Upper critical fields of superconductor-ferromagnet multilayers

Abstract

Nucleation of the superconducting phase in superconductor-ferromagnet multilayers is studied theoretically. When the superconducting layers are thin and decoupled by pair breaking in the ferromagnetic layers, the parallel critical field exhibits a nonlinear temperature dependence and nonmonotonic thickness dependence. The perpendicular critical field, corresponding to the nucleation of strongly modulated vortices, is also calculated. The theoretical results are in good agreement with experimental data for V/Fe multilayers.