Transition temperatures of superconductor-ferromagnet superlattices

The transition temperature Tc of superconductor-ferromagnet superlattices is calculated by solving exactly the Usadel equations. Characteristic ground-state configurations are predicted with nontrivial phase difference 0<cphi≤π between neighboring superconducting layers. An unusual oscillatory dependence of Tc on the ferromagnetic-layer thickness is obtained. For short-period superlattices it is found that the transition changes from second to first order. A comparison of theoretical results with experimental data for V/Fe superlattices is given