MODELING THE MAGNETIC-FIELD AND TEMPERATURE-DEPENDENCE OF CRITICAL CURRENTS IN HIGH-T-C CERAMICS BY FORCE INDUCED FLUXON MOTION

The magnetic field and temperature dependences of critical current den sities J(c)(B, T) in ceramic high-T-c superconductors are described us ing the model of force induced fluxon motion. Fluxons start moving whe n the local Lorentz force F-L(T) = phi(0)j(r) exceeds the local pinnin g force F-p(r) = (F) over tilde(0)B(c)(2)(T)/B(r),j(r) and B(r) are th e local current density and the local magnetic induction. The model de scribes the change of curvature on plots of critical current against t emperature at various applied magnetic fields. Results of the calculat ion are in good qualitative agreement with experiments. Using the same model the irreversibility line separating regions of pinned and depin ned vortices in the temperature-magnetic field diagram for transport c urrents is derived.