Supercurrent in Long SFFS Junctions with Antiparallel Domain Configuration

We calculate the current-phase relation of a long Josephson junction consisting of two ferromagnetic domains with equal, but opposite magnetization $h$, sandwiched between two superconductors. In the clean limit, the current-phase relation is obtained with the help of Eilenberger equation. In general, the supercurrent oscillations are non-sinusoidal and their amplitude decays algebraically when the exchange field is increased. If the two domains have the same size, the amplitude is independent of $h$, due to an exact cancellation of the phases acquired in each ferromagnetic domain. These results change drastically in the presence of disorder. We explicitly study two cases: Fluctuations of the domain size (in the framework of the Eilenberger equation) and impurity scattering (using the Usadel equation). In both cases, the current-phase relation becomes sinusoidal and the amplitude of the supercurrent oscillations is exponentially suppressed with $h$, even if the domains are identical on average.