Behavior of the second magnetization peak in self-nanostructured La2–xSrxCuO4 single crystals

Abstract

The occurrence of a second magnetization peak (SMP) on the dc magnetic hysteresis curves of superconducting single crystals with randomly distributed vortex pinning centers is quite common. However, the origin of this effect is still under debate. The investigation of the SMP in “self-nanostructured” (striped) La2xSrxCuO4 single crystals can offer useful information about its nature. Optimally doped and overdoped specimens (x ≥ 0.15) exhibit an SMP in a large temperature interval. By decreasing x, with the external magnetic field oriented along the crystallographic c-axis, the SMP completely disappears in the doping domain of well-developed static charge and spin stripes (x ~ 1/8) and reappears for x ≤ 0.10. This behavior follows the instability of the quasi-ordered vortex solid (the Bragg vortex glass) in the presence of static stripe order (as revealed using small-angle neutron scattering experiments), which is confirmed by the determined temperature variation of the normalized vortex-creep activation energy. If the applied field is parallel to the (a, b) planes, the SMP occurs even for specimens with static stripes, accompanied by an elastic vortex creep –plastic creep crossover. The results support the scenario in which the SMP is generated by the pinning-induced disordering of the Bragg vortex glass in the dynamic conditions of dc magnetic measurements. According to this model, for a specimen without macroscopic inhomogeneities in the pinning distribution and exhibiting an SMP, no features related to an anomalous peak effect (close to the irreversibility line) or to a first-order vortex-lattice melting should appear on the dc magnetization curves or in the ac magnetic response. This leads to a simple vortex phase diagram for the investigated system.