Gupta, Anurag and Huhtinen, Hannu and Shekhar, Chandra and Schlesier, Kim and Srivastava, Pankaj and Srivastava, Amit and Srivastava, O. N. and Laiho, Reino and Narlikar, A. V. (2012) Dependence of Superconductivity and Its Weakly Linked Behavior in Bulk LaO1-xFx FeAs on F Doping. Journal of Superconductivity and Novel Magnetism, 25 (4). pp. 935-942. ISSN 1557-1939

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Samples of oxypnictide compound LaO1-x F (x) FeAs, with x=0.15 and 0.2 corresponding to over- and highly over-doped compositions, respectively, were prepared by solid-state reaction. We present their characterization by XRD and HRTEM, as well as resistivity rho(T), magnetization M(B) and microwave modulated absorption (MMA) response between 4.2-300 K and applied fields B=0-8 T. With change in x, both the superconducting and magnetic behavior of the samples shows an interesting pattern. The "magnetic anomaly" at T similar to 130 K, observed in M(T) for x=0, instead of getting totally suppressed shows a tendency to reappear in x=0.2 sample. Both samples typically show rho(300 K)> 2.8x10(-3) Omega cm and critical current density J (c)(5 K, 1 T)< 2x10(7) A/m(2). The superconducting transitions as measured by rho(T) at B=0 are found broad for both x=0.15 and 0.2 samples with transition widths similar to 2.5 and 6 K, respectively. The slope |dB (c2)/dT| (where B (c2) is upper critical field) determined by resistive onsets, for the x=0.15 and 0.2 samples, has values similar to 7.5 and 3.5 T/K, respectively. The superconducting state characteristics as reflected by rho(T,B), M(T), magnetic J (c)(B) and MMA response are typical of the presence of weakly linked inter-grain regions in both the samples. Our HRTEM images of the x=0.15 sample show the presence of high angle (similar to 43(a similar to)) grain boundaries, which are well known to limit the J (c) in cuprate-based high T (c) bulk materials.

Item Type: Article
Additional Information: Copyright for this article belongs to M/s Springer Verlag.
Subjects: Applied Physics/Condensed Matter
Depositing User: Users 27 not found.
Date Deposited: 07 Feb 2020 10:28
Last Modified: 07 Feb 2020 10:28

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