Magnetic properties of random-mixture graphite intercalation compounds

The magnetic properties of a quasi-two-dimensional mixed ferromagnetic and antiferromagnetic system, stage-2 Co_cMn_1-cCl₂ -graphite intercalation compounds (GICs), have been studied by dc magnetic susceptibility measurements. The Curie-Weiss temperature determined as a function of Co concentration indicates that the intraplanar exchange interaction between Co²⁺ and Mn²⁺ is ferromagnetic and that J(Co-Mn)=1.3 [J(Co-Co)∥J(Mn-Mn)∥]^1/2. With decreasing Co concentration c, the transition temperature tends to decrease to zero as c approaches 0.5 (the percolation concentration for the triangular lattice sites), but is not reduced to zero even below c=0.5. There may be a possibility of a spin-glass phase for 0≤c<0.4 arising from the competition between J(Mn-Mn), J(Co-Mn), and J(Mn-Mn).