Effect of random disorder and spin frustration on the reentrant spin-glass and ferromagnetic phases in the stage-2 Cu0.93 Co0.07 Cl2 graphite intercalation compound near the multicritical point

The stage-2 Cu0.93 Co0.07 Cl2 graphite intercalation compound magnetically behaves like a reentrant ferromagnet near the multicritical point (cMCP ≈0.96). It undergoes two magnetic phase transitions at TRSG (=6.64±0.05 K) and Tc (=8.62±0.05 K). The static and dynamic nature of the ferromagnetic and reentrant spin-glass phase has been studied using dc and ac magnetic susceptibility. Characteristic memory phenomena of the dc susceptibility are observed at TRSG and Tc. The nonlinear ac susceptibility χ3′ has a positive local maximum at TRSG, and a negative local minimum at Tc. The relaxation time τ between TRSG and Tc shows a critical slowing down: τ with x=13.1±0.4 and τ0* = (2.5±0.5) × 10-13 s. The influence of the random disorder on the critical behavior above Tc is clearly observed: α=-0.66, β=0.63, and γ=1.40. The exponent of α is far from that of the three-dimensional Heisenberg model.