Achieving High and Isotropic Pinning in Multilayer BaZrO 3 /YBa 2 Cu 3 O 7-x Films

In a recently developed multilayer (ML) scheme, two or more 10-nm thick Ca0.3Y0.7Ba2Cu3O7-xspacers were inserted into BaZrO3-doped YBa2Cu3O7-x(BZO/YBCO) films to enable dynamic diffusion of Ca ions from the spacers to BZO/YBCO layers. In these ML BZO/YBCO nanocomposite films, significantly enhanced pinning has been attributed to Ca/Cu substitution on the Cu-O planes of YBCO, leading to reduced lattice mismatch and hence defects at the BZO/YBCO interface. In this work, we further probe the Ca diffusion in the five-layer ML films by varying the thickness of the two Ca0.3Y0.7Ba2Cu3O7-xspacers in the range of 1 nm-10 nm and also the thickness of the three BZO/YBCO layers in the range of 50–330 nm. Ca diffusion has been found highly effective if the spacer layer thickness exceeds 2 nm and can diffuse through large BZO/YBCO thicknesses up to 330 nm (total film thickness ∼ 1 µm) along the BZO/YBCO interface. The critical current density exhibits enhanced and almost thickness-independent trends in the ML BZO/YBCO nanocomposite films. Significantly enhanced pinning is illustrated in up to 5 folds enhancement ofJcat 65 K and 9.0 T. At lower temperatures, the enhanced pinning extends to a broad range of the orientations of magnetic field (B). At 20 K and 9.0 T, theIcis up to 654 A/cm-width at B//c, which is close to 753 A/cm-width at B//ab due to the intrinsic pinning, has been achieved. This result suggests that the ML scheme provides an interesting approach to improve pinning in nanocomposite films.