Effect of Magnetic Field on Resistive Transition of Thin Film Thallium Based Superconductors

The temperature and magnetic field dependences of a.c. resistance of c-axis oriented (Tl$\text{}_{0.5}$Pb$\text{}_{0.5}$)(Sr$\text{}_{0.8}$Ba$\text{}_{0.2}$)$\text{}_{2}$Ca $\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{x}$ and (Tl$\text{}_{0.6}$Pb$\text{}_{0.24}$Bi$\text{}_{0.16}$)(Sr$\text{}_{0.9}$Ba$\text{}_{0.1}$)$\text{}_{2}$Ca$\text{}_{2}$Cu$\text{}_{3}$ O$\text{}_{x}$ thin films as well as of (Tl$\text{}_{0.5}$Pb$\text{}_{0.5}$)(Sr$\text{}_{0.8}$Ba$\text{}_{0.2}$)$\text{}_{2}$Ca$\text{}_{ }$2Cu$\text{}_{3}$O$\text{}_{x}$ bulk sample from 77 K to room temperature and in magnetic fields from zero to 3000 Oe were measured and analyzed. The magnetic field and temperature dependence of the resistive superconducting transition and irreversibility field were discussed both in the flux-creep model and in the superconducting liquid vortex state model. The temperature width of resistive transition was explained taking advantage of the Ambegaokar and Halperin model of the resistance of superconducting Josephson weak links and barrier of vortex motion presented by Tinkham. The irreversibility field was described by an exponential formula.