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@PHDTHESIS{Price:138736,
      author       = {Price, Stephen},
      title        = {{I}nterplay between magnetism and superconductivity in iron
                      based high temperature superconductors},
      volume       = {77},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2013-04820},
      isbn         = {978-3-89336-921-8},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {196 S.},
      year         = {2013},
      note         = {RWTH Aachen, Diss., 2013},
      abstract     = {In this thesis, magnetic properties of a series of
                      different Fe-based superconducting materials have been
                      studied by means of neutron scattering techniques. Magnetic
                      correlations in underdoped
                      Ba(Fe$_{0.95}$Co$_{0.05}$)$_{2}$As$_{2}$ have been
                      investigated for three phases of the phase diagram. It was
                      possible to detect the spin gap and spin resonance signal,
                      two features of the particle hole excitation spectrum at
                      Q=(0.5, 0.5, 0), characteristic for the superconducting
                      phase. The spin wave excitations present in the ordered
                      phase have been analyzed quantitatively in terms of a linear
                      spin wave model, whereas a spin diffusion model was applied
                      to the collective excitations of the paramagnetic phase.
                      However, it was found that both models can be applied to
                      excitations in all three phases. In optimally doped
                      CaFe$_{0.88}$Co$_{0.12}$AsF, a spin resonance signal was
                      detected as part of the spin excitation spectrum at Q=(0.5,
                      0.5, 0). The observation of the spin resonance signal
                      supports the s± symmetry of the superconducting gap
                      function. In the undoped CaFeAsF compound three dimensional
                      spin wave like excitations of the static Fe-SDW order have
                      been observed at Q$_{AFM}$=(0.5, 0.5, 0.5), for temperatures
                      below T$_{N}$. Above T$_{N}$ and for energies below 20 meV,
                      the spin wave like excitations are replaced by short range
                      two dimensional paramagnetic excitations, which persist up
                      to 270 K. In superconducting FeSe$_{0.5}$Te$_{0.5}$
                      polarized neutron scattering investigations revealed the
                      magnetic nature of the spin resonance signal and the
                      excitation spectrum at Q=(0.5, 0.5, 0) up to 30 meV. The
                      whole excitation spectrum including the spin resonance
                      signal consists of an isotropic distribution of spin
                      excitations with magnetic moments fluctuating in the
                      ab-plane and perpendicular to the ab-plane, $χ^{"}_{ab}$(Q,
                      ω) $\approx$ $χ^{"}_{c}$(Q, ω). In
                      Eu(Fe$_{1−x}$Co$_{x}$)$_{2}$As$_{2}$ and
                      EuFe$_{2}$(As$_{1−x}$P$_{x}$)$_{2}$ the effect of impurity
                      doping on the static order of the magnetic lattice of the
                      Eu$^{2+}$-moments has been studied by means of polarized and
                      non-polarized neutron diffraction experiments. The
                      introduction of cobalt leads to a helical type structure of
                      the Eusublattice with Eu$^{2+}$-moments oriented parallel to
                      the ab-plane. Whereas, partial replacement of arsenic by
                      phosphorous leads to a ferromagnetic type structure and
                      eventually results in a coexistence of long range
                      ferromagnetic order and superconductivity.},
      keywords     = {Dissertation (GND)},
      cin          = {JCNS-2 / PGI-4 / JARA-FIT / JCNS (München) ; Jülich
                      Centre for Neutron Science JCNS (München) ; JCNS-FRM-II},
      cid          = {I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
                      $I:(DE-82)080009_20140620$ /
                      I:(DE-Juel1)JCNS-FRM-II-20110218},
      pnm          = {422 - Spin-based and quantum information (POF2-422) / 424 -
                      Exploratory materials and phenomena (POF2-424) / 542 -
                      Neutrons (POF2-542) / 544 - In-house Research with PNI
                      (POF2-544) / 54G - JCNS (POF2-54G24)},
      pid          = {G:(DE-HGF)POF2-422 / G:(DE-HGF)POF2-424 /
                      G:(DE-HGF)POF2-542 / G:(DE-HGF)POF2-544 /
                      G:(DE-HGF)POF2-54G24},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/138736},
}