Dendritic magnetic avalanches in carbon-free MgB2 thin films with and without a deposited Au layer

From magneto optic images (MOI), the dendritic magnetic avalanche is known to appear dominantly for thin films of the newly discovered MgB2. To clarify the origin of this phenomenon, we studied in detail the MOI of carbon-free MgB2 thin films with and without a deposited gold layer. The MOI indicated that carbon contamination was not the main source of the avalanche. The MOI clearly showed that the deposition of metallic gold on top of a MgB2 thin film improved its thermal stability and suppressed the sudden appearance of the dendritic flux avalanche. This is consistent with the previous observation of flux noise in the magnetization.