Magnetic susceptibility of stage-2 CocNi1-cCl2 graphite intercalation compounds

dc magnetic susceptibility measurements were carried out on stage-2 CocNi1-cCl2-graphite intercalation compounds which approximate two-dimensional randomly mixed ferromagnets with XY spin symmetry. The average effective magnetic moment and the Curie-Weiss temperature are determined as a function of cobalt concentration and discussed in terms of the molecular field approximation. The results indicate that (i) the Co2+ and Ni2+ spins are randomly distributed on the triangular lattice sites inside the intercalate layer and (ii) the intraplanar interaction between Co2+ and Ni2+ is enhanced and larger than that between Co2+ and Co2+ and that between Ni2+ and Ni2+:J(Co-Ni)=1.28J(Co-Co)J(Ni-Ni).