EPR, Electron Spin–Lattice Relaxation, and Debye Temperature of Cu(II)-Doped Triglycine Selenate Crystal

Single-crystal rotational data of CW-EPR and two-pulse field-swept ESE collected at room and low temperatures lead to the spin-Hamiltonian parametersg_z= 2.2596,g_y= 2.0647,g_x= 2.0529,A_z= 151.2 × 10⁻⁴cm⁻¹,A_y= 2.5 × 10⁻⁴cm⁻¹, andA_x= 42.2 × 10⁻⁴cm⁻¹which are temperature independent. The parameters and Cu²⁺ion site in the crystal unit cell are very similar to those in the triglycine sulfate crystal. Electron-spin-echo measurements of the spin–lattice relaxation timeT₁in the temperature range 4.2–90 K gave identical results for inversion- and saturation-recovery methods, indicating a negligible spectral-diffusion contribution. TheT₁decreases from 275 μs at 15 K to 1.7 μs at 83 K and the temperature dependence is governed by the direct (one-phonon) process at low temperatures and two-phonon Raman process at higher temperatures. A new analytical form of theI₈transport integral of the Raman term is proposed. The best fit to the theoretical expression was found for the Debye temperature ϑ_D= 168 ± 3 K which is comparable to ϑ_D= 171 K calculated from the elastic constants of the crystal.