Depolarized Light Scattering of Liquid Crystals with Addition of Carbon Tetrachloride in the Isotropic Phase

Abstract

Stage-1 Cu c Co 1−c Cl 2 graphite intercalation compounds approximate quasi-twodimensional (2D) random spin systems with competing ferromagnetic and antiferromagnetic intraplanar exchange interactions. The temperature dependence of the in-plane electrical resistivity of these compounds has been measured near critical temperatures. The magnetic resistivity ζ mag consists of the long-range spin-order part ζ LS and the spin-fluctuation part ζ SF . For 0 c 0.2 the long-range spin-order part ζ LS is dominant: the temperature dependence of ζ LS is described by a smeared power law with an exponent 2β, where β is the critical exponent of staggered magnetization. For 0.3 c 0.4 the spin-fluctuation part ζ SF becomes larger than ζ LS . For 0.5 c 0.95 no appreciable magnetic resistivity is observed. For c = 1 the derivative −dζ mag /dT shows a small peak at around 67 K due to the growth of short-range spin order which is characteristic of the 2D Heisenberg antiferromagnet. The critical behaviour of the in-plane resistivity can be explained in terms of a model based on π -d exchange interactions between π-electrons in the graphite layers and magnetic spins in the intercalate layers. The πelectrons are scattered by spins of a virtual antiferromagnetic in-plane spin configuration arising from the superposition of two ferromagnetic in-plane structures with spin directions antiparallel to each other. The π-d exchange interactions of these compounds are also discussed. † Present address: and the unpaired 3p electron of Cl − . Then the π-d exchange interaction J π −M can be rewritten asin terms of J M−M , where S = 1/2 for both the Cu 2+ spin and the fictitious spin of Co 2+ . The intraplanar exchange interaction J M−M is experimentally determined as 7.75 K for the CoCl 2 GIC and −39 K for the CuCl 2 GIC, which implies that J Co −Cl > 0 and J Cu −Cl < 0. It may be reasonable to assume that J π−Cl of the CoCl 2 GIC is equal to that of the CuCl 2 GIC because the graphite layer is sandwiched between two Cl − layers. Then the ratio of J π −Co to J π −Cu is expressed by

Re-investigation of translational–orientational coupling behavior of nematogen in isotropic phase with non-nematogenic additives

“…In previous works by Shibata et al, 14,15) the R of 5CB was reduced largely by additives of about 0.1 mole fraction, but the decreases are not remarkable even with addition of 0.10 mole of CCl 4 and TPP in this work.…”

“…The frequency-dependent shear viscosity also supports the conclusion that R is not small even with the use of additives of about 0.1 mole fraction. A significant decrease in the R of the mixtures in our previous studies 14,15) might stem from the insufficient resolution of the spectra in the low-frequency region.…”

“…Although we cannot conclude which tendency is better, it can at least be said that R does not show a significant decrease in this work in contrast to those in the literature. 14,15) Since the measurement in the low-frequency region was insufficient in the VH heterodyne dynamic light scattering measurement in previous studies, 14,15) the dip in the lowfrequency region showing the magnitude of R might be poorly determined. In this study, the improvement in the VH heterodyne dynamic light scattering measurement enabled us to evaluate the low-frequency dip even with the additives used.…”

“…This dip was observed irrespective of the additive, i.e., TPP or CCl 4 . The measurement was performed down to 0.1 MHz in this work, while the frequency region was limited to a value higher than 1 MHz used in the work of Shibata et al, 14,15) which we consider is one reason why the dip of mixtures was not observed in their work.…”

“…Heterodyne dynamic light scattering 14,15) High-frequency strain-optical coefficient measurement 16) Heterodyne dynamic light scattering …”