The superconducting state can be influenced by injecting spin-polarized current in a controlled manner by properly tailoring the interfacial transmittivity between a ferromagnet ($F$) and a superconductor ($S$), resulting in a large magnetoresistance of over 1100% for a $F/I/S/I/F$ multilayer system ($I$ insulator). Because of the competition between ferromagnetism and superconductivity, the superconducting transition temperature ($T_C$) in the spin-parallel configuration is shifted below that in the spin antiparallel configuration. The $T_C$ shift is attributed to ferromagnet-induced nonequilibrium spin carriers in the superconductors.

• Received 10 November 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.267001