4 research outputs found
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
Specific heat in the superconducting and normal state (2-300 K, 0-16 Teslas), and magnetic susceptibility of the 38-K superconductor MgB2: evidence for a multicomponent gap
The specific heat C of a sintered polycrystalline sample of MgB2 with a bulk
superconducting transition temperature Tc=36.7 K is measured as a function of
the temperature (2-300 K) and magnetic field (0-16 T), together with magnetic
properties (normal-state susceptibility, superconducting state magnetization,
etc.). The Sommerfeld constant gamma=0.89+-0.05 mJ/K^2/gat (2.7 mJ/K^2/mol) is
determined in the normal state above Hc2. The normal- and superconducting state
entropies are equal at Tc. Several moments of the phonon density of states are
obtained from the lattice specific heat. We report bulk values for: the
thermodynamic critical field, the slope of the upper critical field, the
Ginzburg-Landau parameter, the coherence length, the lower critical field, the
London penetration depth. These results characterize MgB2 as a type-II
superconductor. The nearly quadratic dependence of C(T) versus T at T<<Tc, its
non-linear field dependence, and the discrepancy between the electron-phonon
coupling constant lambda_ep as determined by the renormalization of the
electron density-of-states (lambda_ep=0.6) and by McMillan's equation for
isotropic superconductors (lambda_ep=1.1), are inconsistent with a single
isotropic gap. In addition to high phonon frequencies, anisotropy or two-band
gap structure may explain why the critical temperature of this superconductor
is high in spite of its low condensation energy, which does not exceed 1/16 of
that of YBa2Cu3O7 and 1/4 of that of Nb3Sn.Comment: 17 pages, 11 figures, pd
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