Control of Superconductivity with a Single Ferromagnetic Layer in Niobium/Erbium Bilayers

Superconducting spintronics in hybrid superconductor-ferromagnet (S-F) heterostructures provides an exciting class of device. The prototypical superspintronic device is the superconducting spin valve, where the critical temperature T-c of the S layer can be controlled by the relative orientation of two (or more) F layers. Here, we show that such control is also possible in a simple S-F bilayer. Using field history to set the remanent magnetic state of a thin Er layer, we demonstrate for a Nb/Er bilayer a high level of control of both Tc and the shape of the resistive transition R(T) to zero resistance. We are able to model the origin of the remanent magnetization, treating it as an increase in the effective exchange field of the ferromagnet and link the remanent magnetization using conventional S-F theory to the suppression of Tc. We observe stepped features in the R(T), which we argue is due to a fundamental interaction of superconductivity with inhomogeneous ferromagnetism, a phenomena currently lacking theoretical description.