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

TL;DR

This study investigates how critical current anisotropy influences flux penetration and avalanche behavior in MgB2 films, revealing temperature-dependent anisotropic flux dynamics explained by a thermomagnetic model.

Contribution

It demonstrates the dramatic impact of critical current anisotropy on flux avalanches and provides a thermomagnetic explanation for the observed anisotropic flux behavior.

Findings

Flux penetration is easier along substrate steps above 10 K.

At lower temperatures, flux avalanches propagate perpendicular to surface steps.

Near 10 K, flux avalanches align with the strongest-pinning direction.

Abstract

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.