Flux jumping in thin films

The thermomagnetic flux-jump instability of the Bean critical state is considered, which may occur during flux penetration in thin films of type-II superconductors in a perpendicular magnetic field. We calculate the applied field B_j at which this instability occurs and its dependence on the ramp rate Ḃ_a, on the nonlinear current-voltage curve, and on the thermal resistance between the film and the substrate. As examples we consider the thermomagnetic flux-jump instability at the straight edge of a superconducting film and of the same edge containing a small indentation of semicircular shape. The presence of a small indentation drastically reduces the field or ramp rate at which the thermomagnetic instability occurs. © 1996 The American Physical Society.