Abstract
Non-exponential slow dynamics in the `Griffiths phase' of the three-dimensional (3D) ± J Ising spin-glass model is studied by means of Monte Carlo simulation. The distribution of relaxation times averaged over samples, {\bar P}(x) with x=lnτ, is calculated from spin auto-correlation functions simulated. It is found that {\bar P}(x) consists of two branches. The cross-over value between the branches, xc, diverges as T→ Tc, Tc being the spin-glass transition temperature. Therefore τc (=exc) is regarded as the critical relaxation time associated with the onset of the spin-glass order at Tc, and the branch of {\bar P}(x) at xc is interpreted due to the ordinary critical slowing down process ({critical dynamics}). The other branch at x>xc causes the unusual slow dynamics peculiar to spin glasses. Various aspects of {\bar P}(x) of this branch examined are consistent with the following picture; compact regions with less frustrations than the system as a whole are thermally fluctuating with very small frequencies, and independently of each others ({cluster dynamics}).
