Irreversibility line in Nb/CuMn multilayers with a regular array of antidots

The transport properties of superconducting multilayers with a regular array of antidots obtained by electron-beam lithography have been measured at different temperatures in the presence of external perpendicular magnetic fields. Hysteresis in the I-V characteristics was observed, which disappears when approaching the upper critical magnetic field curve H-c2(T). By comparing these data with other results (Arrhenius plots of resistive transition curves, log V-log I characteristics) we have been able to relate the onset of the hysteresis to the presence of an irreversibility line. We discuss several possible mechanisms to clarify the nature of this Line. Among them the most plausible seems to be Vortex melting mainly induced by quantum fluctuations.