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

We have performed superconducting quantum interference device and {μ}-Hall local magnetization measurements on Nb thin films of different thicknesses (120nm<~d<~1200nm) and widths (95μm<~w<~900μm) 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 HSMP(T)Hc2(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 flux distribution is recovered at applied fields H>~HSMP(T).