Temperature Dependence of the Flux Jump Upper Threshold Field in MgB2 Thin Films

The origin of the magnetic flux noise in MgB 2 thin films is believed to be a thermo-magnetic instability, where the local dissipation created by vortex motion leads to reduced pinning, and forms a positive feedback loop which can develop into a thermo-magnetic runaway. However, only the lower threshold field ( H l ) for the appearance of this noise was investigated by the magneto-optics (MO) technique due to the field limit of the MO indicator. In this paper, we report the upper threshold field, ( H u ) which is successfully obtained by different technique using a vibrating sample magnetometer while varying temperature and the field interval. After the analysis of magnetic hysteresis curves, we found that H u is strongly depends on sample geometry and temperature. This is consistent with the phenomenological model mentioned above.