Magnetic susceptibility of MnCl2- and CoCl2-graphite intercalation compounds

The dc magnetic susceptibilities of MnCl2-graphite intercalation compounds (GIC GICs (stages 1, 2, and 3) were measured between 2 and 300 K for external field orientations both perpendicular and parallel to the c axis. MnCl2-GIC obeys a Curie-Weiss law for both orientations above 20 K, with g factors close to the spin-only value of 2.0 for both stages. The measured Curie-Weiss temperatures indicate a net antiferromagnetic intraplanar exchange interaction, with a small XY anisotropy appearing below about 50 K. CoCl2-GIC, in contrast, exhibits considerable XY anisotropy at all temperatures. The susceptibility perpendicular to the C axis has been fit to a Curie-Weiss law above 120 K, yielding a stage-dependent ferromagnetic intraplanar exchange (J=10.4, 7.7, and 6.8 K for stages 1, 2, and 3, respectively). The susceptibility parallel to the c axis contains a very large temperature-independent term which can be attributed to Van Vleck paramagnetism.