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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. Drechsler1 — 1IFW-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).