Strong flux pinning due to dislocations associated with stacking faults in Y Ba₂Cu₃O_{7 − δ}thin films prepared by fluorine-free metal organic deposition

Abstract

The magnetic-field angle dependence of the critical current density Jc(H, θ) was measured in Y Ba2Cu3O7 − δ (YBCO) thin films with strong flux pinning (Jc ≥ 2.5 MA cm − 2 at 77.3 K) prepared by a fluorine-free (FF) metal organic deposition (MOD) method and by thermal co-evaporation. Steep Jc(θ) peaks around were observed in FF-MOD films, and anisotropic scaling analysis showed that the pinning is mainly due to small random (point) pins and ab-plane-correlated pins. Few small precipitates with diameter less than 10 nm were observed by transmission electron microscopy (TEM); instead, a high density of stacking faults parallel to the ab-plane was observed in some areas in cross-sectional TEM images. We hypothesize that at 77 K most stacking faults are weak planar pinning centers by themselves and that (partial) dislocations formed at the boundary between stacking faults and the YBCO matrix become strong linear pinning centers parallel to the ab-plane. The linear pin acts as an ab-plane-correlated pin when it is perpendicular to the current direction, and acts as a small random pin in other cases, which well explains the observed Jc(H, θ) of FF-MOD YBCO films.