Frequency dependence of aging, rejuvenation and memory in a disordered ferroelectric

We characterize in details the aging properties of the ferroelectric phase of KTa1-xNbx O-3 (KTN), where both rejuvenation and (partial) memory are observed. In particular, we carefully examine the frequency dependence of several quantities that characterize aging, rejuvenation and memory. We find a marked subaging behaviour, with an a.c. dielectric susceptiblity scaling as w roott(w) where t(w) is the waiting time. We suggest an interpretation in terms of pinned domain walls, much along the lines proposed for aging in a disordered ferromagnet, where both domain wall reconformations and overall (cumulative) domain growth are needed to rationalize the experimental findings.