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@ARTICLE{Lefmann:200791,
      author       = {Lefmann, K. and Jacobsen, H. and Garde, J. and Hedegard, P.
                      and Wischnewski, Andreas and Ancona, S. N. and Jacobsen, H.
                      S. and Bahl, C. R. H. and Theil Kuhn, L.},
      title        = {{D}ynamic rotor mode in antiferromagnetic nanopartciles},
      journal      = {Physical review / B},
      volume       = {91},
      number       = {9},
      issn         = {1098-0121},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {FZJ-2015-03186},
      pages        = {094421},
      year         = {2015},
      abstract     = {We present experimental, numerical, and theoretical
                      evidence for an unusual mode of antiferromagnetic dynamics
                      in nanoparticles. Elastic neutron scattering experiments on
                      8-nm particles of hematite display a loss of diffraction
                      intensity with temperature, the intensity vanishing around
                      150 K. However, the signal from inelastic neutron scattering
                      remains above that temperature, indicating a magnetic system
                      in constant motion. In addition, the precession frequency of
                      the inelastic magnetic signal shows an increase above 100 K.
                      Numerical Langevin simulations of spin dynamics reproduce
                      all measured neutron data and reveal that thermally
                      activated spin canting gives rise to an unusual type of
                      coherent magnetic precession mode. This “rotor” mode can
                      be seen as a high-temperature version of superparamagnetism
                      and is driven by exchange interactions between the two
                      magnetic sublattices. The frequency of the rotor mode
                      behaves in fair agreement with a simple analytical model,
                      based on a high-temperature approximation of the generally
                      accepted Hamiltonian of the system. The extracted model
                      parameters, such as the magnetic interaction and the axial
                      anisotropy, are in excellent agreement with results from
                      Mössbauer spectroscopy.},
      cin          = {ICS-1 / Neutronenstreuung ; JCNS-1},
      ddc          = {530},
      cid          = {I:(DE-Juel1)ICS-1-20110106 / I:(DE-Juel1)JCNS-1-20110106},
      pnm          = {551 - Functional Macromolecules and Complexes (POF3-551) /
                      6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623)
                      / 6215 - Soft Matter, Health and Life Sciences (POF3-621)},
      pid          = {G:(DE-HGF)POF3-551 / G:(DE-HGF)POF3-6G4 /
                      G:(DE-HGF)POF3-6215},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000351426000001},
      doi          = {10.1103/PhysRevB.91.094421},
      url          = {https://juser.fz-juelich.de/record/200791},
}