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@PHDTHESIS{Wilhelm:903305,
      author       = {Wilhelm, Marek},
      title        = {{P}hotoemission electron microscopy of magneto-ionic
                      effects in {L}a$_{0.7}${S}r$_{0.3}${M}n{O}$_{3}$},
      volume       = {249},
      school       = {Universität Duisburg},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2021-05001},
      isbn         = {978-3-95806-592-5},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {134 S.},
      year         = {2021},
      note         = {Universität Duisburg, Diss., 2021},
      abstract     = {One of the most challenging tasks in future nanoelectronics
                      is the realization of novel low-power consumption devices
                      for the application in non-volatile memories, processing,
                      transduction and sensing units. Electric-field-control of
                      the magnetism, which is based on the
                      $\textit{magnetoelectric}$ (ME) effect, may pave the way
                      towards an alternative concept to Si-based electronics
                      relying on dissipative electrical currents. Numerous studies
                      reported on magnetoelectric materials showing ME coupling
                      via strain, charge carrier doping and interfacial exchange
                      processes. Recently, the field of magneto-ionics received
                      increased attention as the voltage-driven chemical
                      intercalation of ionic species opened a novel route towards
                      the control of magnetism in bulk materials. This thesis
                      reports on electric-field-induced magnetic switching in a
                      La$_{0.7}$Sr$_{0.3}$MnO$_{3}$(LSMO) thin film prototype
                      system. As a strongly correlated magnetic oxide LSMO can
                      appear in multiple magnetic states depending on the
                      prevalent oxidation state of the manganese cations. The
                      migration of oxygen vacancies and the local redistribution
                      of the oxygen concentration profoundly alters the balance of
                      the double-exchange and superexchange interactions between
                      manganese and oxygen ions, thus providing a granular control
                      of chemical, structural and magnetic phase transitions. 10nm
                      thick La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films were epitaxially
                      grown on TiO$_{2}$-terminated Nb(0.5\%):SrTiO$_{3}$ (001)
                      substrates by means of $\textit{pulsed laser deposition}$
                      (PLD). The morphology and the crystal structure were
                      characterized by atomic force microscopy (AFM) and X-ray
                      diffraction (XRD) revealing an epitaxial, single crystalline
                      film and an atomically flat surface. Vibrating sample
                      magnetometry (VSM) and $\textit{X-ray magnetic circular
                      dichroism}$ (XMCD) were used to investigate the magnetic
                      properties. Further, the electronic structure and the
                      chemical properties were probed by $\textit{hard X-ray
                      photoemission spectroscopy}$ (HAXPES) and $\textit{X-ray
                      absorption spectroscopy}$ (XAS). $\textit{Local conductivity
                      atomic force microscopy}$ (LC-AFM) was utilized to
                      electrically modulate the resistance of LSMO thin films. To
                      investigate the micro-scale redox processes present in the
                      electrically modified areas, we performed a combined and
                      element-selective $\textit{X-ray photoemission electron
                      microscopy}$ (XPEEM) study in XAS and XMCD mode. The results
                      demonstrate the direct interplay between resistivity,
                      chemical composition, and magnetic ordering driven by an
                      oxygen exchange process across the LSMO film surface.
                      Significant chemical modifications are observed in the high
                      resistive state, where the incorporation of oxygen vacancies
                      leads to a distinct valence change from Mn$^{3+/4+}$ to
                      Mn$^{2+/3+}$. Further, a direct correlation between oxygen
                      deficiency and a degradation of the ferromagnetic properties
                      is found. In this light, the results of this thesis provide
                      novel insights into the vacancy-driven magneto-ionic control
                      of magnetoelectric oxides for the example LSMO. Moreover,
                      they open up novel routes towards a multiphase-control of
                      physical and chemical properties in magnetic oxides and
                      novel ionotronic devices.},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {5215 - Towards Quantum and Neuromorphic Computing
                      Functionalities (POF4-521)},
      pid          = {G:(DE-HGF)POF4-5215},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/903305},
}