Superconductor/ferromagnet (S/F) interfaces are fertile ground for emergent phenomena that result from competing interactions and proximity effects. Beyond their fundamental interest, these phenomena can be exploited in devices to create novel functionalities. Here, we realize all-oxide junctions based on S/F/S/F/S heterostructures that combine the high-$T_{\mathrm{C}}$ S ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ and the half-metallic F ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$, in which electrical transport is measured in current-perpendicular-to-plane configuration. These junctions show a spin-valve effect: their electrical resistance switches as the relative orientation of the magnetizations of the F layers is switched from parallel to antiparallel by a magnetic field. However, their behavior is unusual: in contrast to conventional spin valves, whether the resistance increases or decreases upon switching depends on temperature. This can be understood considering the interplay between superconducting proximity effects, spin-dependent scattering, and magnetic exchange effects. These results show a path towards high-temperature superconducting spin-valve devices for advanced quantum sensing.

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• Complex oxides
• Half-metals
• High-temperature superconductors
• Strongly correlated systems
• Superconducting devices
• Resistivity measurements