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@INPROCEEDINGS{Sun:906825,
      author       = {Sun, Xiao and Tayal, A. and Dippel, A.-C. and Petracic, O.},
      title        = {{T}uning the structural and magnetic properties of iron
                      oxide nanoparticles},
      reportid     = {FZJ-2022-01719},
      year         = {2022},
      abstract     = {Due to their biocompatibility and magnetic properties, iron
                      oxide nanoparticles (NPs) areespecially interesting for
                      applications such as targeted drug delivery and hyperthermia
                      therapy[1–3]. According to its oxidation states, iron may
                      form various crystal structures and thus showdifferent
                      magnetic properties. Divalent FeO is a bulk antiferromagnet
                      with a rock salt crystalstructure at room temperature. When
                      Fe2+ is oxidized towards the trivalent state, as found e.g.
                      inFe3O4 and Fe2O3, one encounters a spinel structure and
                      ferrimagnetic (FiM) behavior. The FiM toparamagnetic phase
                      transition for bulk magnetite and maghemite occurs at TC =
                      858K and 948K,respectively. However, they may show different
                      magnetic properties in nanoscale due to thefinite size
                      effect. Synthesis of single-phase oxide NPs is challenging.
                      An oxidized layer is oftenfound at the surface of the NPs.
                      This leads to an exchange bias effect.We observe a shift in
                      the hysteresis loops of various sizes of iron oxide NPs
                      (5-20nm). This isdue to an exchange interaction between the
                      magnetite core and a shell with disordered surfacespins. By
                      comparing hysteresis loops cooled at different magnetic
                      fields, a hardening effect isobserved, i.e. the squareness
                      and hardness of hysteresis loops is significantly enhanced
                      withincreasing magnetic cooling field. This indicates that
                      an anisotropy axis is induced due to theexchange bias
                      effect.In order to understand the origin of the exchange
                      bias effect, we studied their crystallographicstructure
                      using X-ray powder diffraction, total scattering experiments
                      with pair distributionfunction analysis. The ratio of
                      different phases of iron oxide (wustite, magnetite and
                      maghemite)was obtained using X-ray absorptions spectroscopy.
                      The morphology of the particles wascharacterized using
                      scanning electron microscopy and small angle scattering. The
                      relationshipbetween the composition of the NPs and the
                      exchange bias effect is studied. Furthermore, themagnetic
                      properties of the samples can be tuned by oxidation or
                      reduction via differentannealing procedures. These results
                      provide important information for the manipulation of
                      theexchange bias in oxide NPs.},
      month         = {Mar},
      date          = {2022-03-14},
      organization  = {30th annual meeting of the German
                       Crystallographic Society (DGK), Ludwig
                       Maximilians Universität München +
                       online (Germany + online), 14 Mar 2022
                       - 17 Mar 2022},
      cin          = {JCNS-2 / PGI-4 / JARA-FIT},
      cid          = {I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {632 - Materials – Quantum, Complex and Functional
                      Materials (POF4-632) / 6G4 - Jülich Centre for Neutron
                      Research (JCNS) (FZJ) (POF4-6G4)},
      pid          = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G4},
      typ          = {PUB:(DE-HGF)1},
      url          = {https://juser.fz-juelich.de/record/906825},
}