Phase transitions of a nearest-neighbor Ising-model spin glass

Monte Carlo calculations exhibit a critical point in square S=1/2 Ising lattices with random nearest-neighbor interactions, which are distributed according to a Gaussian with mean zero and width ΔJ at ΔJkBTc1.0. The susceptibility χ has a cusp there, while the specific heat C has a broad peak with a maximum at somewhat higher temperatures. In nonzero external fields H the cusp of the susceptibility is rounded off, in qualitative agreement with experimental observations. Below Tc, hysteresis is found, but the remanent magnetization decays to zero very slowly. Similar nonexponential decay with time is also found for the autocorrelation function 〈σᵢ(0)σᵢ(t)〉. Some qualitative information on the occurrence of correlated spin clusters and their kinetics is also given.