Dynamics across the transition line in the insulating spin-glass Eu(0.4)Sr(0.6)S

Abstract

The thermoremanent magnetization of the insulating spin-glass Eu(0.4)Sr(0.6)S has been studied in the range 1.01 T_c down to 0.88 T_c for various initial fields, over 3 decades of time (0.30 – 300 s) by means of Faraday rotation. Within our accuracy, the decay of the TRM is well characterized by a stretched exponential law

$$\sigma = \sigma _{\rm O} \exp \{ - (t/\tau )^{1 - n} \}$$

We have studied the variation of the parameters n and τ as a function of the temperature and field. Besides the well known acceleration of the decay with increasing initially applied fields, our results in the weakest field H = 0.2 Oe exhibit a clear-cut anomaly right at the temperature T_c(H) where the transition is expected to occur in the field H = 0.2 Oe, as determined from our previous dynamical measurements. It suggests a characteristic field scale for a spin-glass which defines the field range over which linear response theory may be applicable.