Magnetic properties of stage-2 random-mixture graphite intercalation compounds and their bulk intercalants

The magnetic properties of stage-2 CocM1−cCl2 graphite intercalation compounds (GICs) (M = Ni and Mn, 0 ≤ c ≤ 1) and their bulk intercalants, CocM1−cCl2, have been studied by using d.c. magnetic susceptibility. In stage-2 CocM1−cCl2 GIC, the adjacent CocM1−cCl2 layers are separated by two graphite layers. Due to the graphite host effect, demonstrated by decreasing the antiferromagnetic interplanar exchange interaction and island formation in the intercalate layer, the magnetic phase transition of stage-2 CocM1−cCl2 GIC is very different from that of CocM1−cCl2. Stage-2 CocNi1−cCl2 GIC with 0 ≤ c ≤ 1 and stage-2 CocMn1−cCl2 GIC with 0.45 ≤ c ≤ 1 undergo a two-dimensional ferromagnetic phase transition at the critical temperature Tc, while their bulk intercalants undergo a three-dimensional antiferromagnetic phase transition at the Néel temperature TN. The magnetic properties of stage-2 GICs are compared with those of their respective bulk intercalants in the light of the graphite host effect. The magnetic properties of stage-2 CocMn1−cCl2 GIC and CocMn1−cCl2 are also compared with those of stage-2 CocMg1−cCl2 GIC and CocMg1−cCl2.