Aging dynamics of ferromagnetic and reentrant spin glass phases in stage-2 Cu${}_{0.80}$C${}_{0.20}$Cl${}_2$ graphite intercalation compound

Aging dynamics of a reentrant ferromagnet stage-2 Cu${}_{0.8}$Co${}_{0.2}$Cl${}_2$ graphite intercalation compound has been studied using DC magnetic susceptibility. This compound undergoes successive transitions at the transition temperatures $T_c$ ($\approx 8.7$ K) and $T_{RSG}$ ($\approx 3.3$ K). The relaxation rate $S_{ZFC}(t)$ exhibits a characteristic peak at $t_{cr}$ below $T_c$. The peak time $t_{cr}$ as a function of temperature $T$ shows a local maximum around 5.5 K, reflecting a frustrated nature of the ferromagnetic phase. It drastically increases with decreasing temperature below $T_{RSG}$. The spin configuration imprinted at the stop and wait process at a stop temperature $T_s$ ($<T_c$) during the field-cooled aging protocol, becomes frozen on further cooling. On reheating, the memory of the aging at $T_s$ is retrieved as an anomaly of the thermoremnant magnetization at $T_s$. These results indicate the occurrence of the aging phenomena in the ferromagnetic phase ($T_{RSG}<T<T_c$) as well as in the reentrant spin glass phase ($T<T_{RSG}$).