Dramatic role of critical current anisotropy on flux avalanches in MgB2 films.
Anisotropic penetration of magnetic flux in MgB(2) 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, the anisotropy of the critical current being 6%. At lower temperatures the penetration occurs via abrupt dendritic avalanches that preferentially propagate 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.
Albrecht
J
J
Max-Planck-Institut für Metallforschung, Heisenbergstrasse. 3, D-70569 Stuttgart, Germany.
Matveev
A T
AT
Strempfer
J
J
Habermeier
H-U
HU
Shantsev
D V
DV
Galperin
Y M
YM
Johansen
T H
TH