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@PHDTHESIS{Hamed:891879,
      author       = {Hamed, Mai Hussein Abdalla},
      title        = {{I}nterface {F}unctionalization of {M}agnetic {O}xide
                      {F}e$_{3}${O}$_{4}$/{S}r{T}i{O}$_{3}$ {H}eterostructures},
      volume       = {231},
      school       = {Univerität Duisburg},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2021-01792},
      isbn         = {978-3-95806-535-2},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {xvii, 151 S.},
      year         = {2021},
      note         = {Universität Duisburg, Diss., 2021},
      abstract     = {Oxide heterostructures possess a wide range of electrical
                      and magnetic properties, mainlyvia interactions across their
                      interfaces. The prospect of designing and controlling the
                      magnetic properties at the atomic scale of oxide hetero
                      interfaces is one of the major challenges. In this context,
                      merging transition-metal oxides into heterostructures is
                      very promising, owing to their many remarkable properties,
                      such as emerging conductivities, magnetism or
                      ferroelectricity. Furthermore, iron oxides including FeO,
                      Fe$_{3}$O$_{4}$ and Fe$_{2}$O$_{3}$ polymorphs
                      ($\alpha$Fe$_{2}$O$_{3}$, $\gamma$Fe$_{2}$O$_{3}$...) with a
                      multitude of electric and magnetic functionalities are
                      interesting for many magnetic applications and heterogeneous
                      catalysis. Controlling the oxide interfaces additionally
                      strengthens the manufacturing of functional devices.
                      Therefore, our primary goal is understanding, controlling
                      and tuning the interface properties. For this purpose, we
                      demonstrate the emergence and control of magnetic interfaces
                      between magnetite Fe$_{3}$O$_{4}$, a ferrimagnetic
                      half-metal, and SrTiO$_{3}$, a transparent nonmagnetic
                      insulator which is considered the bedrock of oxide-based
                      electronics. The Verwey transition (T$_{V}$ ) is found to
                      persist from bulk-like down to ultrathin Fe$_{3}$O$_{4}$
                      films, decreasing from 117±4K (38nm) to 25±4K (2nm),
                      respectively. Element-selective electronic and magnetic
                      properties of the ultrathin films and buried interfaces are
                      studied by angle-dependent HAXPES and XMCD techniques. We
                      prove that the SrTiO$_{3}$ substrates induce both strain and
                      interface oxidation. The substrate-induced strain causes the
                      easy axis to switch to [100]. Furthermore, we observe a
                      reduction of Fe2$^{+}$ ions with decreasing film thickness,
                      accompanied by an increase of Fe3$^{+}$ ions in both
                      tetrahedral and octahedral sites, and conclude on the
                      formation of a magnetically active ferrimagnetic 2u.c.
                      $\gamma$Fe$_{2}$O$_{3}$ intralayer. To manipulate the
                      interfacial magnetic phase, a post-annealing process is
                      conducted which causes the reduction of the
                      $\gamma$Fe$_{2}$O$_{3}$ that finally leads to stoichiometric
                      and ferrimagnetic Fe$_{3}$O$_{4}$/SrTiO$_{3}$ (001)
                      heterointerfaces. We demonstrate the thermally induced phase
                      transformations between Fe$_{3}$O$_{4}$,
                      $\gamma$Fe$_{2}$O$_{3}$ and FeO ultrathin iron oxide films,
                      which are part of all-oxide heterostructures, and present a
                      comprehensive thermodynamic analysis of the emerging
                      interfacial redox processes through active redox reactions
                      across three relevant interfaces, i.e. (1) the outside
                      atmosphere/Fe$_{x}$O$_{y}$ film interface, (2) the interface
                      between Fe$_{x}$O$_{y}$/Fe$_{x}$O$_{y}$ intralayers and (3)
                      the Fe$_{x}$O$_{y}$/oxide substrate interface. We thereby
                      reveal the essential – but mostly underrated – role of
                      oxide substrates, which can completely alter the standard
                      FexOy temperature-pressure phase diagram as an additional
                      oxygen supplier or scavenger. We introduce an adjusted phase
                      diagram specifically for Fe$_{x}$O$_{y}$/ Nb:SrTiO$_{3}$ and
                      Fe$_{x}$O$_{y}$ / YSZ heterostructures based on a total
                      effective oxygen activity. Our study goes beyond the current
                      functionalization of oxide heterostructures and their phase
                      transitions. This novel approach opens up the route towards
                      reversible tuning of the physical functionalities, thus, a
                      future integration of Fe$_{3}$O$_{4}$/SrTiO$_{3}$
                      heterostructures into resistive and magnetic switching
                      devices.},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {521 - Quantum Materials (POF4-521)},
      pid          = {G:(DE-HGF)POF4-521},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/891879},
}