Proton concentration dependence of the proton spin-lattice relaxation time in copper tutton salts

Abstract

The proton spin-lattice relaxation time, T 1p, was measured in a series of single crystals of the Tutton salt: (Cu,Zn)Cs 2(SO 4) 2.6(H,D) 2O. The measurements were performed at fields in the region from 5 to 15 kOe and at liquid- helium temperatures. We investigated samples with 12, 25, 50 and 100% protons in the waters of hydration, all having a Cu 2+-concentration of about 0.5%. In these samples, the proton relaxation path is bottlenecked, under most experimental conditions, by the thermal contact between the proton Zeeman system and the electron dipole-dipole interaction system, provided by the proton three-spin process. This was always the case in our previously investigated 6%- 1H sample [1, 2]. For higher proton concentrations, however, the role of the electron spin-lattice relaxation in the proton relaxation path becomes more important. The results of the 50 and 100%- 1H sample at 1.3 K show clearly that at high fields the proton three-spin process bottlenecks the proton relaxation path, while with decreasing field the electron spin-lattice relaxation process takes over. Supplementary measurements in two samples with 12%- 1H and different Cu 2+-concentrations show a strong dependence of T 1p on this concentration. Finally, an attempt has been made to determine the role of the proton spin diffusion in the relaxation path.