MAGNETIC-PROPERTIES OF COCNI1-CCL2-FECL3 GRAPHITE BIINTERCALATION COMPOUNDS

CocNi1-cCl2-FeCl3 graphite bi-intercalation compounds (GBIC's) with th e stacking sequence -G-CocNi1-cCl2-G-FeCl3-G- along the c axis have be en prepared by a method of sequential intercalation. The intraplanar e xchange interaction in CocNi1-cCl2 layers is ferromagnetic, while the intraplanar exchange interaction in FeCl3 layers is antiferromagnetic. The magnetic properties of CocNi1-cCl2-FeCl3 GBIC's have been studied by using de and ac magnetic susceptibility, and low- and high-field S QUID magnetization meaurements. The CocNi1-cCl2 layer undergoes a magn etic phase transition at the critical temperature T-c which changes fr om 19.48 K at c=0 to 9.10 K at c=1. A cluster glass phase appears belo w T-c where the spin directions of ferromagnetic clusters are frozen b ecause of frustrated interisland interactions. Due to the intervening FeCl3 layer the critical behavior of CocNi1-cCl2-FeCl3 GBIC's at T-c i s three dimensional rather than two dimensional. Below T-N (approximat e to 4 K) the cluster glass phase may coexist with an antiferromagneti c long-range order occurring in the FeCl3 layers. The effect of antife rromagnetic interplanar interaction between the FeCl3 layer and the Co cNi1-cCl2 layer is clearly seen in the magnetization of CocNi1-cCl2-Fe Cl3 GBIC's. The nature of the coexisting phase is complicated by the s pin frustration effect arising from the competition between the interp lanar interaction between FeCl3 and CocNi1-cCl2 layers and the antifer romagnetic intraplanar interaction in the FeCl3 layer.