Large anisotropy and stage dependence of the magnetic susceptibility of alkali-graphite intercalation compounds

We have measured the magnetic susceptibility of alkali-graphite intercalation compounds for →H parallel to the hexagonal →c axis (χᶜ) and for →H⊥→c(χᵃ) from 4.2 to 300 K. We find (1) χᶜ is large and paramagnetic and (2) the ratio of the molar values of χᶜ and the Pauli contribution to the susceptibility (χP) as inferred from the specific heat increases rapidly as a function of stage, varying from about 2.4 in stage 1 to 17 in stage 4. The ratio χᶜχP is essentially independent of which alkali metal is intercalated (at least at stage 1). The stage dependence of χᶜχP is in qualitative agreement with the results of a calculation of the π-electron orbital contribution to the susceptibility of graphite intercalation compounds. The orbital part of the susceptibility is shown to be sensitive to the conduction-electron charge distribution from layer to layer in stage 3 and higher compunds, while the spin susceptibility and specific-heat coefficient are less sensitive to this distribution.