Vortex avalanches in Nb thin films: Global and local magnetization measurements

We have performed superconducting quantum interference device and mu-Hall local magnetization measurements on Nb thin films of different thicknesses (120 nm less than or equal to d less than or equal to 1200 nm) and widths (95 mu m less than or equal to w less than or equal to 900 mu m) in order to characterize the effects due to thermomagnetic instabilities (TMI's) and their geometry dependence. We show that the second magnetization peak which occurs at fields H-SMP(T) H much less than H-c2(T) depends on the sample dimensions and discuss it in terms of the classical theory of TMI's. Local magnetization measurements reveal a domelike flux profile at low fields which is not due to edge barriers. The Bean-like Bur distribution is recovered at applied fields H greater than or equal to H-SMP(T). [S0163-1829(99)04138-7].