Anharmonic Effects in the Electron Spin-Lattice Relaxation of Radiation Defects in Potassium Selenate and Rochelle Salt Single Crystals

Abstract

An anharmonic character for the Raman processes of the electron spin--lattice relaxation of paramagnetic defect centres in γ-irradiated potassium selenate and Rochelle salt single crystals was observed at low temperatures.

Suppression of Raman electron spin relaxation of radicals in crystals. Comparison of Cu2+and free radical relaxation in triglycine sulfate and Tutton salt single crystals

“…The energy of the local phonon mode is low for all three radicals indicating that this mode lies within the acoustic phonon energies of the host crystal. The low energy local phonons were also found for free radicals in Rochelle salt crystals, where 1/T 1 = 7.4 cosech 2 (17.5/2kT) [28], for SeO − 3 in K 2 SeO 4 , where 1/T 1 = 185cosech 2 (27/2kT) [28], for PO 2− 3 in betaine phosphate, where 1/T 1 = 215cosech 2 (86/2kT) [22] and for S − 3 radical in zeolite A, where 1/T 1 = 35 000 cosech 2 (37/2kT) [24]. The c-coefficient values are also relatively small.…”

“…We show this for radicals produced by ionizing irradiation in two crystals. However, this is generally observed and can be recognized by an inspection of published relaxation data for various radicals in various solids (see the review of radical relaxation by Bertini et al [13] and papers [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]). There are a few exceptions: (a) spin relaxation of F-centres in alkali halides was well explained by a pure Raman process [30] and (b) the Raman process was considered as one of the contributions to the relaxation rate [31][32][33].…”

Theory of the Relaxation Processes for Multilevel Spin Systems in Dilute Paramagnetic Solids at High Temperature

“…Thus, the theoretical considerations of the anharmonic effects will conduct to a complex temperature dependent expression for the spin±lattice relaxation rates. So, the anharmonic effects have been found to be important for the Raman processes of the electron spin±lattice relaxation of paramagnetic defect centres [23]. However, the anharmonicity is expected to have more striking effects on a large amplitude resonance mode [17], or on a relaxaTheory of Relaxation Processes for Multilevel Spin Systems tional soft mode [24] than on the normal modes of the lattice.…”

Resonance local phonon mode and electron spin-lattice relaxation of formate-type free radicals studied by electron spin echo in Cd(HCOO)2·2H2O crystal

“…Because of very low radical concentration a detection of such modes by spectroscopic method or inelastic neutron scattering is not possible. Tartrate radical 24 [53]…”

“…It can be described as a damped harmonic oscillator. Spin-lattice relaxation via localized phonons of energy Δ L with Δ L > Θ D have been theoretically considered [46][47][48][49] and identified experimentally in various solids [47,[50][51][52][53][54][55][56][57]. However, in most theoretical approaches the low temperature dependence of…”