Effects of nanoscale defects on critical current density of (Y 1−xEu x)Ba 2Cu 3O 7−δ thin films

Abstract

In pulsed laser deposition of YBa 2Cu 3O 7− δ films, defect introduction into the films tends to anisotropically improve the pinning along the H|| c direction due to the columnar growth mode of the process. In Eu-substituted samples, however, even though an increase in critical current density ( J c ) in the H|| c direction was observed for low fields ( H = 0.2 T), the improvement was more notable for the H|| ab-plane at both low and higher fields. Herein we present detailed TEM microstructural studies to understand these new trends in J c ( H), which are markedly different than flux pinning increases achieved with other methods, for example, with nanoparticle additions. Threading dislocations, observed in the Eu-substituted samples along the c-axis, account for J c enhancement with H|| c at low field. The enhanced ab-planar pinning in the Eu-substituted samples is attributed to the extensive bending of the {0 0 1} lattice planes throughout the film, and the crystal lattice defects with excess Cu–O planes, that were effective in increasing the J c for H|| ab at both low and high fields.