We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized ${\mathrm{L}\mathrm{a}}_{0.7}{\mathrm{C}\mathrm{a}}_{0.3}{\mathrm{M}\mathrm{n}\mathrm{O}}_3$ and high-$T_c$ superconducting ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_7$. This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_7$ layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures.

• Received 19 April 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.057002