2ND MAGNETIZATION PEAK AT LOW FIELDS DUE TO THERMOMAGNETIC FLUX-JUMP INSTABILITY

Magnetization measurements performed on a Nb thin film have revealed t he existence of a ''second magnetization peak'' (SMP) well below the u pper critical field boundary H-c2(T). The results of this work provide clear evidence that the SMP originates from a thermomagnetic flux-jum p instability. The similarity of the magnetization loops measured in B i2Sr2CaCu2O8 high-T-c superconducting crystals to those in Nb, as well as their dependence on the crystal size and field step indicate that a common mechanism is responsible for the SMP in these superconductors .