Critical current enhancement in multilayered Y₁Ba ₂Cu₃O_7-y/Y₁Ba₂(Cu _1-xNi_x)O_7-y structures

Multilayers of YBaCuO superconductors and Ni-doped YBaCuO superconductors have been grown by the laser ablation technique to study the flux pinning properties of the nonmagnetic/magnetic superconducting heterostructures. Even though Ni doping depressed the superconducting properties of the single layer films, when sandwiched between high quality YBaCuO films, the composite showed high critical temperatures. Three-layer and five-layer structures of the YBaCuO/YBaCuNiO system become superconducting around 87 K when the doped layer thickness was below 100 Å. Three-layer structures grown on ZrO ₂(100) showed critical current densities of 3×10⁶ A/cm² at 77 K, which is about three times larger than the reported results in the literature. Epitaxial layer growth between the two superconductors was indicated by x-ray diffraction measurements, which showed complete c-axis orientation with full width at half maximum of 0.45°in a (006) line scan. Behavior of the critical current up to 0.85 T and temperatures down to 66 K has been studied. Critical current densities close to 4.5×10⁶ A/cm² in 0.85 T fields perpendicular to the films have been obtained at 67 K.