Critical temperature and order parameter in superconducting heterostructures with allowance for a nonzero coupling constant in a polydomain ferromagnet

The superconducting state in heterostructures containing layers of a superconductor and a ferromagnet, which is split into domains, has been studied taking into account the long-range electron–electron interaction in the ferromagnetic layer. The critical temperature and spatial distribution of the order parameter in different heterostructures have been calculated. Various types of spin valves have been examined, including a valve based on solitary reentrant superconductivity in asymmetric superconductor/superconductor/superconductor systems. A shift of the minimum has been observed in the dependence of the critical temperature of the superconductor/superconductor/superconductor system on the thickness of the ferromagnetic layer due to the presence of a domain structure. A state with alternating signs of the phase of the superconducting order parameter in one of the superconducting layers against the background of domain walls has been obtained. In superconductor/superconductor/superconductor systems, the alternation of the phase sign is also possible at the edge of one of the ferromagnetic layers because of the alternation of the magnetization direction. The possibility of using the sensitivity of the order parameter phase to magnetic inhomogeneities to create a controllable $0-\pi$ Josephson junction is discussed.