Origin of dendritic flux patterns in MgB2 films
نویسندگان
چکیده
The dendritic patterns of magnetic flux motion formed during field penetration into an MgB2 film were observed using magneto-optic imaging. To investigate the origin of the dendrites, experiments were performed where the sample was partially covered with an thermally conducting foil serving as an efficient heat sink. We observed that the dendrites are formed only in areas lacking the thermal conductor. When dendrites develop in the uncovered part they never invade into the covered region. The results strongly suggest that the dendritic instability is thermal in origin. 2001 Published by Elsevier Science B.V.
منابع مشابه
Dendritic magnetic instability in superconducting MgB2 films
– Magneto-optical imaging reveal that below 10 K the penetration of magnetic flux in MgB2 films is dominated by dendritic structures abruptly formed in response to an applied field. The dendrites show a temperature-dependent morphology ranging from quasi-1D at 4 K to large tree-like structures near 10 K. This behaviour is responsible for the anomalous noise found in magnetization curves, and st...
متن کاملDramatic role of critical current anisotropy on flux avalanches in MgB2 films.
Anisotropic penetration of magnetic flux in MgB(2) films grown on vicinal sapphire substrates is investigated using magneto-optical imaging. Regular penetration above 10 K proceeds more easily along the substrate surface steps, the anisotropy of the critical current being 6%. At lower temperatures the penetration occurs via abrupt dendritic avalanches that preferentially propagate perpendicular...
متن کاملEffects of the sintering temperature on the flux-pinning mechanism and the activation energy of malic-acid doped MgB2
The flux-pinning mechanism and activation energy of 10 wt % malic acid-doped MgB2 were investigated by measuring of the critical current density and resistivity as a function of magnetic field and temperature. A crossover field, Bsb, was observed from the single vortex to the small vortex bundle pinning regime. For the sintered sample, the temperature dependence of Bsb(T) at low temperature i...
متن کاملDynamics of the dendritic flux instability in YBa2Cu3O7-δ films
– We have studied the dynamics of magnetic-flux avalanches in superconducting YBa2Cu3O7−δ films by means of a fast magneto-optic pump-probe technique. Two regimes of propagation are found: in regime I, directly after the nucleation of the avalanches by a femtosecond laser pulse, the velocity v of the flux dendrites depends strongly on the magnetic field, and values of v up to 180 km/s are obser...
متن کاملThermally activated current transport in MgB2 films
Thermally-activated flux flow (TAFF) resistivity above the irreversibility field Bi is reported for two different c-axis textured MgB2 superconducting films. Transport measurements at different perpendicular magnetic fields 0,B,9 T and temperatures from 5 to 40 K reveal TAFF Ohmic resistivity rsT ,Bd for B.Bi described by the Arrhenius law, r=r0 exps-U /Td with the quadratic field dependence of...
متن کامل