Temperature and field dependence of the critical current densities of Y-Ba-Cu-O films

We have prepared thin films of Y1Ba2Cu3O7−x using a coevaporation technique and measured their critical current densities as a function of both temperature and field using a transport technique. For a stoichiometric composition we find that Jc at 4.2 K in zero field is 1.04×106 A/cm2 and does not drop below 105 A/cm2 until T>60 K. Fitting the data near Tc shows that Jc follows a power law of (1−t), with t being the reduced temperature. In an applied field perpendicular to the film’s surface, Jc also drops slowly, and up to 90 kOe Jc>105 A/cm2 for T=4.2 K. Measurements for an off-stoichiometric film, Y1Ba3Cu2O7−x, give lower Jc values that fall off faster in temperature than for stoichiometric compositions.