Vortex pinning in chemical solution nanostructured YBCO films

T. Puig, J. Gutierrez, A. Pomar, A. Llordes, J. Gazquez, S. Ricart, F. Sandiumenge and X. Obradors Supercond. Sci. Technol. 21, 034008 (2008) DOI:10.1088/0953-2048/21/3/034008 A methodology of general validity to study vortex pinning in YBa₂Cu₃O_7−δ (YBCO) is described. It is based on measuring the angular-dependent critical current density in a large range of temperatures and magnetic fields and it permits one to identify, separate and quantify the three basic vortex pinning contributions associated to anisotropic–strong, isotropic–strong and isotropic–weak pinning centers. The corresponding vortex pinning phase diagrams for these three contributions are built up. This methodology is applied to the recently discovered solution-derived YBCO–BaZrO₃ nanocomposites which display a maximum vortex pinning force of 78 GN m⁻³ at 65 K, being five times larger than that of NbTi at 4.2 K. These nanocomposites show an effective anisotropy tending to unity and the best superconducting properties observed so far in YBCO. We present the richness and complexity of their microstructure and the correlation with the vortex pinning properties. The application of the vortex pinning methodology and comparison with a standard solution-derived YBCO film enable us to identify the isotropic–strong defect contribution being at the origin of their unique properties.