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 (^c) and for Hc (^a) from 4. 2 to 300 K. We find (1) ^c is large and paramagnetic and (2) the ratio of the molar values of ^c and the Pauli contribution to the susceptibility (₏) 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 {^c}{₏} is essentially independent of which alkali metal is intercalated (at least at stage 1). The stage dependence of {^c}{₏} is in qualitative agreement with the results of a calculation of the -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.