Enhanced critical current density due to flux pinning from lattice defects in pulsed laser ablated Y_1-xDy_xBa₂Cu₃O_7-δthin films

Abstract

The effect of lattice defects at the unit cell level created by the stress field when two rare earths with different ionic radii are mixed at the rare earth site, on the flux pinning and critical current density in Y 1−x Dy x Ba 2 Cu 3 O 7−δ thin films prepared by the pulsed laser deposition technique, was investigated using SQUID magnetometry at different temperatures for x = 0 to 1 in steps of 0.2. From the isothermal magnetic hysteresis recorded up to 5.5 T at 5, 35 and 77 K, the critical current density, pinning force density and irreversibility fields are estimated and their variation as a function of x analysed. An inverse relation between current density and irreversibility field is observed at all the temperatures except for the film having a 20% concentration of Dy in Y which also exhibits the highest critical current density among the films investigated, suggesting this to be the optimum composition for effective flux pinning from stress field induced lattice defects.

The Influence of the Polycrystalline State and Partial Dy Substitution on the Superconducting Properties of YBCO

“…Since the lattice parameters vary only slightly in partially substituted Dy 0.6 Y 0.4 Ba 2 Cu 3 O 7--y and Dy 0.4 Y 0.6 Ba 2 Cu 3 O 7--y , the influence of the stress field should not be as significant as it is indicated in Ref. [2].…”

“…Some authors [2] are of the opinion that the partial substitution of Y 3þ with a rare-earth ion can lead to changes in the crystal lattice which, in turn, can result in the formation of a stress field causing local flux pinning at the unit cell level. The presence of a magnetic ion also gives rise to the appearance of a magnetic sublattice, with there being controversy as to what its contribution is to the formation of the magnetic properties of the HTS material.…”

Formation of stacking faults and their correlation with flux pinning and critical current density in Sm-doped YBa2Cu3OWee1, Specht2, Cantoni3 et al. 2011Phys. Rev. B

“…Additional nanoscale imperfections created by local strain fields associated with variations in ionic size between the RE and Y have been considered as a possible origin for such J c improvement. [13][14][15] However, there are no reports that clearly identify the types of defects that are dominantly formed and act as major pinning centers when the partial substitution of RE elements is realized.…”

Superconducting Thin Films Made by Chemical Solution Deposition

“…Increasing the film thickness using CSD-MOD has proved difficult [2] compared to other deposition techniques [5], [6], while introducing artificial pinning centers by doping the RE123 has been demonstrated to significantly improve the inmagnetic-field J c . Doping is typically performed either by RE [7]- [9] or Cu [10]- [12] substitution, or by adding elements, such as Zr or Y, to form non-superconducting nanopartiles [13]. Most work on increasing J c of RE123 films has been focused on RE-substitutions and doping with nanoparticles in YBa 2 Cu 3 O 7−δ (Y123) [14], [15] and GdBa 2 Cu 3 O 7−δ (Gd123) [16].…”