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TT: Fachverband Tiefe Temperaturen

TT 10: Poster Session: Superconductivity

TT 10.44: Poster

Monday, March 14, 2011, 14:00–18:00, P4

Vortex motion in granular MgB₂ thin films - Investigations with magneto-optical imaging — •Claudia Stahl¹, Sebastian Treiber¹, and Joachim Albrecht² — ¹Max-Planck-Institut für Metallforschung, Stuttgart, Germany — ²Hochschule Aalen, Germany

In magnesium diboride (MgB₂) thin films there are different kinds of vortex motion. Flux flow and thermally activated flux creep form the current carrying state in an external magnetic field. At lower temperatures dynamically driven flux avalanches containing areas of vanishing supercurrents occur. Flux penetration as well as the critical current density can be determined locally and quantitatively via magneto-optical imaging based on the Faraday effect.

We use this method to measure properties of MgB₂ films with different granularity. In a particular production process we achieved to create areas of varying granularity on an individual substrate. This allows a direct analysis of the consequences of granularity.

It is shown that in granular films the dendritic state as well as the regular critical state both are modified: we find a reduced critical current density j_c, which decreases rapidly with increasing temperature. Additionally magnetic avalanches are favoured in the granular area, whereas generally they are triggered by high current densities. This requires a more detailed understanding of formation and propagation of magnetic avalanches in inhomogeneous media [1].
S. Treiber and J. Albrecht, New Journal of Physics 12, 093043 (2010).