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Lucica Miu1

1, National Institute of Materials Physics, Bucharest-Magurele, , Romania

The origin of the spectacular enhancement of the effective critical current density with increasing external magnetic field H, leading to a second magnetization peak (SMP) on the dc magnetic hysteresis curves of superconducting single crystals with random pinning, is still not clear. Many interesting SMP models and mechanisms have been proposed and considered so far, and it is believed at present that this effect is system dependent. However, by analyzing the dc magnetization relaxation in the SMP domain for various single crystal specimens (superconducting cuprates and iron-based superconductors), of different pinning strength, with H oriented along the crystallographic c axis or perpendicular to it, we found several sample independent, characteristic aspects, such as the absence of single-vortex collective pinning around the SMP onset field, and the sign changing of the vortex creep exponent between the onset field and the peak field. This general behavior and the peculiar disappearance of the SMP in certain underdoped cuprates and pnictides (attributed by us to the presence of SDW stripe-like static order) support strongly a continuous pinning-induced disordering of the low-H quasi-ordered vortex solid as the actual scenario for the SMP.

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