Magnetic properties of CoCl2-graphite intercalation compounds under pressure

We report ac magnetic susceptibility (χ=χ’-iχ’’) measurements of stage-1 and stage-2 CoCl2-graphite intercalation compounds (GIC’s) carried out under hydrostatic pressures of 0–15 kbar. For stage-1 CoCl2-GIC’s, it is found that the three-dimensional ordering temperature Tc2=TN=9.7 K, where the ferromagnetic planes of Co2+ spins become ordered into an antiferromagnetic arrangement along the c axis, shifts to a higher temperature with increasing pressure. Additionally, the transition field Ht, measured when a magnetic field is applied in the x-y plane, shifts to a higher field value with increasing pressure. From the increase of the transition field, we can estimate the pressure dependence of the antiferromagnetic interlayer coupling J’. For stage-2 CoCl2-GIC’s, it is found from measurements of χ’ and χ’’ that the transition temperatures Tcl and Tcu increase with applied pressure