Weak links and critical current density in Bi₂Sr ₂CaCu₂O_x thin films

Magnetization measurements were performed on epitaxial and textured Bi ₂Sr₂CaCu₂O_x thin films deposited on (100) LaAlO₃ and MgO substrates. An anomalous dependence of the critical current density derived from magnetization hysteresis measurement on magnetic field is observed. The measured critical current density shows a minimum at a magnetic field (H_m) far below the upper critical field H_c2. The measured H_m in epitaxial films has an exponential dependence on temperature, e^-T/T₀ (T₀∼12.5 K). The anomalous field dependence of critical current density is attributed to the presence of weak links in the films.