First-order phase transitions in ferromagnet/superconductor layered structures

We study the thermodynamics of clean structures composed of superconductor (S) and ferromagnet (F) layers and consisting of one or more SFS junctions. We use fully self-consistent numerical methods to compute the condensation free energies of the possible order parameter configurations as a function of temperature T. As T varies, we find that there are phase transitions between states characterized by different junction configurations (denoted as "0" or " π " according to the phase difference of the order parameter in consecutive S layers). We show that these transitions are of first order. We calculate the associated latent heats and find them to be measurable.