Strong Reduction of T$_{c }$Suppression by Magnetic Field in YBa$_{2}$Cu$_{3}$O$_{7+x}$ Films with Dispersed Nanoparticles

Improvements in the critical current density $J_{c}$ in applied magnetic fields are of great importance for applications of the YBa$_{2}$Cu$_{3}$O$_{7-x}$ coated conductors. Nanosize inclusions have shown to be effective in increasing $J_{c}$, but the precise physical mechanisms of their action remains elusive. A broader range of experiments is needed in order to elucidate the physics of this phenomenon. Here we discuss the magnetic field H- and temperature T-dependence of the resistivity of thin films in the normal state and near T$_{c}$. Pure YBCO films will be compared with those that contain either dispersed Y$_{2}$O$_{3 }$nanoparticles or BaSnO$_{3}$ nanorods. The resistance of highly c-axis oriented YBCO films was measured by the Montgomery method in the range 20 K $<$ T $<$ 300 K and in fields up to 9 T. The films with inclusions show a much sharper and less broadened in-field transition (smaller T$_{c}$ suppression by field) than pure YBCO. This correlates well with increased $J_{c}$ measured by conventional methods and indicates increased pinning strength at all temperatures. In order to further identify the signatures of the nano-inclusions, the samples were annealed in air at 420 deg C. The changes induced by the annealing will be discussed. \textit{This work was partially supported by AFOSR and the AFRL Propulsion Directorate. }