Vibronic dynamics and electron spin relaxation of Cu(formate)4(H2O)2 complexes in dibarium zinc formate tetrahydrate, Ba2Zn(HCOO)6·4H2O single crystals

Abstract

Continuous wave and pulsed X-band electron paramagnetic resonance experiments have been performed for Cu2+ ions substituting Zn(II) in Ba2Zn(HCOO)6·4H2O single crystals in the temperature range 4.2–300 K. Spin-Hamiltonian parameters of octahedral Cu(HCOO)2(H2O)2 complexes at the rigid lattice limit (below 77 K) are the following: g z = 2.405, g y = 2.095, g x = 2.065, A z = 130, A y = 4, and A x = 11 × 10−4 cm−1. The parameters along the y and z-axes display vibronic averaging effects on heating which allows evaluation of the energy difference δ12 = 347 cm−1 between the two lowest energy Jahn–Teller distorted configurations. The electron spin-lattice relaxation is governed by Raman processes and the Debye temperature has been determined as Θ D = 204 K. The electron spin echo amplitude decay is determined by instantaneous diffusion below 10 K and then the dephasing rate weakly increases on heating because of libration motions of Cu2+ complexes and/or excitations to the first excited vibronic level of energy Δ = 63 cm−1.