Critical current density measurements of thin films of YBaCuO

Thin films of the YBaCuO superconductor have been deposited by evaporation on SrTiO/sub 3/ substrates. After a post-anneal, the films were patterned into a four-probe geometry, and critical-current density measurements were made using a transport technique. Compositions both on and off the stoichiometric Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ were studied, and measurements were made as a function of temperature and magnetic field. At 4.2 K and in ambient field, a stoichiometric film has a J/sub c/ greater than 10/sup 6/ A/cm/sup 2/ which falls off slowly out to approximately=55 K and then follows a power law dependence (1-t)/sup 3.3/, where t is the reduced temperature. The magnetic-field dependence of J/sub c/ at 4.2 K is weak, and for applied fields of 90 kOe, J/sub c/ has dropped only a factor of 10 from the ambient field. Off-stoichiometric films have lower J/sub c/'s which fall off faster and at lower temperatures.<
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