Defects in YBa2Cu3O7−δ thin films studied by magneto-optics

Koblischka, Michael Rudolf

doi:10.1016/0921-4534(96)00048-2

Cited by 6 publications

(4 citation statements)

References 15 publications

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“…The shape of the d + -lines is elliptical instead of parabolic which is, however, a purely geometric effect. Some more magneto-optical visualizations of macroscopic defects are reported in , Koblischka (1996) and Jooss et al (1998b) for scratches and notches in YBCO thin films and by Kuhn et al (1999a) for defects in large-area YBCO thin films.…”

Section: Convex Corners Crooked Edges and Holesmentioning

confidence: 91%

Magneto-optical studies of current distributions in high-T_csuperconductors

et al. 2002

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In the past few years magneto-optical flux imaging (MOI) has come to take an increasing role in the investigation and understanding of critical current densities in high-T c superconductors (HTS). This has been related to the significant progress in quantitative high-resolution magnetooptical imaging of flux distributions together with the model-independent determination of the corresponding current distributions. We review in this article the magneto-optical imaging technique and experiments on thin films, single crystals, polycrystalline bulk ceramics, tapes and melt-textured HTS materials and analyse systematically the properties determining the spatial distribution and the magnitude of the supercurrents. First of all, the current distribution is determined by the sample geometry. Due to the boundary conditions at the sample borders, the current distribution in samples of arbitrary shape splits up into domains of nearly uniform parallel current flow which are separated by current domain boundaries, where the current streamlines are sharply bent. Qualitatively, the current pattern is described by the Bean model; however, changes due to a spatially dependent electric field distribution which is induced by flux creep or flux flow have to be taken into account. For small magnetic fields, the Meissner phase coexists with pinned vortex phases and the geometry-dependent Meissner screening currents contribute to the observed current patterns. The influence of additional factors on the current domain patterns are systematically analysed: local magnetic field dependence of j c (B), current anisotropy, inhomogeneities and local transport properties of grain boundaries. We then continue to an overview of the current distribution and current-limiting factors of materials, relevant to technical applications like melt-textured samples, coated conductors and tapes. Finally, a selection of magneto-optical experiments which give direct insight into vortex pinning and depinning mechanisms are reviewed.

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Section: Convex Corners Crooked Edges and Holesmentioning

confidence: 91%

Magneto-optical studies of current distributions in high-T_csuperconductors

et al. 2002

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“…A flux penetration into isolated defects in samples after zero field cooling was reported recently. 16,19,20 As a result of the various defects present in the superconducting film, a complicated network of d ϩ lines 28,29 can be determined. These d ϩ lines are caused by a strong bending of the current paths.…”

Section: Resultsmentioning

confidence: 99%

“…18,19 One limiting factor depending on the size of the investigated areas so far was the application of a homogeneous magnetic field. Thus, the investigated superconducting thin films typically have dimensions р1ϫ1 cm 2 .…”

Section: Introductionmentioning

confidence: 99%

Large area magneto-optical investigations of YBCO thin films

Kuhn

Schey

Biegel

et al. 1999

Review of Scientific Instruments

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A new apparatus for magneto-optical investigations of high temperature superconducting ͑HTS͒ films as large as 20ϫ20 cm 2 is presented. With this equipment flux penetration of an external magnetic field into YBCO thin films has been studied by scanning the samples through an inhomogeneous magnetic field ͑magneto-optical scanning technique, MOST͒. The normal penetration of magnetic flux into a superconductor will be changed drastically in the presence of defects. The apparatus was constructed to realize an effective quality control of large area HTS thin films used for device fabrication. With this technique, a visualization of flux pattern in superconducting films larger than 1ϫ1 cm 2 is presented for the first time. The results are compared to inductive j c measurements as well as to micrographs ͓optical microscope ͑OM͒, scanning electron microscopy ͑SEM͔͒ and show that also in the large area characterization the magneto-optical method is very sensitive to microstructural defects impairing the critical current density, which is the relevant parameter for an application of the superconducting thin films. Moreover, it could be shown that MOST has appreciable advantages compared to inductive j c scans and microscopy ͑OM, SEM͒. In particular it is possible to observe defects, which are below the optical resolution of the MOST setup.

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“…netic flux penetration into a superconductor is possible by using an indicator layer showing the Faraday effect [4]- [6]. The magneto-optic allows one to study the homogeneity of superconductors on the complete sample area with a high lateral resolution and is very sensitive to the influence of defects on the current distribution [7]. According to the literature up to now magneto-optical microscopy was limited to sample areas of about 1 cm x 1 cm.…”

Section: Introductionmentioning

confidence: 99%

Defect visualization in large area YBCO thin films by magneto-optical scanning technique

Kuhn

Schey

Biegel

et al. 1999

IEEE Trans. Appl. Supercond.

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Abstract-Flux penetration in large area YBCO thin films has been studied by a magneto-optical scanning technique. With a new apparatus HTS films as large as 20 cm x 20 cm can be investigated by scanning the films through an inhomogeneous magnetic field. The apparatus has been built to realize an effective homogeneity control of the electrical properties of large area HTS thin films used for device fabrication. Magnetic flux penetration into YBCO thin films of different sizes and with intrinsic defects as well as artificial ones have been studied at 50 K. Magneto-optical measurements are compared with optical microscopy (OM) and inductive j,-characterizations. A correlation between the kind of defect and its influence on the electrical properties has been studied with regard to device applications. YBCO films structured especially for high current applications were investigated magneto-optically. These results will be compared to optical photographs of the quenching process caused by currents I > I,.

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Defects in YBa2Cu3O7−δ thin films studied by magneto-optics

Cited by 6 publications

References 15 publications

Magneto-optical studies of current distributions in high-T_csuperconductors

Magneto-optical studies of current distributions in high-T_csuperconductors

Large area magneto-optical investigations of YBCO thin films

Defect visualization in large area YBCO thin films by magneto-optical scanning technique

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Defects in YBa2Cu3O7−δ thin films studied by magneto-optics

Cited by 6 publications

References 15 publications

Magneto-optical studies of current distributions in high-Tcsuperconductors

Magneto-optical studies of current distributions in high-Tcsuperconductors

Large area magneto-optical investigations of YBCO thin films

Defect visualization in large area YBCO thin films by magneto-optical scanning technique

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Magneto-optical studies of current distributions in high-T_csuperconductors

Magneto-optical studies of current distributions in high-T_csuperconductors