A precursor mechanism triggering the second magnetization peak phenomenon in superconducting materials

The correlation in type-II superconductors between the creep rate S and the Second Magnetization Peak (SMP) phenomenon which produces an increase in J_c, as a function of the field (H), has been investigated at different temperatures by starting from the minimum in S(H) and the onset of the SMP phenomenon detected on a FeSe_0.5Te_0.5 sample. Then the analysis has been extended by considering the entire S(H) curves and comparing our results with those of many other superconducting materials reported in literature. In this way, we find evidence that the flux dynamic mechanisms behind the appearance of the SMP phenomenon in J_c(H) are activated at fields well below those where the critical current starts effectively to increase. Moreover, the found universal relation between the minimum in the S(H) and the SMP phenomenon in J_c(H) shows that both can be attributed to a sequential crossover between a less effective pinning (losing its effectiveness at low fields) to a more effective pinning (still acting at high fields), regardless of the type-II superconductor taken into consideration.