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@INPROCEEDINGS{SchmitzAntoniak:818127,
      author       = {Schmitz-Antoniak, Carolin and Warland, Anne and Darbandi,
                      Masih and Schmitz, Detlef and Wende, Heiko},
      title        = {{H}ow the surface affects the electronic and magnetic
                      properties of magnetite nanoparticles},
      reportid     = {FZJ-2016-04643},
      year         = {2016},
      abstract     = {Magnetite (Fe3O4) nanoparticles are objects of intense
                      research activities due to their broad range of applications
                      covering technological, medical, and environmental
                      applications. They are used e.g. for rotary shaft sealing,
                      oscillation damping, position sensing, magnetic inks for jet
                      printing, as contrast agents in magnetic resonance imaging,
                      and to remove heavy metals from wastewater. In addition,
                      magnetite is a half-metal with a predicted negative spin
                      polarisation making magnetite interesting for spintronics.
                      For all applications, a high quality of magnetite is crucial
                      to obtain the desired properties. In this work, we studied
                      the influence of the surface on the electronic and magnetic
                      properties of magnetite nanoparticles by means of x-ray
                      absorption near-edge spectroscopy (XANES) and its associated
                      magnetic circular dichroism (XMCD). In particular, we
                      investigated ensembles of magnetite nanoparticles with a
                      mean diameter of 3nm, 6nm or 9nm and the influence of
                      capping the particles with a 3nm thick silica shell or
                      organic ligands. XANES and XMCD gives the unique possibility
                      to distinguish between the three different Fe species in
                      magnetite, i.e. tetrahedrally coordinated Fe3+ ions,
                      octahedrally coordinated Fe3+, and octahedrally coordinated
                      Fe2+, by using different photon energies for hysteresis
                      measurements. Besides changes in the electronic structure,
                      i.e. in the density of unoccupied 3d states monitored by
                      XANES, and the effective spin magnetic moments, we obtained
                      a different spin canting behaviour of Fe ions in magnetite
                      at different lattice sites from the magnetic field dependent
                      XMCD as shown in the figure below. The results are discussed
                      regarding different exchange mechanisms and possible
                      advantages and drawbacks for applications. Measurements were
                      performed at beamline UE46-PGM1, HZB – BESSY II
                      synchrotron radiation facility. We thank the BESSY II staff
                      for kind support during beamtimes. Financially supported by
                      BMBF (05 ES3XBA/5) and DFG (WE2623/3-1).},
      month         = {Aug},
      date          = {2016-08-22},
      organization  = {8th Joint European Magnetic Symposia,
                       Glasgow (UK), 22 Aug 2016 - 26 Aug
                       2016},
      subtyp        = {After Call},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {522 - Controlling Spin-Based Phenomena (POF3-522)},
      pid          = {G:(DE-HGF)POF3-522},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/818127},
}