Revealing the vortex phases and second magnetization peaks in SmBCO superconductors

Abstract

Rare earth substitution in cuprate superconductors has sparked intense interest, driving progress in both fundamental research and advanced technology. In this investigation, we focus on SmBa2Cu3O7−δ (SmBCO), synthesized via the top-seeded melt growth method, with an aim to understand the corresponding vortex phases. Despite the minimal impact on transition temperature (Tc) when yttrium in YBa2Cu3O7−δ is replaced by Sm, the critical current density (Jc) remains exceptionally high under intense magnetic fields. Introducing Sm2Ba1Cu1O5 (Sm-211) phase as point defects significantly boosts the pinning potential (U) and pinning force (Fp) and enhances their stability against external magnetic fields. Contrary to other superconductors, the SmBCO sample displays a notable peak effect in the magnetic field-dependent Jc, driven by point defects introduced by the Sm-211 phase, which prompts vortex lattice softening and initiates a transition from an ordered to a disordered vortex glass phase, leading to the emergence of a second magnetization peak. Analysis suggests that the primary pinning mechanism in SmBCO involves a combination of normal point and Δκ pinning. Additionally, investigations of the vortex glass phase beneath the thermally activated flux flow regime indicate that vortices in SmBCO may freeze into a state akin to a 2D vortex glass state. This study leads to a detailed phase diagram that clarifies the evolution of vortex phases in SmBCO.