A study of the free energy surface of an Ising spin glass

We study the free energy surface of a mean field model for a spin glass in a field H. We obtain field cooled and zero field cooled magnetizations that look qualitatively like experiment. The field cooled state which has the lowest free energy of any state we generated, satisfies Maxwell's relations. All states obtained by cooling have reversible properties (in the absence of relaxation effects). By contrast, any change in H below the glass transition leads to irreversibility (minima hopping), except at very large H. We have calculated hysteresis loops which compare favorably with experiment for a variety of situations and make predictions for additional hysteretic effects.