Bending of magnetic avalanches in Mg B2 thin films

The penetration of magnetic flux into a superconductor above the lower critical field does not necessarily happen in a regular way. It is found that under particular conditions, a chaotic penetration in form of magnetic avalanches occurs. These avalanches are closely related to the so-called thermomagnetic instability, which identifies local heating due to flux line movement as the origin of the effect. In case of Mg B2 thin films, these avalanches are found only below T=10 K and are suppressed by a covering metallic layer with high thermal conductivity and sufficient thickness. These avalanches are observed in the case of partly gold covered Mg B2 films by the magneto-optical Faraday effect. The investigation of avalanches propagating into a gold-covered region revealed a change of the propagation direction depending on the incident angle of these avalanches.