Critical current density measurements of thin films of YBaCuO

Thin films of the YBaCuO superconductor have been deposited by evaporation on SrTiO₃ 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 Y₁Ba₂Cu₃ O_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_c greater than 10⁶ A/cm² which falls off slowly out to ≈55 K and then follows a power law dependence (1-t)^3.3, where t is the reduced temperature. The magnetic-field dependence of J_c at 4.2 K is weak, and for applied fields of 90 kOe, J_c has dropped only a factor of 10 from the ambient field. Off-stoichiometric films have lower J _c´s which fall off faster and at lower temperatures