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@PHDTHESIS{Gang:864489,
      author       = {Gang, Seung-gi},
      title        = {{E}lement-{S}elective {I}nvestigation of {F}emtosecond
                      {S}pin {D}ynamics in {N}i$_{x}${P}d$_{1-x}$ {M}agnetic
                      {A}lloys using {E}xtreme {U}ltraviolet {R}adiation},
      volume       = {58},
      school       = {Universität Duisburg},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek Verlag},
      reportid     = {FZJ-2019-04266},
      isbn         = {978-3-95806-411-9},
      series       = {Schriften des Forschungszentrums Jülich. Reihe Information
                      / Information},
      pages        = {93, XX S.},
      year         = {2019},
      note         = {Dissertation, Universität Duisburg, 2019},
      abstract     = {Since Beaurepaire et al. discovered optically induced
                      ultrafast magnetization dynamics in Ni thin films in 1996, a
                      variety of experimental and theoretical studies have been
                      made to understand the underlying physical mechanism of the
                      magnetization dynamics. Among the suggested mechanisms,
                      spin-ip electron-phonon scattering described by the
                      microscopic three-temperature model (M3TM)[3] and
                      superdiffusive spin transport[4],[5] are currently
                      considered to be major physical mechanisms contributing
                      substantially to the ultrafast spin dynamics. It is believed
                      that more than one mechanism is responsible for the
                      dynamics. The analysis of magnetization dynamics in
                      Ni$_{x}$Pd$_{1-x}$ alloys with varying composition presented
                      in this thesis provides deeper insight into the relation
                      between the spin dynamics and spin-orbit coupling (SOC) in
                      these materials. Our measurements were mostly done in the
                      transversal magneto-optic Kerr effect (T-MOKE) geometry. To
                      measure ultrafast magnetization dynamics with element
                      selectivity, femtosecond pulses in the extreme ultraviolet
                      (XUV) regime have been produced by laser-based high-order
                      harmonic generation (HHG) in a noble gas. The XUV light from
                      neon gas with an energy range from 20 to 72 eV covering the
                      M$_{2,3}$-edges of ferromagnetic materials (52.7 eV for Fe,
                      58.9 eV for Co, and 68, 66.2 eV for Ni) can be expanded to
                      form a spectrum, by a optical grating introduced on the
                      sample surface. The magnetic contrast and the
                      optically-induced dynamic response can be obtained using XUV
                      light with energy corresponding to the absorption edges of
                      the involved elements. In the Ni$_{x}$Pd$_{1-x}$ alloys, the
                      intrinsically paramagnetic Pd is expected to be magnetically
                      coupled to ferromagnetic Ni via complex exchange paths. One
                      can study spin dynamics in the paramagnetic material (Pd)
                      with induced magnetic moment as a consequence of the
                      exchange coupling with ferromagnetic material (Ni). In
                      addition, element selective measurements allow investigation
                      of questions related to a possible superdiffusive spin
                      transport between the Ni and Pd subsystems. The influence of
                      the increased SOC on the spin dynamics in the
                      Ni$_{x}$Pd$_{1-x}$ alloys can be also investigated by
                      varying the mixing ratio of Ni and Pd in the alloy system.
                      From static T-MOKE, we experimentally confirmed that
                      increasing the Pd content in the alloy gives rise to a
                      pronounced magnetic asymmetry of a bipolar shape at the Pd
                      N$_{3}$-absorption edge (50.9 eV). Varying the mixing ratio
                      in the Ni$_{x}$Pd$_{1-x}$ alloy changes the magnetic
                      properties such as the magnetic moment $\mu$, the Curie
                      temperature T$_{C}$, and the spin-flip scattering
                      probability a$_{sf}$ of the alloy. We show that these
                      parameters are closely related to the magnetization
                      dynamics. Especially, the spin-flip scattering probability
                      a$_{sf}$ scales with the atomic number Z as a$_{sf}
                      \varpropto Z^{4}$ due to SOC. The magnetization dynamics in
                      the Ni$_{x}$Pd$_{1-x}$ alloys can be tuned by the alloy
                      stoichiometry due to a considerable difference in atomic
                      numbers of Ni (Z$_{Ni}$=28) and Pd (Z$_{Pd}$=46). Our
                      results can then be explained by considering the spin-flip
                      scattering probability a$_{sf}$ within the framework of
                      M3TM, and point to the crucial role of the Pd-mediated SOC
                      in optically-induced spin dynamics in the Ni$_{x}$Pd$_{1-x}$
                      alloys.},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {522 - Controlling Spin-Based Phenomena (POF3-522)},
      pid          = {G:(DE-HGF)POF3-522},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/864489},
}