of these tensors are significantly different from each other. This is because the Cu2+ ion in MgVO is 6-fold coordinated, whereas it is 5-fold coordinated in trigonal bipyramidal coordination in ZnVO. The principal values of the g2-tensor, so obtained, are exploited to determine the electronic ground state of the Cu2+ ion in these two crystals