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TT: Fachverband Tiefe Temperaturen

TT 28: Superconductivity: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence

TT 28.8: Vortrag

Mittwoch, 25. März 2009, 17:30–17:45, HSZ 105

Magnetic properties and local critical currents of cobalt covered MgB₂ films — •Sebastian Treiber¹ and Joachim Albrecht² — ¹Max Planck Institut für Metallforschung, D-70569 Stuttgart, Germany — ²HTW Aalen, Beethovenstr. 1, D-73430 Aalen, Germany

At Temperatures below 10K the critical state in MgB₂ thin films gets unstable, the magnetic flux percolates filamentary into the superconductor. This state evolves due to chaotic motion of magnetic vortices and leads to dendritic flux density patterns. Since the critical current vanishes inside the dendrites this effect leads to a strong suppression of possible transport currents. We have found, that ferromagnetic cobalt cover layers can influence the flux pinning scenario in the superconductor. Therefore a heterostructure of MgB₂  and cobalt was investigated using SQUID magnetometry and magneto-optical (MO) imaging. Two different effects are observed. On the one hand the temperature for the occurrence of flux avalanches is shifted to lower temperatures as observed by MO studies. On the other hand magnetic hysteresis loops obtained by SQUID measurements show a significant asymmetry with respect to the H_ext = 0 axis attributed to magnetic effects on flux line pinning [1].

[1] S. Treiber, B. Stuhlhofer, H. - U. Habermeier and J. Albrecht, SUST (submitted)