Magneto-optical studies of c-oriented film, with a critical current density of 107A/cm2, revealed a breakdown of the critical state below 10K. Instead of the usual uniform and gradual flux penetration in an applied magnetic field, an abrupt invasion of complex dendritic structures was observed. When the applied field subsequently decreased, similar dendritic structures of the return flux penetrated the film.

Dendritic Flux Patterns in MgB2 Films. T.H.Johansen, M.Baziljevich, D.V.Shantsev, P.E.Goa, Y.M.Galperin, W.N.Kang, H.J.Kim, E.M.Choi, M.S.Kim, S.I.Lee: Superconductor Science and Technology, 2001, 14, 726-8