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@PHDTHESIS{Lmker:851019,
      author       = {Lömker, Patrick},
      title        = {{I}nterfacing {E}u{O} in confined oxide and metal
                      heterostructures},
      volume       = {174},
      school       = {Universität Dortmund},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-04733},
      isbn         = {978-3-95806-337-2},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {VI, 140 S.},
      year         = {2018},
      note         = {Dissertation, Universität Dortmund, 2017},
      abstract     = {EuO is a ferromagnetic insulator, a rare material class
                      combining ferromagnetic properties and insulating electronic
                      behavior. We synthesize EuO on SrTiO$_{3}$ (001) and other
                      oxides using a novel approach, the redox reaction with the
                      substrate. For this we develop aquantitative XPS fitting
                      routine on the basis of a set of Eu $\textit{3d}$ reference
                      spectra. The redox growth is possible for T$_{S}$ = 300
                      $^\circ$C-600 $^\circ$C, where we detect stoichiometric EuO
                      exceptfor a small interfacial region. The growth rate was
                      evaluated and we find a Mott-Cabrera like growth limited by
                      ionic oxygen conductivity of the substrate. The crystal
                      structureis analyzed and epitaxial integration of
                      EuO(110)/SrTiO$_{3}$ (100) and EuO(001)/SrTiO$_{3}$(001) is
                      obtained. We detect bulk-like magnetic properties and a
                      maximal thickness of $\textit{d} \approx$ 15 nm for this
                      growth method. The proposed growth method reduces the
                      complexity, as the necessity to calibrate the oxygen
                      pressure is circumvented. For films $\textit{d}$ > 15 nm the
                      well known adsorption limited deposition method can be
                      employed after the redox growth. The electric properties of
                      EuO/oxide and EuO/metal heterostructures are analyzed.
                      Performing ARPES on the EuO/SrTiO$_{3}$ interface, we detect
                      a 2DEG which shows comparable properties as the classical
                      2DEGs like LAO/STO. Our approach provides two novel
                      prospects. First, the preparation of a 2DEG is achieved by a
                      redox-controlled interface reaction and, second, the
                      integration of a ferromagnetic insulator with the 2DEG.
                      Hereby, a 2DEG is prepared in direct contact with a
                      ferromagnet. This interface could be interesting to study
                      the transport properties and elucidate whether the 2DEG is
                      spin-polarized. The integration of EuO with BaTiO$_{3}$ was
                      studied in a second experiment. Again, a 2DEG is created by
                      the redox process between Eu metal and BaTiO$_{3}$. This
                      interface could be of special interest, as other studies
                      have shown BaTiO$_{3}$ to retain its ferroelectric
                      properties at the 2DEG interface, while we find that
                      $\textit{d}_{EuO}$ = 2ML exhibits sizable magnetic
                      properties. This combination with a 2DEG at the interface
                      could pave the way towards a multiferroic device, as the
                      EuO/BaTiO$_{3}$ interface could influence the magnetic
                      properties as a function of the ferroelectric polarization.
                      The EuO/Pt interface reveals the opposite electric effect.
                      Here a 2DHG is predicted by theoretical modeling and we
                      measure, with element specific HAX-XMCD and volumetric
                      magnetometry, an enhanced Curie temperature. This can be
                      interpreted as a first sign of a magnetic interaction at the
                      EuO/Pt interface, which leads to the 2DHG. The magnetic
                      properties of Co/EuO heterostructures are studied with XMCD.
                      We find that the sum rules can be applied to this rare earth
                      material. We use this to determine the exchange length at
                      the Co/EuO interface to 2$\lambda_{AFM}$ = (5.6 ± 1.4)nm,
                      which shows, that the effect is localized to the interface
                      and only thin films of EuO will experience the Co/EuO
                      exchange. Measuring a hysteresis loop at room temperature we
                      observe ferromagnetic properties of EuO, far above its bulk
                      $\textit{T}_{C}$ = 69K. We utilize the hysteresis loop to
                      obtain the Co/EuO exchange coupling strength $\textit{J}$ =
                      0.278 meV $\approx$ 5$\textit{J}_{bulk}$. We interpret this
                      behavior as a magnetic proximity effect. A EuO ultra-thin
                      film of $\textit{d}_{EuO}$ = 2ML is prepared at room
                      temperature and the Co/EuO interface is also studied. We
                      obtain comparable results and M(300K) = 1 μB/f.u.. This
                      shows that a ignificant magnetic moment is retained at room
                      temperature even for ultra-thin EuO films. In conclusion, we
                      have developed a novel route to synthesize high quality EuO
                      by utilizing a redox reaction with the substrate. This
                      further enabled us to observe fascinating interfacial
                      phenomena in oxide and metal heterostructures ranging from
                      two-dimensional conductivity to magnetic proximity effect
                      induced room temperature ferromagnetism in EuO. This can
                      open up new directions in EuO related research.},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/851019},
}