Approach to equilibrium of a spin-glass (original) (raw)

The decay of the thermoremanent magnetization (TRM) in the metallic spin-glass 2.6 at. /o Ag:Mn lessens its dependence on the waiting time as H and T approach the de Almeida-Thouless (AT) line. A waiting-time dependence for the decay of the TRM of the insulating spin-glass Euo 4Sro 6S is only observed at T &0.87T~. Decay of the TRM is described for both by a stretched exponential. These results suggest that equilibrium is being approached in the field-cooled state as one approaches the AT line. The issue of the approach to equilibrium in a spin-glass has been a subject of controversy. Two mutually inconsistent theoretical pictures have emerged: the dynamics' of an ultrametric distribution of pure states [e.g., the dynamics of the states associated with the Sherrington-Kirkpatrick model, or the closely associated generalized random-energy model (GREM)]; or the dynamics of a droplet model modeled on the random field Ising model. The experimental situation has also been clouded. The observation of a "stretched exponential" time dependence for the time decay of the thermoremanent magnetization (TRM) has been argued to be correct for measurement times less than the waiting time, giving rise to a