Improving the ratio of the grain-boundary and bulk critical currents in YBa2Cu3O7−δ film

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Magneto-optical images of flux patterns in a ring of epitaxial YBa2Cu3O7−δ film with an artificial 10° grain boundary are used to determine the ratio of the grain-boundary critical current to the bulk critical current. This ratio which first increases slowly with temperature is found to make a sharp upturn above 77 K showing that the grain-boundary critical current quickly converges to the bulk value at higher temperatures. From the measured ratio and the grain-boundary critical current obtained from magnetization, the temperature dependence of the bulk critical current is recovered.