Magneto-optical study of flux penetration and critical current densities in [001] tilt YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin-film bicrystals
- Applied Superconductivity Center, University of Wisconsin, Madison, Wisconsin 53706 (United States)
Magneto-optical (MO) imaging has been used to visualize and calculate magnetic flux and current distributions at temperatures {ital T} ranging from 7 to 80 K in thin-film [001] tilt YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} bicrystals with misorientation angles 3{degree}{le}{theta}{le}10{degree}. A characteristic cusp in the flux distribution {ital B}{sub {ital z}}({ital x},{ital y}) was observed for 5{degree}{le}{theta}{le}7{degree}, which is shown to indicate that the critical current density {ital J}{sub {ital b}} across the boundary is smaller than the intragrain {ital J}{sub {ital c}}. We use the Bean model for thin-film superconductors to calculate the observed features of the {ital B}{sub {ital z}}({ital x},{ital y}) distribution and to separate both the intragrain {ital J}{sub {ital c}} and intergrain {ital J}{sub {ital b}}({theta}) independently from the MO data. The study of angular and temperature dependencies of {ital J}{sub {ital b}}({ital T},{theta}) in bicrystals with different {theta} shows that {ital J}{sub {ital b}}({theta}) strongly decreases with {theta} above {theta}{approx_equal}5{degree}. The decrease of {ital J}{sub {ital b}}({ital T},{theta}) with temperature becomes weaker as the misorientation angle {theta} is increased, so the substantial difference in {ital J}{sub {ital b}} for 5{degree} and 7{degree} boundaries at low {ital T} turns out to be less pronounced at liquid-nitrogen temperatures. In addition, the ratio {ital J}{sub {ital b}}({theta},{ital T})/{ital J}{sub {ital c}}({ital T}) for low-angle grain boundaries is shown to exhibit an anomalous increase with {ital T}, thus indicating that the grain boundaries can provide additional flux pinning. This is plausibly associated with the grain boundary dislocations that accommodate the misorientation of the grains. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 279817
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 53, Issue 13; Other Information: PBD: Apr 1996
- Country of Publication:
- United States
- Language:
- English
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