A1 Refereed original research article in a scientific journal
Occurrence of Superconductivity and Magnetism in Nominally Undoped LaOFeAs
Authors: Gupta A, Huhtinen H, Shekhar C, Schlesier K, Srivastava P, Srivastava A, Srivastava ON, Laiho R, Narlikar AV
Publisher: SPRINGER
Publication year: 2010
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: 8
Volume: 23
Issue: 8
First page : 1461
Last page: 1466
Number of pages: 6
ISSN: 1557-1939
DOI: https://doi.org/10.1007/s10948-010-0795-8
Abstract
Superconductivity in a LaOFeAs system is known to get introduced by F-doping (LaO1-x F (x) FeAs) even under ambient conditions and oxygen deficiency (LaO1-x FeAs) under high pressure conditions. Hitherto unreported, superconductivity in F-free undoped LaOFeAs samples is observed and confirmed for the first time by various characterization tools-resistive rho(T,B), magnetic M(T,B) and modulated microwave absorption (MMA) measurements. The rho(T) at B=0 shows a clear superconducting transition with an onset at T (con)similar to 17 K and a tail-like behavior when R goes to zero at T (c0 similar to)8 K. In the presence of B, the superconducting transition shifts to lower T with a rate similar to a'5.5 and -1.65 T/K, depending on whether the rho(T) has dropped to 90% or 5% of its normal state value, respectively. M(T) in zero field cooling at B=10 mT shows diamagnetic downturn below at similar to similar to 12 K. At T < T (c0) the change in MMA with B shows a low field (B similar to 1 mT) peak, which vanishes at T > T (c0), indicating the presence of weak link superconducting networks in the sample. The sample shows a complex electrical and magnetic behavior in the normal state. For instance, rho(T) reveals a weak SDW-like anomaly at T similar to 132 K along with a resistivity minimum at T (min) similar to 78 K. M(T) also shows the presence of a magnetic anomaly at T similar to 130 K. Both below and above T (con), presence of an additional ferromagnetic component is observed in the isothermal M(B) loop measurements. The superconducting and normal state features of our sample are compared with other undoped and doped LaOFeAs systems reported in the literature.
Superconductivity in a LaOFeAs system is known to get introduced by F-doping (LaO1-x F (x) FeAs) even under ambient conditions and oxygen deficiency (LaO1-x FeAs) under high pressure conditions. Hitherto unreported, superconductivity in F-free undoped LaOFeAs samples is observed and confirmed for the first time by various characterization tools-resistive rho(T,B), magnetic M(T,B) and modulated microwave absorption (MMA) measurements. The rho(T) at B=0 shows a clear superconducting transition with an onset at T (con)similar to 17 K and a tail-like behavior when R goes to zero at T (c0 similar to)8 K. In the presence of B, the superconducting transition shifts to lower T with a rate similar to a'5.5 and -1.65 T/K, depending on whether the rho(T) has dropped to 90% or 5% of its normal state value, respectively. M(T) in zero field cooling at B=10 mT shows diamagnetic downturn below at similar to similar to 12 K. At T < T (c0) the change in MMA with B shows a low field (B similar to 1 mT) peak, which vanishes at T > T (c0), indicating the presence of weak link superconducting networks in the sample. The sample shows a complex electrical and magnetic behavior in the normal state. For instance, rho(T) reveals a weak SDW-like anomaly at T similar to 132 K along with a resistivity minimum at T (min) similar to 78 K. M(T) also shows the presence of a magnetic anomaly at T similar to 130 K. Both below and above T (con), presence of an additional ferromagnetic component is observed in the isothermal M(B) loop measurements. The superconducting and normal state features of our sample are compared with other undoped and doped LaOFeAs systems reported in the literature.
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