Si-induced superconductivity and structural transformations in DyRh4B4

DyRh4B4 has been known to crystallize in the primitive tetragonal (pt)-structure and to exhibit a ferromagnetic transition at 12 K, the highest magnetic transition temperature in the entire series of the RRh4B4 materials [1]. We show here that our silicon-added samples of the nominal composition DyRh4B4Si0.2 exhibit superconductivity below Tc ~ 4.5 K and an antiferromagnetic transition below TN ~ 2.7 K. The 12 K transition observed in the pt-DyRh4B4 is completely suppressed. Our annealed samples mainly consist of domains of the chemical composition DyRh3.9B4.2Si0.08. These domains contain two crystallographic phases belonging to the body-centred tetragonal (bct)-structure and the orthorhombic (o)-structure. We have reasons to suggest that superconductivity and antiferromagnetic ordering arise from bct- DyRh4B4 phase and, therefore, coexist below TN ~ 2.7 K.Comment: 11 pages, 6 figures, Accepted for publication in Journal of Alloys and Compound

Magnetic properties of Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals

Magnetic properties were studied for the high quality Al-free orthorhombic Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals (0<=x<=1.0) grown by the flux method. An indication on the interaction between the Pr and Cu(2) magnetic sublattices was found for Pr123. Different signs of magnetic anisotropy were established for the Pr and Gd ions at low temperatures. It was also shown that superconductivity reported by Zou et al. [Phys. Rev. Lett. 80 (1998) 1074] for Pr123 single crystals grown by TSZF method seems to be connected with partial substitution of Ba for the Pr-sites.Comment: 2 pages (LaTeX2e), 4 EPS figures, phbauth style file included. LT22 conference paper accepted to Physica

Is U3Ni3Sn4 best described as near a quantum critical point?

Although most known non-Fermi liquid (NFL) materials are structurally or chemically disordered, the role of this disorder remains unclear. In particular, very few systems have been discovered that may be stoichiometric and well ordered. To test whether U3Ni3Sn4 belongs in this latter class, we present measurements of the x-ray absorption fine structure (XAFS) of polycrystalline and single-crystal U3Ni3Sn4 samples that are consistent with no measurable local structural disorder. We also present temperature-dependent specific heat data in applied magnetic fields as high as 8 T that show features that are inconsistent with the antiferromagnetic Griffiths' phase model, but do support the conclusion that a Fermi liquid/NFL crossover temperature increases with applied field. These results are inconsistent with theoretical explanations that require strong disorder effects, but do support the view that U3Ni3Sn4 is a stoichiometric, ordered material that exhibits NFL behavior, and is best described as being near an antiferromagnetic quantum critical point.Comment: 9 pages, 8 figures, in press with PR

The role of carbon for superconductivity in MgCx_{x}Ni3_{3} from specific heat

The influence of carbon deficiency on superconductivity of MgCNi$_{3}$ is investigated by specific heat measurements in the normal and superconducting state. In order to perform a detailed analysis of the normal state specific heat, a computer code is developed which allows for an instantaneous estimate of the main features of the lattice dynamics. By analyzing the evolution of the lattice vibrations within the series and simultaneously considering the visible mass enhancement, the loss in the electron-phonon coupling can be attributed to significant changes of the prominent Ni vibrations. The present data well supports the recently established picture of strong electron-phonon coupling and ferromagnetic spin fluctuations in this compound.Comment: 4 pages, latex, corrections to the text, one reference added, one figure correcte

THORACOSCOPY - DIAGNOSTIC AND THERAPEUTIC OPPORTUNITIES IN SURGICAL CHEST DISEASES

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