The superconducting and magnetic states in RuSr2GdCu2O8, based on the magnetic, transport and magneto-caloric characteristics

The article discusses selected properties of the non- and superconducting polycrystalline samples of RuSr2GdCu2O8 and comments the consequences of introducing insignificant sub-stoichiometry of Ru into the nominal formula. The magneto-resistive and the magnetic characteristics are interpreted in favour of the formation of the intrinsically inhomogeneous superconducting phase, which seems to be stabilized along with the structural modifications likely enhanced with the modification of starting stoichiometry. The specific heat data reveals the shift of temperature of the magnetic ordering T_{m}, suggesting the dilution in magnetic sublattice of the Ru moments. The measurements of the magnetic field dependences of the isothermal magnetocaloric coefficient M_{T} show that there is no gain in magnetic entropy in a broad range of the accessed fields and temperatures. Whereas the multi-component character of the probed magnetic system precludes from concluding on the ground state for the Ru ordering, the maximum in M_{T}(H) which occurs at weak magnetic fields for temperature vicinity of T_{m} may reflect dominance of the ferromagnetic type interactions with a constrained correlation range. The literature explored models for the Ru magnetic ordering and possible phase separation in the RuSr2GdCu2O8 are brought into the discussion.Comment: Most of the discussed results conform to the first author's presentations given at XIV Polish National School for Superconductivity (XIV KSN) in October 2009, and at M2S-IX Conference in September 2009. Submitted to the proceedings of XIV KSN

The characteristics of the superconducting and magnetic phases in the polycrystalline samples of ruthenocuprates of nominal compositions RuSr2GdCu2O8, Ru0.98Sr2GdCu2O8 and Ru0.5Sr2GdCu2.5O8-d

The temperature dependencies of the resistivity for the superconducting ruthenocuprates of nominal compositions RuSr2GdCu2O8, Ru0.98Sr2GdCu2O8 and Ru0.5Sr2GdCu2.5O8-d 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 RuSr2GdCu2O8 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 RuSr2GdCu2O8 and Ru0.98Sr2GdCu2O8 , in presence of the compounds Ru magnetism, appears to be a cause of a significant softening of the Hc2(T) phase line. An anomalous lowering of the magneto-resistivity 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 magneto-resistivity and the specific heat signatures of the magnetic ordered state of the Ru sub-lattice, suggests probing the influence of the ferromagnetic Ru interactions in an effective metallic-like conduction channel present in the samples. Superconducting characteristics of the Ru0.5Sr2GdCu2.5O8-d 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 Tc in the compounds related to the 123-type cuprate superconductor.Comment: 12 pages, 9 figures, accepted for publicatio