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Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 31: Superconductivity: Fe-based Superconductors – 122 and 111

TT 31.9: Talk

Tuesday, March 17, 2015, 12:00–12:15, H 2053

Spin-reorientation and Excitations in Ba1−xNaxFe2As2 — •Florian Wasser1, Sabine Wurmehl2, Saicharan Aswartham2, Yvan Sidis3, Astrid Schneidewind4,5, Jitae Park5, Bernd Büchner2, and Markus Braden11II. Physikalisches Institut, D-50937 Köln, Germany — 2Institute for Solid State Research, D-01171 Dresden, Germany — 3Laboratoire Léon Brillouin, F-91191 Gif-sur-Yvette Cedex, France — 4Jülich Centre for Neutron Science, D-85747 Garching, Germany — 5Forschungsneutronenquelle Heinz Maier-Leibnitz, D-85747 Garching, Germany

Single crystals of Ba1−xNaxFe2As2 with 0.25≤ x ≤0.4 have been studied by unpolarised and polarized neutron scattering. Unlike most FeAs-based compounds, Na doped BaFe2As2 exhibits two successive magnetic transitions at intermediate doping. First there is a transition into an antiferromagnetic phase with moments aligned along the plane, but at low temperatures spin reorient towards the c direction. The magnetic anisotropy of FeAs based compounds is thus of the easy plane type. In the range of coexisting antiferromagnetism and superconductivity we find very strong suppression of the ordered moments in the superconducting state. Inelastic experiments reveal a strong and sharp low-energy resonance in a sample with coexisting phases. This mode completely disappears upon increase of the doping and full suppression of the antiferromagnetic order.

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