Spatially resolved studies of chemical composition, critical temperature, and critical current density of a YBa2Cu3O7−δ thin film

Abstract

Spatially-resolved studies of a YBa2Cu3O 7−δ thin film bridge using electron probe microanalysis (EPMA), low-temperature scanning electron microscopy (LTSEM), and magneto-optical flux visualization (MO) have been carried out. Variations in chemical composition along the bridge were measured by EPMA with 3 µm resolution. Using LTSEM the spatial distributions of the critical temperature, Tc, and of the local transition width, ∆Tc, were determined with 5 µm resolution. Distributions of magnetic flux over the bridge in an applied magnetic field have been measured at 15 and 50 K by magneto-optical technique. The critical current density jc as a function of coordinate along the bridge was extracted from the measured distributions by a new specially developed method. Significant correlations between jc, Tc, ∆Tc and cation composition have been revealed. It is shown that in low magnetic fields deviation from the stoichiometric composition leads to a decrease in both Tc and jc. The profile of jc follows the Tc-profile on large length scales and has an additional fine structure on short scales. The profile of jc along the bridge normalized to its value at any point is almost independent of temperature.

Magneto-optical studies of current distributions in high-Tcsuperconductors

“…In contrast, for continuously varying |j|, e.g. for a local field dependence of j c (B), or continuously varying transition temperatures (Gaevski et al 1998), no splitting of the current pattern into domains of different magnitudes can occur. We will consider now the case where the magnitude of the current density is sharply varying in an area, where the boundary condition for the sample requires a uniform current flow parallel to the sample edge.…”

Reason for high critical current in thin YBCO films prepared by laser ablation from nanostructured target

“…At least it is known that non-stoichiometric films prepared with molecular chemical vapour deposition (MOCVD) have a stoichiometric YBCO matrix with nonstoichiometric precipitates [3] and that Y-rich and Bapoor films have high J c [4]. However, there are also contradicting results showing that J c has a maximum near the stoichiometric 123 composition [5][6][7]. Therefore it is difficult to find a simple rule for how non-stoichiometric metallic compositions actually affect the value of J c in thin YBCO films.…”

Symmetry of the remanent-state flux distribution in superconducting thin strips: Probing the critical state

“…It may be caused, e. g., by a nonuniform chemical composition. 21 The kind of deviation shown in Fig. 4 can be explained by a suppressed j c near the strip edge.…”