Ageing and Memory in PLZT Above the Polar Freezing Temperature

We measured the dielectric susceptibility (200 Hz-1 MHz) and elastic compliance (1-10 KHz) of PLZT 9/65/35 with different cooling/heating protocols. By stopping the cooling run at a temperature T(1), ageing was found as a decrease in both dielectric and elastic susceptibilities, with a dependence on time almost logarithmic. On further cooling, the reference curve measured during a continuous run was rejoined, a phenomenon known as rejuvenation. The processes could be repeated at several T(n) < T(1), and the susceptibilities measured on heating partially retraced the dips formed during the ageing stages at the various T(n). All these phenomena, including the memory of multiple ageing stages, are well known in magnetic spin-glasses below the freezing temperature of the magnetic fluctuations. Here we show that PLTZ 9/65/35 exhibits memory of several ageing stages also above the temperature of the maximum of the dynamic susceptibility.