C-axis resistivity of graphite intercalation compounds

The c-axis resistivity (Formula presented) of stage-2, -3, -4, -5, and -6 (Formula presented) graphite intercalation compounds (GIC’s) has been measured in the temperature range between 4.2 and 300 K with and without an external magnetic field along the c axis. The resistivity for stage-3, -4, and -5 (Formula presented) GIC’s shows a logarithmic increase (lnT) with decreasing temperature at low temperatures. The stage-4, -5, and -6 (Formula presented) GIC’s show a negative longitudinal magnetoresistance (MR), while the stage-2 and -3 (Formula presented) GIC’s show a positive longitudinal MR. Because of high anisotropy in resistivity, the c-axis conduction is dominated by the in-plane conduction. The logarithmic behavior and negative MR in (Formula presented) are discussed in terms of the two-dimensional weak localization effect occurring in the graphite basal plane. The possibility of the Kondo effect is not ruled out because of possible exchange interactions between conduction electrons and (Formula presented) spins having an effective magnetic moment of 1.83-1.95(Formula presented). The temperature dependence of (Formula presented) varies with the stage number: metallic behavior for stage-2 and semiconductorlike behavior for stage-5 (Formula presented) GIC. The resistivity (Formula presented) of stage-3 (Formula presented) GIC has a local maximum around 267 K. These behaviors of (Formula presented) are also discussed in terms of conduction mechanisms including conduction paths, phonon- and impurity-assisted hopping, and small polaron effect.