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Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 17: SC: Fe-based Superconductors - 1111

TT 17.2: Talk

Monday, March 14, 2011, 18:30–18:45, HSZ 301

Ferromagnetic correlations and Pauli limit behavior of As-deficient LaO0.9F0.1FeAs1−δ — •V. Grinenko1, G. Fuchs1, K. Nenkov1, F. Hammerath1, B. Holzapfel1, K. Kikoin2, and S.-L. Drechsler11IFW-Dresden, D-01171 Dresden, Germany — 2Tel Aviv University, Tel Aviv, Israel

The field and T-dependence of the static magnetic susceptibility χ of As-deficient LaO0.9F00.1FeAs1−δ (with δ 0.05-0.1) and LaO0.9F0.1FeAs is analysed basing on recent 75As NMR spectroscopy data [1]. The analysis of the Curie-like contribution to the spin-lattice relaxation rate T1 and χ(T) together with specific heat data reveals that As vacancies induce local moments. We ascribe the appearance of uncompensated magnetic moment to reconstruction of valence bonds with 4 Fe atoms neighboring to the As-vacancy. These local moments do not suppress superconductivity (Tc increases compared to LaO0.9F0.1FeAs) but contribute to the Pauli susceptibility χP via an enhanced Stoner factor. We estimated an enhanced χP for LaO0.9F0.1FeAs1−δ by a factor of 3-4 in the clean reference sample. This high χP is responsible for the Pauli limiting (PL) behavior observed in As-deficient LaO0.9F0.1FeAs1−δ [2]. A thermodynamic critical field Bc(0)≈ 1T was estimated for LaO0.9F00.1FeAs1−δ , using the measured χ and the PL field Bp(0)=88 T from Bc2(T) data. In contrast, no PL was found for stoichiometric LaO0.9F0.1FeAs which is consistent with its small Pauli susceptibility.
F. Hammerath et al., Phys. B. 88, 140504(R) (2010).
G. Fuchs et al., Phys. Rev. Lett. 101, 237003 (2008).

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