The Characteristics of the Superconducting and Magnetic Phases in the Polycrystalline Samples of Ruthenocuprates of Nominal Compositions RuSr_(2)GdCu_(2)O_(8), Ru_(0.98)Sr_(2)GdCu_(2)O_(8) and Ru_(0.5)Sr_(2)GdCu_(2.5)O_(8-delta)

摘要

The temperature dependencies of the resistivity for the superconducting ruthenocuprates of nominal compositions RuSr_(2)GdCu_(2)O_(8), Ru_(0.98)Sr_(2)GdCu_(2)O_(8) and Ru_(0.5)Sr_(2)GdCu_(2.5)O_(8-delta) were examined for the magnetic field dependent characteristics of the superconducting transitions. The effect of the insignificant diminishing of the Ru/Cu ratio in parent RuSr_(2)GdCu_(2)O_(8) was confirmed as relevant for the stabilisation of the superconducting phase. Noted differences in the compared characteristics are interpreted for possible inhomogeneous nucleation of the superconducting phase in the parent ruthenocuprate. The phase anisotropy in RuSr_(2)GdCu_(2)O_(8) and Ru_(0.98)Sr_(2)GdCu_(2)O_(8), in presence of the compounds Ru magnetism, appears to be a cause of a significant softening of the H_(c2)(T) phase line. An anomalous lowering of the magnetoresistivity was observed in the approx. 10 K range above the onset of the superconducting transition, which may suggest the presence of enhanced superconducting fluctuations in the samples. The positive magnetic field shift of the temperatures, which limit the magnetore-sistivity and the specific heat signatures of the magnetic ordered state of the Ru sublattice, suggests probing the influence of the ferromagnetic Ru interactions in an effective metallic-like conduction channel present in the samples. Superconducting characteristics of the Ru_(0.5)Sr_(2)GdCu_(2.5)O_(8-delta) reveal a significant contribution of the Gd paramagnetic signal at low temperatures, interpreted for the presence of a significant anisotropy of the superconducting phase. It is concluded that the Ru-Cu substituted phases of ruthenocuprates may present an opportunity to investigate the effectively anisotropic superconducting phase despite its comparatively high T_(c) in the compounds related to the 123-type cuprate superconductor.