Gupta, Anurag and Huhtinen, Hannu and -, Chandra Shekhar and Schlesier, Kim and Srivastava, Pankaj and Srivastava, Amit and Srivastava, O. N. and Laiho, Reino and Narlikar, A. V. (2010) Occurrence of Superconductivity and Magnetism in Nominally Undoped LaOFeAs. Journal of Superconductivity and Novel Magnetism, 23 (8). pp. 1461-1466. ISSN 1557-1947

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Abstract

Superconductivity in a LaOFeAs system is known to get introduced by F-doping (LaO1−xFxFeAs) even under ambient conditions and oxygen deficiency (LaO1−xFeAs)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 ρ(T,B), magnetic M(T,B) and modulated microwave absorption (MMA) measurements. The ρ(T ) at B = 0 shows a clear superconducting transition with an onset at Tcon ∼ 17 K and a tail-like behavior when R goes to zero at Tc0 ∼ 8 K. In the presence of B, the superconducting transition shifts to lower T with a rate ∼−5.5 and −1.65 T/K, depending on whether the ρ(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 ∼12 K. At T <Tc0 the change in MMA with B shows a low field (B ∼ 1 mT) peak, which vanishes at T >Tc0, 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, ρ(T ) reveals a weak SDW-like anomaly at T ∼ 132 K along with a resistivity minimum at Tmin ∼ 78 K. M(T ) also shows the presence of a magnetic anomaly at T ∼ 130 K. Both below and above Tcon, 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.

Item Type:	Article
Additional Information:	Copyright for this article belongs to Springer Verlag
Subjects:	Physics
Divisions:	UNSPECIFIED
Depositing User:	Ms Neetu Chandra
Date Deposited:	18 Jun 2012 08:21
Last Modified:	18 Jun 2012 08:21
URI:	http://npl.csircentral.net/id/eprint/268

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