The temperature dependence of the 35Cl NQR spin-spin relaxation times TzQ in Mg(D,O),SnCI, and Ni(H,O),SnCI, is measured. Tza of the former compound is determined mainly by the magnetic dipolar field at the chlorine nucleus produced by the intramolecular nuclei, the tin nucleus, and five other chlorine nuclei in the [SnCI,]'~ ion. TzQ of the latter compound is governed mainly by the local magnetic field at the chlorine site produced by the intramolecular nuclei and unpaired electrons in the Ni2+ ions. The correlation time for electron-spin flips due to the exchange interaction among neighbouring unpaired electrons is evaluated from TzQ. A general behaviour of halogen NQR TZQ in diamagnetic and paramagnetic insulators is summarized.
IntroductionThe fluctuation of local magnetic field and the electric field gradient (EFG) at the resonant nucleus caused by thermal motions of atoms or molecules is one of the major relaxation mechanisms in nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR). The adiabatic (secular) and non-adiabatic (non-secular) components of the fluctuation contribute to the spin-spin relaxation time T,, while only the latter one contributes to the spin-lattice relaxation time TI [l]. T, does not alter with temperature as much as Tl and also T, is much shorter than T,, as long as the adiabatic term dominates over the non-adiabatic one.The spin-spin relaxation time T2Q in NQR is usually independent of temperature; however, it varies with temperature, in case that the EFG fluctuation at the resonant nucleus is so intense that TIQ becomes short enough to affect TZQ [2,3]. In this case, the non-adiabatic term is responsible for the TzQ variation. We have recently observed a marked temperature variation of the 35Cl NQR TzQ in Mg(H,O), SnCI,[4], which was ascribed to the local magnetic fields at the chlorine nuclei produced by the neighbouring protons being averaged by thermal motions of the [Mg(H,0)J2+ cations as a whole. In this case, the adiabatic term varies with temperature, and is responsible for the TzQ variation.') 1 Senbaru, Nishihara, Okinawa 903-01, Japan.
0.5In the present investigation, we have measured the temperature dependence of the 35Cl NQR TZQ in the deuterated Mg(D20),SnC1, and the paramagnetic Ni(H,O),SnCl, crystals in order to confirm the conclusion that T2Q of Mg(H,O),SnCl, is determined by the magnetic interaction and to investigate the NQR spin-spin relaxation mechanism in paramagnetic insulators, respectively. From now on, we will abbreviate Mg(H,O),SnCl,, Mg(D,O),SnCl,, and Ni(H,O),SnCl, as MgH, MgD, and NiH, respectively.
Experimental DetailsMgD was prepared by recrystallizing MgH from D,O (99.9%) three times. MgH (NiH) was made by dissolving SnCl, and MgCl, . 6 H,O (NiC1, ' 6 H 2 0 ) in a 6N hydrochloric acid solution with a stoichiometric ratio, and then by slow evaporation of water from the solution in a desiccator over P,O, and NaOH. MgH and NiH were not recrystallized. The polycrystalline samples obtained were sealed in glass tubes and annealed at 400...
