Modelling the magnetic field and temperature dependence of critical currents in high- ceramics by force induced fluxon motion

The magnetic field and temperature dependences of critical current densities in ceramic high- superconductors are described using the model of force induced fluxon motion. Fluxons start moving when the local Lorentz force exceeds the local pinning force , j(r) and B(r) are the local current density and the local magnetic induction. The model describes the change of curvature on plots of critical current against temperature at various applied magnetic fields. Results of the calculation are in good qualitative agreement with experiments. Using the same model the irreversibility line separating regions of pinned and depinned vortices in the temperature - magnetic field diagram for transport currents is derived.