Aging dip and cumulative aging in hierarchical successive transition of stage-2 CoCl${}_2$ graphite intercalation compound

Abstract

Memory and aging behaviors in stage-2 CoCl${}_2$ GIC ($T_{cu}$ = 8.9 K and $T_{cl}$ = 6.9 K) have been studied using low frequency ($f$ = 0.1 Hz) AC magnetic susceptibility (${\chi }^{\prime }$ and ${\chi }^{\prime \prime }$) as well as thermoremnant magnetization. There occurs a crossover from a cumulative aging (mainly) with a partial memory effect for the domain-growth in the intermediate state between $T_{cu}$ and $T_{cl}$ to an aging and memory in a spin glass phase below $T_{cl}$. When the system is aged at single or multiple stop and wait processes at stop temperatures $T_s$'s below $T_{cl}$ for wait times $t_s$, the AC magnetic susceptibility shows single or multiple aging dips at $T_s$'s on reheating. The depth of the aging dips is logarithmically proportional to the wait time $t_s$. Very weak aging dip between $T_{cu}$ and $T_{cl}$ indicates the existence of a partial memory effect. The sign of the difference between the reference cooling and reference heating curves changes from positive to negative on crossing $T_{cl}$ from the high $T$-side. The time dependence of ${\chi }^{\prime }$ and ${\chi }^{\prime \prime }$ below $T_{cl}$ is described by a scaling function of $\omega t$. its a local maximum at 6.5 K just below $T_{cl}$, and drastically decreases with increasing $T$. The nature of the cumulative aging between $T_{cl}$ and $T_{cu}$ is also examined.

11 pages. 13 figures, 1 table