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@PHDTHESIS{Nasser:1046811,
      author       = {Nasser, Amal},
      title        = {{S}tructural and {M}agnetic {P}roperties of {B}iocompatible
                      {I}ron {O}xide {N}anoparticles for {M}edical {A}pplications},
      volume       = {296},
      school       = {München},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2025-03970},
      isbn         = {978-3-95806-837-7},
      series       = {Schriften des Forschungszentrums Jülich Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {xii, 140},
      year         = {2025},
      note         = {Dissertation, München, 2025},
      abstract     = {This thesis presents a comprehensive investigation of the
                      structural and magnetic properties of biocompatible iron
                      oxide nanoparticles coated with three different ligand
                      materials: sodium citrate, (3-aminopropyl)triethoxysilane
                      (APTES), and dextran. The influence of the coating agents on
                      the agglomeration of iron oxide nanoparticles and their
                      oxidation stability over time was studied. Various
                      experimental techniques were used to characterize the
                      structural and magnetic properties of the coated
                      nanoparticles, including cryogenic transmission electron
                      microscopy (cryo-TEM), magnetometry, and small-angle X-ray
                      and neutron scattering. The results show that the coatings
                      successfully stabilize the particles leading to various
                      aggregate structures and sizes. These samples exhibit large
                      saturation magnetization levels close to those of bulk iron
                      oxide and a small coercivity as evidenced by the
                      magnetization hysteresis loop at room temperature. We find
                      that the zero-fieldcooled (ZFC) and field-cooled (FC)
                      magnetization behaviour is influenced by magnetic
                      interactions among the nanoparticles inside clusters. The
                      interaction leads to a shift of the blocking temperature to
                      higher values and a flattening of the FC curves at lower
                      temperatures. Notably, the blocking temperature of the
                      citrate-coated samples were lower than would have been
                      expected for the large clustered structure. Furthermore, for
                      this sample magnetic small-angle neutron scattering (SANS)
                      reveals a multidomain structure, with the magnetic size
                      corresponding to half of the cluster size as observed by
                      SAXS. In the aging study, M¨ossbauer spectroscopy was used
                      to follow the changes in Fe2+ and Fe3+ composition over
                      time, while magnetometry allowed the determination of the
                      net magnetization. In all systems, rapid oxidation was
                      observed after less than 0.1 days (the time between the end
                      of synthesis and the sealing of the samples under N2
                      atmosphere). This led to a complete oxidation of the
                      magnetite nanoparticles to maghemite with the dextran
                      coating, while the nanoparticles with citrate and APTES
                      coating showed slower oxidation with $10\%$ - $20\%$ of the
                      magnetite fraction after one month. The variation
                      inoxidation behaviour is linked to the variations in
                      particle size, which in turn are influenced by the coating
                      agent and the synthesis method. Micromagnetic simulations
                      were performed with the Object Oriented Micromagnetic
                      Framework (OOMMF) software for ensembles of randomly
                      arranged and randomly connected nanoparticles. The ”Theta
                      Evolver” within OOMMF was used to include thermal
                      fluctuations of the magnetic superspin moments of the
                      nanoparticles to model the ZFC and FC curves, in addition to
                      the magnetization hysteresis loops. The simulation results
                      help us to understand the effect of exchange and dipolar
                      inter-particle interactions on the energy barriers for
                      magnetization reversal and, thus, on the magnetization
                      hysteresis curves. This knowledge of the altered magnetic
                      behaviour is required in tuning the synthesis route to
                      obtain the desired magnetic properties for future medical
                      applications. Part of the results presented in this thesis
                      was published in Ref. [1], and a secondmanuscript on
                      micromagnetic simulations is in preparation.},
      cin          = {JCNS-4 / JCNS-FRM-II / MLZ},
      cid          = {I:(DE-Juel1)JCNS-4-20201012 /
                      I:(DE-Juel1)JCNS-FRM-II-20110218 / I:(DE-588b)4597118-3},
      pnm          = {6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ)
                      (POF4-6G4) / 632 - Materials – Quantum, Complex and
                      Functional Materials (POF4-632)},
      pid          = {G:(DE-HGF)POF4-6G4 / G:(DE-HGF)POF4-632},
      experiment   = {EXP:(DE-MLZ)TEM-MLZ-20151210 / EXP:(DE-MLZ)SANS-1-20140101},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      doi          = {10.34734/FZJ-2025-03970},
      url          = {https://juser.fz-juelich.de/record/1046811},
}