Abstract

We report measurements of the critical current density as a function of temperature and magnetic field, J c (T, H), and field broadening of resistive transitions of c-axis epitaxial YBa2Cu3O7 thin films. The films were grown in situ onto MgO (100) by on-axis unbalanced dc magnetron sputtering using a single stoichiometric target. Measurements were done on narrow microbridges patterned by conventional photolithography and wet etching. SEM and STM images of the film surface morphology show a large density of screw dislocations (2265 109 cm-2) and associated growth spirals. J c is found to increase with decreasing specimen line width suggesting enhanced pinning at the film edge. The temperature dependence (self-field conditions) of J c is fitted by flux creep theory using pinning energy U(0)=75–100 meV. The field broadening of resistivity and the field dependence of J c are highly anisotropic. V-I plots show a characteristic jump in voltage due to a sudden depinning of flux lines.

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