Comparative review of aging properties in spin glasses and other disordered materials

Aging phenomena have been studied in very different materials like polymers, supercooled liquids or disordered orientational crystals. We recall here the main features of aging in spin glasses, and use this example of magnetic systems as a guideline for the description of the others. A particular attention is put on the sensitivity of aging to the cooling rate and to temperature variations. This allows us to point out differences between temperature specific processes, yielding " rejuvenation and memory effects " as known in spin glasses, and domain growth processes, giving cumulative contributions at different temperatures. The relevance of wall depinning processes to rejuvenation and memory effects is discussed at the light of recent results on disordered ferromagnets. In materials science, aging is most commonly viewed in terms of a steady degradation of the properties of the considered material and is mostly a consequence of the action of some external factor (chemical reaction, irradiation effects, mechanical fatigue ...). However many materials and especially disordered materials experience a spontaneous long time evolution, without any external agent, whose direct consequences can be as important as for the usual chemical aging. This is well known in structural glasses and amorphous polymers and is referred to as physical aging. 1) Much work has been done on these systems, since it was first recognised that their quenched state was unstable and evolved as a function of time (the aging time 2, 3)). As quoted by L.C.E. Struik 1) " the phenomenon of physical aging is very important from a practical point of view. Several properties of glassy polymers, e.g. their small strain mechanical properties, undergo marked changes and strongly depend on the aging time. In the testing of such plastics, the aging time is just as important as other parameters such as temperature, stress level, humidity, etc. Furthermore, a knowledge of the aging behaviour of a material is indispensable to the prediction of its long-term behaviour from