Ageing dynamics of ferromagnetic and re-entrant spin glass phases in a stage-2Cu0.80Co0.20Cl2 graphite intercalation compound

Ageing dynamics of a re-entrant ferromagnet stage-2Cu0.8Co0.2Cl2 graphite intercalation compound has been studied using DC magnetization measurements. This compound undergoes successive transitions at the transition temperatures Tc (approx 8.7 K) and TRSG (approx 3.3 K). The relaxation rate SZFC(t) exhibits a characteristic peak at fcr below Tc. The peak time tcr at constant tw shows a local maximum around 5.5 K, indicating a slow dynamics arising from a frustrated nature of the ferromagnetic phase. It drastically increases with decreasing temperature below TRSG. The spin configuration imprinted at the stop and wait process at a stop temperature Ts ( < Tc) during the field-cooled ageing protocol becomes frozen on further cooling. On reheating, the memory of the ageing at Ts is retrieved as an anomaly of the thermoremnant magnetization at Ts. These results indicate the occurrence of the ageing phenomena in the ferromagnetic phase (TRSG < T < Tc) as well as in the re-entrant spin glass phase (T < TRSG).