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The effects of quantum fluctuations on the proton glass phase in mixed hydrogen-bonded ferro-antiferroelectric systems are considered. The system is described in terms of the infinite-ranged Ising pseudospin glass model in a transverse tunneling field in the presence of random parallel fields. The stability limit of the high-temperature proton glass phase is determined within the thermofield dynamic approach, and the behavior or linear and nonlinear susceptibility is evaluated. 相似文献
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The charge transfer compound TDAE-C60 (TDAE — tetrakis-dimethylamino-ethylene) is so far the only known C60 based molecular ferromagnet. The ESR spectra of TDAE-C60 single crystals demonstrate that freshly grown regularly shaped single crystals show at first an AFM (antiferromagnetic)-like behavior which changes upon annealing at room temperature in vacuum to a FM (ferromagnetic) one. It thus seems that annealing induces a change in the relative orientation of the distorted C 60 ? ions resulting in a change in the sign of the effective magnetic interactions between neighboring C 60 ? ions. A structural transition in the TDAE methyl protons at 250 K seems to be connected with this process. Here we review the structure, the ESR spectra, the proton NMR spectra and the13C NMR spectra of TDAE-C60. 相似文献
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Using a proton-nitrogen double resonance technique we have determined the quadrupole coupling of14N in the room temperature orthorhombic (Cmca), the low temperature tetragonal (P42/ncm), and the monoclinic low temperature (P21/c) phases of (CH3NH3)2CdCl4. In all these phases all nitrogens are chemically equivalent demonstrating that the disorder in the orientations and H-bonding arrangements of the CH3-NH3 groups in theC m c a andP42/ncm phases is indeed dynamic and not static. In the monoclinic phase the14N quadrupole coupling constant equalse
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qQ/h=880 kHz and the asymmetry parameter is=0.20, wherease
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qQ/h=790 kHz,=0.1 in the tetragonal low temperature phase ande
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qQ/h=726 kHz,=0.21 in the room temperature orthorhombic phase. The observed increase in the14N quadrupole coupling constant on going from the orthorhombic phase to the tetragonal low temperature phase which is coupled with a simultaneous decrease in the asymmetry parameter can be understood in terms of a partial freezing in of the dynamic disorder in the C-N bond directions whereas the14N quadrupole coupling tensor in the monoclinic phase is characteristic of a frozen in C-N bond in a deformed lattice, where the N-H — Cl bonds are of different length. 相似文献
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The temperature dependence of the 17O NQR spectra of the O-H---O bonded oxygens in PbHPO4 have been studied using a proton-17O double resonance technique. The results show that the protons move between two off-centre sites above Tc and freeze into one of the possible equilibrium sites below Tc. 相似文献
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I. Zupan
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G. Lahajnar R. Blinc D. H. Reneker A. Peterlin 《Journal of Polymer Science.Polymer Physics》1978,16(8):1399-1407
The diffusion coefficient of butane in linear polyethylene at room temperature as a function of the vapor pressure of butane was measured by the spin-echo method with a pulsed magnetic field gradient. For the Special morphology of randomly oriented stacks of parallel lamellas the detour factor is 1/3. As long as the blocking factor and migration through the lamellas can be neglected, the local diffusion coefficient Da of the small molecules through the amorphous layers in the direction parallel to the lamellas is three times the apparent diffusion coefficient D derived from the decay of the amplitude of the spin echo under the assumption of an infinitely extended homogeneous medium. The diffusion coefficient and the spin–spin relaxation time both increase exponentially with increasing pressure, i.e., butane concentration in the polymer, while the spin-lattice relaxation time is pressure independent and seems to be determined by interaction with the amorphous polyethylene matrix. 相似文献