Dramatic role of critical current anisotropy on flux avalanches in MgB2 films

Albrecht, J.; Matveev, A. T.; Strempfer, J.; Habermeier, H. -U.; Shantsev, D. V.; Galperin, Y. M.; Johansen, T. H.

Dramatic role of critical current anisotropy on flux avalanches in MgB2 films

Authors

Description

Anisotropic penetration of magnetic flux in MgB2 films grown on vicinal sapphire substrates is investigated using magneto-optical imaging. Regular penetration above 10 K proceeds more easily along the substrate surface steps, anisotropy of the critical current being 6%. At lower temperatures the penetration occurs via abrupt dendritic avalanches that preferentially propagate {\em perpendicular} to the surface steps. This inverse anisotropy in the penetration pattern becomes dramatic very close to 10 K where all flux avalanches propagate in the strongest-pinning direction. The observed behavior is fully explained using a thermomagnetic model of the dendritic instability.
4 pages, 5 figures