Cluster-glass percolative scenario in CeNi1-xCux studied by very low-temperature ac susceptibility and dc magnetization

Measurements of the ac susceptibility and dc magnetization on intermetallic alloys of CeNi1-xCux (x=0.6, 0.5, and 0.1) down to very low temperature (similar to 100 mK) are reported. The data show that a cluster-glass state is formed at a freezing temperature T-f. The dynamics of the x=0.1 alloy can be well accounted for by simple thermal activation indicating weak interactions between the clusters. On the other hand, for x=0.6 and 0.5 concentrations, the data near the freezing temperature are best fitted to a critical slowing down process characterized by the dynamic exponents z nu similar to 8 and beta similar to 0.7. The zero field cooled and field cooled magnetization curves show irreversibility above the freezing temperature which indicates the presence of an inhomogeneous dynamic magnetic state in the range T-f<T<T-ir. No anomalies related to the onset of the ferromagnetic state are detected below the freezing point in any of the alloys. A staircaselike behavior is observed in the very low temperature (T < 500 mK) hysteresis loops of the ferromagnetic alloys and is field dependent. The discreet jumps are due to the existence of mesoscopic domainlike avalanches. All these findings shed light on the dynamical nature of the cluster-percolative scenario proposed for these series.