Magnetic and structural properties of stage-1 NiCl2-graphite intercalation compounds

Abstract

Stage-1 NiCl2-graphite intercalation compounds (GIC's) have been prepared under conditions of high temperature and high Cl2 pressure. These compounds have a c axis repeat distance of Ic=9.36±0.05 Å, and the intercalate has a rhombohedral interplanar stacking sequence similar to pristine NiCl2. Just as with stage-1 CoCl2-GIC's, the magnetic behavior of stage-1 NiCl2-GIC's appears always to be three dimensional. We interpret the magnetic phase transition at T=22.0±0.5 K as the Néel temperature TN. At lower temperatures, the ac susceptibility shows two magnetic field-induced transitions when a magnetic field is applied in the x-y plane. At T=11.5 K, a temperature much less than TN, the transition field values are Hc1=380 Oe and Hc2=780 Oe. Compared with similar measurements in stage-2 NiCl2-GIC's and pristine NiCl2, we estimate that the ratios of the interplanar antiferromagnetic couplings Jpristine′:Jstage–1′:Jstage–2′ are 720:24:1. These new results now provide us with two families, stage-1 and stage-2 CoCl2-GIC's and NiCl2-GIC's, from which some general trends about quasi-two-dimensional systems can be inferred.