Structural and magnetic properties of CuCl2 graphite intercalation compounds

Structural and magnetic properties of stage-1, stage-2, and stage-3 CuCl2 graphite intercalation compounds (GIC's) were studied by means of x-ray, electron- and neutron-diffraction, dc magnetic susceptibility, and electron spin resonance (ESR) measurements. The Cu2+ ions form an isosceles triangular lattice with one short side and two longer sides. The in-plane dc magnetic susceptibility shows Curie-Weiss behavior above 150 K, a broad maximum around 62-65 K, indicative of low-dimensional magnetic correlations, and a Curie-type behavior below 20 K, attributable to paramagnetic inhomogeneities in the sample. The temperature and magnitude of the susceptibility maximum are more consistent with a two-dimensional Heisenberg antiferromagnet than a one-dimensional model, suggesting that the distortion from an equilateral triangular lattice is not an important factor in the magnetic behavior of CuCl2 GIC's. ESR measurements indicate that the local magnetic symmetry of Cu2+ spins is tetragonal. The angular dependence of the ESR linewidth at 4.2 K is explained by the combined effects of a canting of the tetragonal axis from the c axis and a weak anisotropy in the Landé g factor that favors spins to lie in the intercalate plane. No magnetic phase transition is observed from dc magnetic susceptibility down to 1.5 K and magnetic neutron scattering above 0.5 K.