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

Abstract

We have prepared thin films of Y₁Ba₂Cu₃O_7−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 J_c 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 T_c shows that J_c follows a power law of (1−t), with t being the reduced temperature. In an applied field perpendicular to the film’s surface, J_c also drops slowly, and up to 90 kOe J_c >10⁵ A/cm² for T=4.2 K. Measurements for an off‐stoichiometric film, Y₁Ba₃ Cu₂O_7−x, give lower J_c values that fall off faster in temperature than for stoichiometric compositions.