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@INPROCEEDINGS{Angst:891499,
      author       = {Angst, Manuel and Hammouda, Sabreen},
      title        = {{I}mpact of intercalation on magnetism and charge order in
                      rare earth ferrites},
      reportid     = {FZJ-2021-01565},
      year         = {2021},
      abstract     = {Layered rare earth ferrites with active spin and charge
                      degrees of freedom on the iron sites undergo complex
                      ordering processes at relatively high temperature, despite
                      of the geometrical frustration of the lattice. The
                      structurally simplest compounds, with formula RFe2O4 (124),
                      contain Fe/O bilayers, which had been proposed to become
                      polar upon charge ordering leading to an unconventional
                      ferroelectricity, have attracted a lot of interest and were
                      investigated intensely [1]. However, polar bilayers were
                      identified only in one compound, with an anti-polar
                      stacking. The seminar will focus on “intercalated”
                      compounds Lu1+nFe2+nO4+3n, with additional Fe/O single
                      layers inserted between the bilayers. We have grown
                      high-quality single crystals (n=1,2) of these relatively
                      under-investigated compounds and characterized the samples
                      extensively [2]. Magnetization and X-ray Magnetic Circular
                      Dichroism (XMCD) measurements indicate that the local spin
                      arrangement in each individual bilayer is the same as in the
                      not intercalated compound, with the Fe spins in the single
                      layers giving rise to an additional paramagnetic-like
                      contribution [3]. However, magnetic correlations are reduced
                      compared to 124, as also indicated by polarized neutron
                      diffraction [3]. XMCD suggests a similar charge ordering in
                      the bilayers as in 124, confirmed by single-crystal x-ray
                      diffraction: superstructure peaks are observed at positions
                      corresponding to a propagation vector (1/3+,1/3+,0)
                      and symmetry-equivalent, with =0 within error bars in
                      some cases. Structural analysis of the data for Lu2Fe3O7
                      clearly indicated that the 3-fold axis is lost, and further
                      refinements were initially carried out in superspace groups
                      based on Cmcm. The final refinements, which indicate the
                      presence of polytypism of the charge ordered compound, will
                      be discussed in detail. Intriguingly, the results of
                      structural analysis suggest an out-of-plane net
                      polarization, consistent with preliminary piezo-electric
                      force microscopy results.[1] For a review of early work see
                      M. Angst, Phys. Status Solidi RRL 7, 383 (2013).[2] S. S.
                      Hammouda and M. Angst, J. Crystal Growth 521, 50 (2019).[3]
                      S. S. Hammouda, M. Angst, T. Mueller, and E. Weschke, in
                      preparation.},
      month         = {Apr},
      date          = {2021-04-01},
      organization  = {Digital Institute Seminar JCNS-2,
                       online event (online event), 1 Apr 2021
                       - 1 Apr 2021},
      subtyp        = {Invited},
      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)31},
      url          = {https://juser.fz-juelich.de/record/891499},
}