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

Surface wave velocities of crosslinked polyacrylate hydrogels were measured as a function of water content with different compositions of sodium polyacrylate (NaPA) and polyacrylic acid (PAA). The water content and composition dependencies of the surface wave velocity were discussed.