Transport properties of stage-1 magnetic random-mixture graphite intercalation compounds

We have measured the temperature dependence of the in-plane electrical resistivity for stage-1 GICs and stage-1 GICs () in the temperature range between 2.6 and 300 K. The resistivity shows a drastic increase with decreasing temperature below the critical temperature for stage-1 GICs () and stage-1 GICs (). The temperature dependence of this resistivity anomaly is described by a smeared power law with an exponent , where is the critical exponent of the spontaneous magnetization. This anomaly is explained in terms of a model based on the - d exchange interaction between -electrons in the graphite layers and spins in the intercalate layers. Below , two-dimensional (2D) ferromagnetic intercalate layers are antiferromagnetically stacked along the c-axis. The -electrons are scattered by spin fluctuations 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 Co concentration dependence of for stage-1 GICs is also discussed in the light of the 2D percolation problem.