Strong flux pinning due to dislocations associated with stacking faults inY Ba2Cu3O7 − δ thin films prepared by fluorine-free metal organic deposition

Abstract

The magnetic-field angle dependence of the critical current densityJc(H, θ) wasmeasured 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 analysisshowed that the pinning is mainly due to small random (point) pins andab-plane-correlated pins. Few small precipitates with diameter less than 10 nm were observed bytransmission electron microscopy (TEM); instead, a high density of stacking faults parallel to theab-plane was observed in some areas in cross-sectional TEM images. We hypothesizethat at 77 K most stacking faults are weak planar pinning centers by themselvesand that (partial) dislocations formed at the boundary between stacking faultsand the YBCO matrix become strong linear pinning centers parallel to theab-plane. The linearpin acts as an ab-plane-correlated pin when it is perpendicular to the current direction, andacts as a small random pin in other cases, which well explains the observedJc(H, θ) of FF-MOD YBCO films.