Interface reaction and thickness-dependent spin-diffusion effect in YBa₂Cu3O_7-δ/La_0.7Sr_0.3MnO₃ Bilayers

We have prepared a YBa₂Cu₃O₇-δ(YBCO) single layer and a YBCO/La_0.7Sr_0.3MnO₃(LSMO) bilayer with 60-nm-thick LSMO and various thicknesses of YBCO from 4.5 nm to 55 nm. The YBCO layers in both types of samples were deposited in one batch, and the superconducting properties of the YBCO/LSMO bilayer were compared with those of the YBCO single layer in order to separate the effect of interface coupling between YBCO and LSMO from other extrinsic effects. XRD data suggested that a small amount of an impurity phase in the YBCO/LSMO bilayer may be a result of an interface reaction that affects the oxygen content δ. Compared with the YBCO single layer, the critical temperature TC of the YBCO/LSMO bilayer displayed a more distinctive variation with the YBCO thickness, particularly, at thickness below 10 nm. The TC suppression with decreasing YBCO thickness could be explained by spin diffusion from the LSMO to the YBCO rather than by the proximity effect. Finally, the thicker the YBCO layer is, the larger the magnetic hysteresis loss of the YBCO/LSMO bilayer is.