Phase transitions in hybrid SFS structures with thin superconducting layers

Features of a phase transition between $0$ and $\pi$ states in superconductor/ferromagnet/superconductor (SFS) Josephson structures with thin superconducting layers and a ferromagnetic barrier are studied experimentally and theoretically. The dependence of the critical temperature $T_c$ of a transition of the hybrid structure to a superconducting state on the thickness of superconducting layers $d_s$ is analyzed by a local method involving measurements of the nonlinear microwave response of the system by a near-field probe. An anomalous increase in the measured temperature $T_c$ at the reduction of the thickness $d_s$ is detected and is attributed to the $0$-$\pi$ transition.