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@MASTERSTHESIS{Thoma:859546,
      author       = {Thoma, Henrik},
      title        = {{T}he {S}ign of the {D}zyaloshinskii-{M}oriya {I}nteraction
                      in {R}-3c {S}ymmetries},
      school       = {TUM: Technische Universität München},
      type         = {Masterarbeit},
      reportid     = {FZJ-2019-00398},
      pages        = {90 p.},
      year         = {2018},
      note         = {Masterarbeit, TUM: Technische Universität München, 2018},
      abstract     = {The Dzyaloshinskii–Moriya (DM) interaction is a type of
                      exchange-coupling between twospins that can have significant
                      effects on the properties of magnetic materials. Its
                      magnitudeis usually small, but its direction is often a
                      decisive factor in the determination ofthe system’s
                      chirality. A better understanding of the spin–orbit
                      interaction and its implicationshave been a particular
                      target of condensed matter research over the past
                      decade:multiferroics, topological insulators, and Rashba and
                      Dresselhaus spin–orbit coupling areall intensively
                      studied. Recently in Nature Physics, V. Dmitrienko and
                      colleagues havefound a way to measure the sign of the
                      coupling vector, in order to determine the directionof the
                      DM interaction, using sophisticated techniques based on
                      synchrotron spectroscopy.In this Master thesis, the sign of
                      the DM interaction is determined in hematite
                      (alpha-Fe2O3)and rhodochrosite (MnCO3) single crystals with
                      R-3c symmetry by means of polarizedneutron diffraction
                      (PND).The theoretical basis for the DM interaction, based on
                      a symmetry analysis in both compounds,is introduced. The
                      polarized single crystal diffraction theory and its
                      methodsare briefly presented. A dedicated PND setup, using a
                      new symmetric-field high Tc superconductingmagnet with a
                      maximal field of 2.2T in combination with a 3He polarizerand
                      Mezei-type flipper, has been developed. The corresponding
                      numerical simulationsand optimization for each component are
                      presented and the complete setup is successfullytested and
                      calibrated.This new PND setup is used to collected
                      flipping-ratio (FR) data as function of the appliedmagnetic
                      field and temperature for both compounds. The measured data
                      were evaluatedaccording to the theoretical basis provided in
                      the first part of this thesis. In addition, anadvanced
                      approach for the reconstruction of maximum entropy spin
                      density maps fromFR data is presented and appropriate
                      software tools developed. Using these softwaretools, 3D spin
                      density maps are build for the paramagnetic and
                      antiferromangetic phase,in both compounds for the first
                      time, revealing new features compared to the results
                      fromconventional maximum entropy software.The analysis of
                      the obtained spin density distribution maps showed clearly
                      on one sidethat the origin of the magnetic scattering is not
                      the localized moments at the atomic positions,but rather
                      magnetic fields of the displaced orbitals. On the other
                      side, 3D mapsallowed the extraction of the sign of the DM
                      interaction.},
      cin          = {JCNS-FRM-II / JCNS-2 / JARA-FIT / TUM},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-2-20110106 / $I:(DE-82)080009_20140620$ /
                      I:(DE-588b)36241-4},
      pnm          = {524 - Controlling Collective States (POF3-524) / 6212 -
                      Quantum Condensed Matter: Magnetism, Superconductivity
                      (POF3-621) / 6G15 - FRM II / MLZ (POF3-6G15) / 6G4 - Jülich
                      Centre for Neutron Research (JCNS) (POF3-623)},
      pid          = {G:(DE-HGF)POF3-524 / G:(DE-HGF)POF3-6212 /
                      G:(DE-HGF)POF3-6G15 / G:(DE-HGF)POF3-6G4},
      experiment   = {EXP:(DE-MLZ)POLI-HEIDI-20140101},
      typ          = {PUB:(DE-HGF)19},
      url          = {https://juser.fz-juelich.de/record/859546},
}