Unexpected transport and magnetic properties in Y-Ba-Cu-O superconductors

Solid-state reactions of Y(2)O(3), BaCO(3), and CuO mixtures at stoichiometric ratios of YBa(4)Cu(6)O(x) reveal superconducting products having quite interesting and unusual properties. For instance, superconducting transition T(c) at 90K even without annealing in oxygen flow could be observed. Existence of a ferromagnetic-like behavior was recognized at low temperatures and magnetic fields greater than 1 T. Critical current densities are higher than the one expected from a polycrystalline superconductor. In addition, intergranular J(ct)-values obtained from the transport measurements show strong magnetic field dependency. Magnetic fields of similar to 6.4 Oe decrease J(ct) by about 62% in magnitude. These materials seem to be good candidate for a low field sensor in superconducting gaussmeters. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim