Advanced memory effects in the aging of a polymer glass

Abstract

A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant ǫ. A temporary stop of cooling produces a downward relaxation of ǫ. Two main features are observed i) when cooling is resumed ǫ goes back to the values obtained without the cooling stop ( i.e. the low temperature state is independent of the cooling history) ii) upon reheating ǫ keeps the memory of all the cooling stops(Advanced memory). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs. : 75.10.Nr, 77.22Gm, 64.70Pf, PACS

Rejuvenation and memory in model spin glasses in three and four dimensions

“…This is not totally unexpected, as we already know experimentally that systems quite different from spin glasses show memory and rejuvenation. [12][13][14][15][16] The natural conclusion is that chaos, although probably present in realistic spin glasses, 34,38,47 need not be invoked to explain memory and rejuvenation. However, it has been argued 11 that the experimental protocol introduced in Ref.…”

“…This was maybe to be expected, since memory and rejuvenation is being found experimentally in materials where chaos in temperature seems to be absent or where a thermodynamic glass transition has never been found. [12][13][14] Unfortunately, we have made no progress 39 in the analysis of the dip-experiment protocol.…”

“…Yet, upon reflection, one realizes that the experimental direct quench bears little resemblance with the simulational one. In fact, the experimental sample that is "instantaneously" quenched to 0.4T c , expends at least 10 sec ͑ϳ10 13 MCSs!͒ in the spinglass phase.…”

Superparamagnetism and Spin Glass Dynamics of Interacting Magnetic Nanoparticle Systems

“…On subsequent reheating the ac susceptibility shows a dip around each aging temperature -the system has kept a memory of each equilibration at constant temperature. The memory experiment is an efficient tool to study spin-glass-like properties in various materials [114][115][116][117][118]. For the Ag(11 at% Mn) sample, the ac susceptibility curve measured on cooling lies below the curve subsequently measured on heating, except close to the lowest temperature (see Fig.…”

Temperature cycles in the Heisenberg spin glass

“…This temperature cycling protocol has been used extensively to characterize several spin glass systems 2,3,4,5,6,7,8,9,10,11,12,13,14,15 , and these studies motivated similar cycling experiments on many different types of glassy materials 16,17,18,19,20,21,22,23,24,25 . Numerical studies of temperature shifts and cycles in the Ising version of the model have been reported 26,27,28,29,30,31,32,33 , and temperature cycles have been discussed theoretically 34,35,36,37,38,39,40,41,42 .…”