Memory and aging effect in hierarchical spin orderings of stage-2 CoCl_{2} graphite intercalation compound

TL;DR

This study investigates the aging, memory, and rejuvenation effects in the magnetic phase transitions of stage-2 CoCl₂ graphite intercalation compound, revealing complex spin glass behavior between two critical temperatures.

Contribution

It provides experimental evidence of memory and aging effects in a layered magnetic system, linking these phenomena to the droplet model of spin glasses.

Findings

Memory of spin configurations is retained during heating after field cooling.

Magnetization exhibits characteristic memory and rejuvenation effects.

Relaxation rate shows two peaks indicating complex aging dynamics.

Abstract

Stage-2 CoCl$_{2}$ graphite intercalation compound undergoes two magnetic phase transitions at $T_{cl}$ (= 7.0 K) and $T_{cu}$ (= 8.9 K). The aging dynamics of this compound is studied near $T_{cl}$ and $T_{cu}$. The intermediate state between $T_{cl}$ and $T_{cu}$ is characterized by a spin glass phase extending over ferromagnetic islands. A genuine thermoremnant magnetization (TRM) measurement indicates that the memory of the specific spin configurations imprinted at temperatures between $T_{cl}$ and $T_{cu}$ during the field-cooled (FC) aging protocol can be recalled when the system is re-heated at a constant heating rate. The zero-field cooled (ZFC) and TRM magnetization is examined in a series of heating and reheating process. The magnetization shows both characteristic memory and rejuvenation effects. The time $(t)$ dependence of the relaxation rate $S_{ZFC}(t)=(1/H)$d$M_{ZFC}(t)$/d$\ln t$ after the ZFC aging protocol with a wait time $t_{w}$, exhibits two peaks at characteristic times $t_{cr1}$ and $t_{cr2}$ between $T_{cl}$ and $T_{cu}$. An aging process is revealed as the strong $t_{w}$ dependence of $t_{cr2}$. The observed aging and memory effect is discussed in terms of the droplet model.