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

Abstract

The origin of the magnetic flux noise in MgB2 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 (Hl) 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 Hu is strongly depends on sample geometry and temperature. This is consistent with the phenomenological model mentioned above. ©2008 The Physical Society of Japan.