Flux pinning and magnetic relaxation in melt-processed YBa2Cu3O7−δ doped with Li

Abstract

Melt-processed samples of YBa2Cu3O7−δ (YBCO) doped with Li additions substituting at Cu(2) plane sites were used to study the effects of doping on the superconducting temperature, critical current density, irreversibility field, upper critical field, coherence length, and magnetic relaxation as a function of temperature and magnetic field. The intrinsic superconducting properties were found only slightly influenced by Li additions at some optimal concentration (0.6at.%). At this Li concentration the volume pinning force of doped material is about five times that of undoped YBCO in intermediate magnetic fields at 77K. No significant change of the maximum volume pinning force with oxygen defects after long-time oxygenation experiment (∼450h) has been observed. The normalized pinning force of the sample optimally doped with Li obeys the same scaling law as a function of magnetic field and temperature before and after additional heat treatment, indicative of a single type of pinning centers. The time dependence of the magnetization in the standard and in the Li-doped sample has been analyzed in the framework of collective pinning theory. The magnetic relaxation measurements combined with the B-T phase diagram data provide evidence of an elastic-plastic transition. The pinning parameters estimated show a considerable enhancement of the critical current density in the optimally doped sample, but only an insignificant change in the effective activation energy, pointing to a weak pinning of pointlike pinning centers, created by Li additions.

Flux pinning and magnetic relaxation in Ga-doped LiFeAs single crystals

“…In particular, nonmagnetic impurities in YBCO, e.g., small amounts of Zn 2þ or Li þ , substituting Cu within the CuO 2 planes have shown to be very effective pinning centers without significantly decreasing T c . [7][8][9][10] While the influence of small amounts of nonmagnetic impurities on the anomalous behavior of magnetization has been thoroughly investigated in cuprates, less is known about this effect in iron pnictides. The Zn doped "1111" (LaFeAsO x ) and "122" (BaFe 2 As 2 and Ba 0.5 K 0.5 Fe 2 As 2 ) compounds are currently the most intensively studied iron pnictides with nonmagnetic impurity.…”

Effect of Li2O on the microstructure, magnetic and transport properties of Tl-2223 superconductor

“…Such curvatures have also been observed in Hg-1223 sample where possible loss of Hg was held responsible for such behavior. 18 Broadening of the superconducting transition width also has the ability to influence the hole carrier concentration and structural bonding, which may cause the change in T c and normal-state resistivity.…”

“…17,14 In melt textured YBCO, Li + was found to act as effective pinning centers at optimal concentrations. 18 Though these reports provide some understanding of the effect of chemical substitutions, no clear trend in the nature of doping can be concluded. In this work, we provide a simple route to obtain polycrystalline Tl-2223 superconductors with high reproducibility and present a way to improve its superconducting properties with the addition of Li 2 O and thermal annealing.…”

A novel magnetoscan design

“…3. Details of the top-seeding melt growth process itself can be found in literature [8][9][10][11][12]. …”