Magnetic-susceptibility studies of graphite intercalation compounds

Studies of the temperature (T) and magnetic field (H) dependence of the magnetic susceptibility (\ensuremath{\chi}) for the nonmagnetic donor graphite intercalation compounds (GIC's, K-GIC's and ${\mathrm{KH}}_{\mathrm{x}}$-GIC's) are focused on three effects. First, an anomalous temperature dependence observed at low temperature and high magnetic field is attributed to inter-Landau-level transitions near the Fermi energy (${E}_{F}$). Since the Landau-level separation of these quasi-two-dimensional electronic systems is energy dependent, we relate the Fermi energies to the temperature ${T}_{s}$, where ${k}_{B}$${T}_{s}$\ensuremath{\simeq}${\ensuremath{\Delta}}_{B}$(${E}_{F}$,H), and ${\ensuremath{\Delta}}_{B}$ is the Landau-level separation, which is dependent on both the energy and the external magnetic field. Second, in the low-magnetic-field limit where the Landau-level separation can be neglected, the stronger enhancement of the paramagnetism for higher-stage-donor GIC's with decreasing temperature is attributed to the c-axis charge inhomogeneity. The screening effect on the interior graphite layers is estimated from the temperature dependence of the susceptibility. Third, we compare the room-temperature magnetic-susceptibility values of K-GIC's and ${\mathrm{KH}}_{\mathrm{x}}$-GIC's considering both the Fermi energy and the c-axis charge distribution. The enhanced Pauli spin susceptibility of these GIC's, due to Fermi-liquid-theory effects, is shown to be significant.