Electron Spin Relaxation of Cu(II) Ions in ZnGeF6·6H2O Crystal with Strong Jahn–Teller Effect

Cu ions doped to ZnGeF6 · 6H2O substitute the host Zn ions and undergo a strong Jahn–Teller effect producing nearly axial elongation of the Cu(H2O)6 octahedra with equal population of the three possible deformations at low temperatures as shown by the EPR spectra. Reorientations between these distorted configurations are observed as a continuous shift of EPR lines leading to averaging of the gand A-tensors. The full averaging is observed at the phase transition temperature 200 K. Electron spin relaxation was measured up to 45 K only, where the electron spin echo signal was detectable. Electron spin–lattice relaxation is governed by the Raman two-phonon process allowing to determine the Debye temperature as ΘD = 99 K. There is no contribution of the Jahn–Teller dynamics to the spin–lattice relaxation rate. Electron spin echo decay is strongly modulated by dipolar coupling to the H and F nuclei. The phase memory time is governed by instantaneous diffusion at helium temperatures and then by spin–lattice relaxation processes and excitation to the first vibronic level of energy ∆ = 151 cm−1.