Magneto-optical imaging was used to study a zero-field-cooled film at 9.6K where, in a slowly increasing field, the flux penetrated by the abrupt formation of large dendritic structures. Simultaneously, a gradual flux penetration takes place, eventually covering the dendrites. A detailed analysis of this process was reported. An anomalously high gradient of the flux density across a dendrite branch was found, together with a peak value that decreased as the applied field was increased. This unexpected behavior was reproduced by flux creep simulations which were based upon the non-local field–current relationship in the perpendicular geometry. The simulations also provided indirect evidence that flux dendrites were formed at an elevated local temperature; consistent with a thermo-magnetic mechanism for the instability.

Interplay of Dendritic Avalanches and Gradual Flux Penetration in Superconducting MgB2 Films. D.V.Shantsev, P.E.Goa, F.L.Barkov, T.H.Johansen, W.N.Kang, S.I.Lee: Superconductor Science and Technology, 2003, 16, 566-70