Th-substituted SmFeAsO: Structural details and superconductivity with T-c above 50 K

Article

关键词: HIGH-PRESSURE SYNTHESIS;    LAYERED SUPERCONDUCTOR;    MELTING TRANSITION;    CRITICAL CURRENTS;    SINGLE-CRYSTALS;    PHASE-DIAGRAM;    IRON;    MAGNETIZATION;    RE;    LA;   

DOI  :  10.1103/PhysRevB.82.064517

来源: SCIE

【 摘 要 】

We report structural, magnetic, and transport properties of polycrystalline samples and single crystals of superconducting Sm1-xThxFeAsO with maximal T-c above 50 K, prepared under high pressure. Bulk superconducting samples do not undergo a structural phase transition from tetragonal to orthorhombic symmetry at low temperatures. The unit-cell parameters a and c shrink with Th substitution and the fractional atomic coordinate of the As site z(As) remains almost unchanged while that of Sm/Th z(Sm/Th) increases. Upon warming from 5 to 295 K the increase in the FeAs layer thickness is dominant, while the changes in the other structural building blocks are minor, and they compensate each other, since the As-Sm/Th distance contracts by about the same amount as the O-Sm/Th expands. The polycrystalline and single-crystalline samples are characterized by a full diamagnetic response in low magnetic field, by a high intergrain critical current density for polycrystalline samples, and by a critical current density on the order of 8 x 10(5) A/cm(2) for single crystals at 2 K in fields up to 7 T. The magnetic penetration depth anisotropy gamma(lambda) increases with decreasing temperature, in a similar way to that of SmFeAsO1-xFy single crystals. The upper critical field estimated from resistance measurements is anisotropic with slopes of similar to 5.4 T/K (H parallel to ab plane) and similar to 2.7 T/K (H parallel to c axis), at temperatures sufficiently far below T-c. The low-temperature upper critical field anisotropy gamma(H) is in the range of similar to 2, consistent with the tendency of a decreasing gamma(H) with decreasing temperature, previously reported for SmFeAsO1-xFy single crystals.

【 授权许可】

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