Magnetic properties of graphite intercalation compounds

Comprehensive measurements of the magnetic properties of ${\mathrm{FeCl}}_3$ graphite intercalation compounds are presented with an emphasis on the low-temperature region where a susceptibility maximum is observed in all stages. This maximum, which varies in size according to stage, occurs in a very narrow temperature range and is attributed to the two dimensionality of the intercalate system. It obeys the power law of a second-order phase transition with an exponent γ which has a value between 1.8 and 2.0. The maximum occurs only in the in-plane direction with no corresponding c-axis-susceptibility response. The application of an external magnetic field drastically suppresses the susceptibility maximum and shifts it to higher temperatures. Both in-plane and out-of-plane measurements are presented and the magnetic properties of stages 1–6, as well as stage 9, are compared.