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@PHDTHESIS{Bhatnagar:893740,
      author       = {Bhatnagar, Tanvi},
      title        = {{R}esolving interface effects in voltage controlled
                      magnetic heterostructures using advanced neutron scattering
                      and electron microscopy methods},
      volume       = {251},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2021-02795},
      isbn         = {978-3-95806-604-5},
      series       = {Schriften des Forschungszentrums Jülich Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {ix, 171},
      year         = {2021},
      note         = {Dissertation, RWTH Aachen University, 2021},
      abstract     = {Voltage control of magnetism (VCM) shows a strong potential
                      to impact the fieldof magnetic data storage and spintronic
                      devices with low power consumption. Withthis as an aim,
                      La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)O3 - PbTiO3 (LSMO/PMN-PT
                      (001))heterostructure is deposited using oxide molecular
                      beam epitaxy. LSMO is ferromagneticat room temperature.
                      Grown on a piezoelectric /ferroelectric
                      substratePMN-PT(001), it forms an artificial multiferroic
                      heterostructure. This system wasstructurally characterized
                      using different techniques revealing growth of epitaxialLSMO
                      layers. The main part of this thesis focuses on the
                      investigation of magnetoelectriccoupling in
                      LSMO/PMN-PT(001). The measurements show change inthe nature
                      of ME coupling, by varying different parameters like
                      temperature anddirection of magnetization. In all
                      experiments the voltage is applied along [001] direction.The
                      magnetoelectric coupling in LSMO/PMN-PT(001) arises due to
                      strainand charge coupling. Since the substrate PMN-PT is
                      piezoelectric and ferroelectric,both strain effect and
                      switching of ferroelectric polarizations contribute to the
                      MEcoupling. Impact of both mechanism is visible in the
                      measurements. Strain couplingis dominant along hard axis
                      [100] of LSMO whereas charge coupling shows dominancealong
                      easy axis [110] of LSMO. Using polarized neutron
                      reflectometry (PNR),the magnetic depth profile as a function
                      of applied voltage reveals the presence ofan interlayer with
                      reduced nuclear scattering length density and magnetic
                      scatteringlength density. Examining this interlayer with
                      scanning transmission electronmicroscopy (STEM) and energy
                      dispersive X-ray spectroscopy (EDS) shows Ladeficiencyand
                      excess of Mn near the interface with the dark regions to be
                      particleswith a triangular cross-section. The stoichiometry
                      of these particles is confirmedwith field cooled-cooling
                      (FCC) curve which shows a jump in magnetization near
                      theCurie temperature TC = 43K of Mn3O4. The formation of
                      these particles is favoredwhen the LSMO films are strongly
                      strained which leads to defects near the interface.STEM
                      images shows the presence of defects near the interface.
                      Real-space magneticfield mapping as a function of
                      temperature is performed using off-axis electron
                      holographyon LSMO/PMN-PT(001) which demonstrates uniform
                      magnetic field in theLSMO films. The magnetic phase gradient
                      reduces with increasing temperature depictingreduction in
                      the magnetic field in LSMO layer with temperature. Based
                      onsimilar approach, a second heterostructure,
                      La0.7Sr0.3MnO3/ BaTiO3/ Nb:SrTiO3(LSMO/BTO/Nb:STO (001)) is
                      deposited using high oxygen pressure sputteringsystem and
                      oxide molecular beam epitaxy. Here, LSMO is a ferromagnetic
                      component,BTO layer is ferroelectric and Nb:STO is used a
                      conductive substrate. Thegrowth of this structure is a
                      two-step process. The BTO layer is grown in thehigh oxygen
                      pressure sputtering system using growth parameters optimized
                      duringa growth study.},
      cin          = {JCNS-2 / PGI-4 / JARA-FIT},
      cid          = {I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {632 - Materials – Quantum, Complex and Functional
                      Materials (POF4-632) / 6G4 - Jülich Centre for Neutron
                      Research (JCNS) (FZJ) (POF4-6G4)},
      pid          = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G4},
      experiment   = {EXP:(DE-MLZ)MARIA-20140101 / EXP:(DE-MLZ)TREFF-20140101},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/893740},
}