Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 7: Superconductivity & Solids At Low Temperature - Poster Session
TT 7.61: Poster
Montag, 27. März 2006, 14:00–17:45, P1
Granularity and Spontaneous Vortex State for the Weakly Ferromagnetic Superconductor RuSr2GdCu2O8 — •Thomas P. Papageorgiou1, Ennio Casini2, Hans F. Braun2, Thomas Herrmannsdörfer1, Andrea D. Bianchi1, and J. Wosnitza1 — 1Hochfeld-Magnetlabor Dresden, Forschungszentrum Rossendorf, D-01314 Dresden, Germany — 2Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
In the high-Tc cuprate RuSr2GdCu2O8 (Ru1212) weak ferromagnetism (TNRu ≃ 130 K) coexists with superconductivity (Tc,onset ≃ 50 K). This rises the interesting question concerning the formation of a spontaneous vortex state (SVS) in the case that the internal magnetic field is greater than the first critical field Hc1. Recently, the formation of a SVS has been proposed for Ru1212 after the phase diagram for this compound was constructed from dc-magnetization and resistance measurements [1]. We show, by a comparison of resistance with ac-susceptibility and dc-magnetization measurements, where both the intra- and inter-granular superconducting transition are obvious, that the granular nature of the investigated samples has to be carefully considered in the investigations of possible SVS formation. A particular SVS with vortices pinned in the intergrain area is much more likely. Single crystals would be required to unambiguously demonstrate the formation or non-formation of a spontaneous vortex state in bulk Ru1212.
[1] C. Y. Yang, B. C. Chang, H. C. Ku, Y. Y. Hsu, cond-mat/0507014