THEORY OF MAGNETIC-SUSCEPTIBILITY OF GRAPHITE-INTERCALATION COMPOUNDS

The orbital magnetic susceptibility (χorc) of graphite intercalation compounds is calculated for H→c→ using a tight-binding model for the π-electron energy bands and the compact expression for χorc derived by Fukuyama, which includes both intraband and interband terms. The results are presented as an approximate analytic expression for χorc as a function of Fermi level μ (0<μ3 eV) and temperature. For μkBT1 the susceptibility is large and diamagnetic (due to interband transitions), while for kBTμ3 eV, χorc is paramagnetic (mainly due to intraband transitions) in contrast to the usual Landau-Peierls diamagnetism of conduction electrons in parabolic bands. Furthermore, χorc is shown to be a sensitive function of μ and hence of the conduction-electron charge distribution in each graphite layer. We show that this theory accounts for the main features of the experimental data (stage and temperature dependence of χorc) and suggest that measurements of the stage dependence of χorc can be used to estimate the c-axis screening length in graphite intercalation compounds. © 1979 The American Physical Society.