Ageing phenomena in a spin-glass : effect of temperature changes below Tg

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Abstract
The magnetic properties of a spin-glass depend on the time spent in the low-temperature phase : this is the so-called ageing phenomenon. We present measurements of the low-frequency a.c. susceptibility (0.01 to 0.1 Hz) and of the relaxation of the thermo-remanent magnetization in the CdCr1.7 In0.3S4 insulating spin-glass ; we investigate the influence of temperature variations on the ageing processes in the spin-glass phase, in order to get a better insight into their mechanism. The wide spectrum of relaxation times observed in spin-glass dynamics reflects the existence of many energy valleys in the phase space ; a hierarchical organization of these valleys, whose bifurcations appear as the temperature is decreased, is the simplest picture which accounts for our results