heterostructures probed by polarized neutron reflectometry*

The interplay of ferromagnetism and superconductivity at interfaces can lead to proximity effects, spin valve behavior, and spin triplet pairing, with the interface playing an important role. To further explore this role, we have studied magnetotransport in YBa₂Cu₃O_7-δ (YBCO)/La_0.67Sr_0.33MnO₃ (LSMO) heterostructures fabricated via pulsed laser deposition on (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (LSAT) (001) substrates. We compare the electronic and magnetic properties of LSMO/YBCO/LSMO trilayers with YBCO/LSMO and LSMO/YBCO bilayers to separate contributions from each interface from spin valve behavior in the magnetoresistance of the samples. All samples show magnetoresistance peaks at low field, indicating the peak is due to stray fields from the LSMO layers rather than spin valve behavior. Polarized neutron reflectometry highlights the importance of the interface. All samples show a 2-3 nm thick disordered layer at each LSMO/YBCO interface, which may prevent the LSMO layers from coupling through the YBCO layer in the trilayer heterostructures and inhibit large magnetoresistance due to spin valve behavior.