Superconducting transition temperature in heterogeneous ferromagnet-superconductor systems

Abstract

We study the superconducting phase transition in two systems: ferromagnet-superconductor bilayer (FSB) and a thin superconducting film with a periodic array of magnetic dots (SFMD) upon it. We show that this transition is of the first order in FSB and of the second order in SFMD. The shift of the transition temperature ΔTc due to the presence of a ferromagnetic layer may be positive or negative in the FSB and is always negative in the SFMD. The dependence of ΔTc on geometrical factors and external magnetic field is found. Theory is extended to multilayers. © 2004 The American Physical Society.