Two-Dimensional Spin Correlations in High Stage CoCl₂-Graphite Intercalation Compounds

Abstract

We present direct evidence for the two-dimensional magnetic ordering in high stage (2nd and 3rd) compounds of CoCl₂-graphite intercalation using neutron diffraction technique. Experiments from the high stage compounds show interesting features that at the lower transition temperature (T_c1) the systems undergo a three-dimensional antiferromagnetic transition but above T_c1 the scattering is characteristic of the full two-dimensional magnetic correlations. This suggests that the intermediate phase between two successive phase transitions at T_c1 and T_cu, which had been observed in the high stage CoCl₂-graphite intercalation compounds by earlier magnetic measurements, is a two-dimensional one possibly with a XY character.