Transitions between $\pi$- and $0$-states in superconductor – ferromagnet – superconductor junctions

Experimental and theoretical study of superconductor (S) – ferromagnet (F) – superconductor junctions showed that in certain range of parameters (e.g., the length of the ferromagnet $d_F$, the exchange field, $E_{\rm ex}$) the ground state of the SFS junction corresponds to superconducting phase difference $\pi$ or $0$. The phase diagram of a SFS junction with the respect to $\pi$ and $0$ states is investigated in this letter in $E_{\rm ex}, d_{F}, T$ space. It is shown that the phase diagram is very sensitive to the geometry of the system, in particular, to amount of disorder in the junction.