A1 Refereed original research article in a scientific journal
Dependence of Superconductivity and Its Weakly Linked Behavior in Bulk LaO1-xFx FeAs on F Doping
Authors: Gupta A, Huhtinen H, Shekhar C, Schlesier K, Srivastava P, Srivastava A, Srivastava ON, Laiho R, Narlikar AV
Publisher: SPRINGER
Publication year: 2012
Journal: Journal of Superconductivity and Novel Magnetism
Journal name in source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM
Journal acronym: J SUPERCOND NOV MAGN
Number in series: 4
Volume: 25
Issue: 4
First page : 935
Last page: 942
Number of pages: 8
ISSN: 1557-1939
DOI: https://doi.org/10.1007/s10948-011-1394-z
Abstract
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.
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.
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