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TT: Fachverband Tiefe Temperaturen

TT 30: Superconductivity - Poster Session

TT 30.37: Poster

Montag, 31. März 2014, 15:00–19:00, P2

Spin Reorientation and Resonance Mode in Ba_1−xNa_xFe₂As₂ — •Florian Waßer¹, Sabine Wurmehl², Saicharan Aswartham², Yvan Sidis³, Astrid Schneidewind^4,5, Ji-Tae Park⁵, Bernd Büchner², and Markus Braden¹ — ¹II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany — ²Institute for Solid State Research, IFW Dresden, D-01171 Dresden, Germany — ³Laboratoire Léon Brillouin, CEA-CNRS, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France — ⁴Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation At MLZ, D-85747, Garching, Germany — ⁵Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM-II), TU München, D-85747 Garching, Germany

Iron-pnictides are a novel class of superconductors displaying a close relation between structure, superconductivity and magnetism. Most parent compounds exhibit a coupled structural and magnetic transition that becomes suppressed upon doping. Here we present our neutron scattering studies on Ba_1−xNa_xFe₂As₂ which differs from the other systems: At intermediate Na concentrations we find clear evidence for a spin reorientation from in-plane to out-of-plane alignment of the ordered moments. The low-temperature phase with c-aligned moments is unique in this system but it qualitatively agrees with the single-ion anisotropy in pure BaFe₂As₂ where it costs less energy to rotate spins from the plane to the c direction than rotating them within the plane. In addition we find a sharp resonance feature in Ba_1−xNa_xFe₂As₂ at low energy and a broader upturn in intensity at energies comparable to those of the resonance values in Co or Ni doped compounds.