Reversibility and irreversibility in spin-glasses: The free-energy surface

The free-energy surface of a mean-field model for a spin-glass in a field H is studied numerically. Field-cooled (FC) and zero-FC magnetizations are obtained that look qualitatively like experiment. The FC state is shown to satisfy Maxwell's relations. Changing H below Tg generally leads to irreversible behavior. In the absence of relaxation effects, it is found that all processes obtained upon cooling are reversible. New hysteresis effects are predicted. © 1982 The American Physical Society.