Local threshold field for dendritic instability in superconducting MgB2 films

Abstract

Using magneto-optical imaging the phenomenon of dendritic flux penetration in superconducting films was studied. Flux dendrites were abruptly formed in a 300 nm thick film of MgB2 by applying a perpendicular magnetic field. Detailed measurements of flux density distributions show that there exists a local threshold field controlling the nucleation and termination of the dendritic growth. At 4 K the local threshold field is close to 12 mT in this sample, where the critical current density is 10^7 A/cm^2. The dendritic instability in thin films is believed to be of thermo-magnetic origin, but the existence of a local threshold field, and its small value are features that distinctly contrast the thermo-magnetic instability (flux jumps) in bulk superconductors.

6 pages, 6 figures, submitted to Phys. Rev. B

References in corpus (7)

• MgB2 superconducting thin films with a transition temperature of 39 Kelvin
• Dendritic magnetic instability in superconducting MgB2 films
• Strong Electron-Phonon Coupling in Superconducting MgB${}_2$: A Specific Heat Study
• Suppression of Superconducting Critical Current Density by Small Flux Jumps in $Mg{B}_2$ Thin Films
• Dendritic flux patterns in MgB2 films
• Vortex avalanches and magnetic flux fragmentation in superconductors
• Current-induced dendritic magnetic instability in superconducting MgB2 films

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• From the second magnetization peak to peak effect. A study of superconducting properties in Nb films and MgB2 bulk samples
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• Evidence of rf-driven branching of dendritic vortex avalanches in MgB2 microwave resonators
• Paramagnetic reentrance of the ac-screening: Evidence of vortex avalanches in Pb thin films
• Flux Dendrites of Opposite Polarity in Superconducting MgB${}_2$ rings observed with magneto-optical imaging
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