Electron Spin Relaxation in Pseudo-Jahn–Teller Low-Symmetry Cu(II) Complexes in Diaqua(L-Aspartate)Zn(II)·H2O Crystals
✍ Scribed by S.K Hoffmann; W Hilczer; J Goslar; M.M Massa; R Calvo
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 138 KB
- Volume
- 153
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
Low
-temperature (4-55 K) pulsed EPR measurements were performed with the magnetic field directed along the z-axis of the g-factor of the low-symmetry octahedral complex [ 63 Cu(Laspartate) 2 (H 2 O) 2 ] undergoing dynamic Jahn-Teller effect in diaqua(L-aspartate)Zn(II) hydrate single crystals. Spin-lattice relaxation time T 1 and phase memory time T M were determined by the electron spin echo (ESE) method. The relaxation rate 1/T 1 increases strongly over 5 decades in the temperature range 4-55 K. Various processes and mechanisms of T 1 -relaxation are discussed, and it is shown that the relaxation is governed mainly by Raman relaxation processes with the Debye temperature Θ D = 204 K, with a detectable contribution from disorder in the doped Cu 2+ ions system below 12 K. An analytical approximation of the transport integral I 8 is given in temperature range T = 0.025-10 Θ D and applied for computer fitting procedures. Since the Jahn-Teller distorted configurations differ strongly in energy (δ 12 = 240 cm -1 ), there is no influence of the classical vibronic dynamics mechanism on T 1 . Dephasing of the ESE (phase relaxation) is governed by instantaneous diffusion and spectral diffusion below 20 K with resulting rigid lattice value 1/T 0 M = 1.88 MHz. Above this temperature the relaxation rate 1/T M increases upon heating due to two mechanisms. The first is the phonon-controlled excitation to the first excited vibronic level of energy ∆ = 243 cm -1 , with subsequent tunneling to the neighbor potential well. This vibronic-type dynamics also produces a temperature-dependent broadening of lines in the ESEEM spectra. The second mechanism is produced by the spin-lattice relaxation. The increase in T M is described in terms of the spin packets forming inhomogeneously broadened EPR lines.