Structural and magnetic properties of ${\mathrm{CuCl}}_2$ graphite intercalation compounds

Structural and magnetic properties of stage-1, stage-2, and stage-3 ${\mathrm{CuCl}}_2$ 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 ${\mathrm{Cu}}^{2+}$ 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 ${\mathrm{CuCl}}_2$ GIC’s. ESR measurements indicate that the local magnetic symmetry of ${\mathrm{Cu}}^{2+}$ 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.