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@PHDTHESIS{Fu:22700,
      author       = {Fu, Zhendong},
      title        = {{S}pin {C}orrelations and {E}xcitations in
                      {S}pin-frustrated {M}olecular and {M}olecule-based
                      {M}agnets},
      volume       = {43},
      school       = {RWTH Aachen},
      type         = {Dr. (FH)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-22700},
      isbn         = {978-3-89336-797-9},
      series       = {Schriften des Forschungszentrums Jülich.
                      Schlüsseltechnologien / Key Technologies},
      pages        = {208 S.},
      year         = {2012},
      note         = {Record converted from JUWEL: 18.07.2013; RWTH Aachen,
                      Diss., 2011},
      abstract     = {The present thesis provides extensive investigations on the
                      effect of geometrical spin frustration in both
                      molecular-based spin clusters and infinite pyrochlore
                      lattice, using advanced neutron scattering, DC and AC
                      susceptibilities, and specific heat methods. Clear
                      short-range spin correlations have been observed in the
                      spin-frustrated molecular magnet {Mo$_{72}$Fe$_{30}$} by
                      means of polarized neutron scattering. Simulations of the
                      spin correlations were carried out within a frustrated
                      three-sublattice spin model. The simulations are in
                      reasonable agreement with the differential magnetic cross
                      section measured at 1.5 K. The specific heat of
                      {Mo$_{72}$Fe$_{30}$} was measured down to 60 mK. The
                      low-lying magnetic excitations of {Mo$_{72}$Fe$_{30}$} are
                      identified by the Schottky anomalies in the specific heat
                      data, consistent with the theoretical predictions of quantum
                      rotational band model. The nature of the magnetic ground
                      state of {Mo$_{72}$Fe$_{30}$} can therefore be interpreted
                      within the three-sublattice spin model, where the 30
                      Fe$^{3+}$ spins are divided into three sublattices with
                      equal and coplanar unit vectors each. The low-lying magnetic
                      excitations of single molecular magnet {As$_{6}$V$_{15}$}
                      were determined by means of specific heat measurements down
                      to 60 mK. The resultant energy spectrum agrees with the
                      theoretical predictions of the “three-spin” model and
                      the results of inelastic neutron scattering experiments.
                      Hence the “three-spin” model is a good approach to the
                      magnetic ground state of {As$_{6}$V$_{15}$}. Complicated
                      magnetic behaviors have been observed in the
                      antiferromagnetic pyrochlore Na$_{3}$Co(CO$_{3}$)$_{2}$Cl.
                      The average crystal structure of
                      Na$_{3}$Co(CO$_{3}$)$_{2}$Cl was determined by means of
                      X-ray and neutron powder diffraction measurements. Though
                      there is no site disorder in the Co$^{2+}$ magnetic
                      sublattice, positional disorder may exist in Na and Cl atom
                      sites. The DC and AC susceptibility measurements show a
                      spin-glass-like transition at 4.5 K, and a field- and
                      frequency- independent kink at 17 K. Temperature dependence
                      of the specific heat exhibits a peak at 1.5 K due to a
                      long-range magnetic order, a broad hump at 5 K associated
                      with the spin-glass-like transition, and a very small hump
                      at 17 K. The diffuse neutron scattering with polarization
                      analysis reveals short-range spin correlations dominated by
                      antiferromagnetic coupling over the range of nearest
                      neighbors. Ferromagnetic coupling exists between
                      next-nearest neighbors. Long-range magnetic order below
                      [...]},
      cin          = {PGI-4 / JCNS (München) ; Jülich Centre for Neutron
                      Science JCNS (München) ; JCNS-FRM-II / JCNS-2},
      ddc          = {500},
      cid          = {I:(DE-Juel1)PGI-4-20110106 /
                      I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-2-20110106},
      pnm          = {Grundlagen für zukünftige Informationstechnologien},
      pid          = {G:(DE-Juel1)FUEK412},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/22700},
}