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@PHDTHESIS{Andreas:156001,
      author       = {Andreas, Christian},
      title        = {{M}ultiscale {M}ultimodel {S}imulation of {M}icromagnetic
                      {S}ingularities},
      volume       = {88},
      school       = {Universität Duisburg-Essen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2014-04916},
      isbn         = {978-3-89336-983-6},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {XIX, 188 S.},
      year         = {2014},
      note         = {Universität Duisburg-Essen, Diss., 2014},
      abstract     = {During the last decades, the research on fundamental
                      magnetic structures, like domain walls, spinwaves and
                      vortices, resulted in a detailed understanding of the
                      magnetization dynamics in ferromagnetic materials, without
                      which the development of modern storage devices would not
                      have been possible. On the pathway to this level of
                      understanding micromagnetic simulations played an important
                      role due to their ability to reproduce experimental results
                      in great detail and, especially, to predict magnetic
                      patterns and their dynamic properties. An example of the
                      predictive power is the research field of vortex dynamics.
                      Another fundamental magnetic structure is the Bloch point,
                      which is particularly complex since the description of the
                      processes and energy terms responsible for its formation lie
                      within the scope of the continuum theory of micromagnetism,
                      but the study of its detailed properties requires a
                      different framework. In terms of topology and concerning the
                      exchange energy density, the Bloch point displays a point
                      singularity in the theory of micromagnetism. Bloch points
                      are not a marginal phenomenon; they play, e.g., an important
                      role as transient structures during the switching of vortex
                      cores and reside inside of the archetypal example of vortex
                      domain walls in solid cylindrical nanowires. In the 1960s,
                      E. Feldtkeller and W. Döring described and characterized
                      Bloch points with the then available methods, yet their
                      dynamics eluded a detailed description, since on one hand a
                      large volume is necessary to stabilize a Bloch point
                      structure and on the other hand an atomistic description of
                      its center is required. To solve this problem we developed a
                      multiscale multimodel simulation framework in the context of
                      this thesis, which is able to detect automatically Bloch
                      points as well as other micromagnetically critical
                      structures. In that simulation kit we apply a classical
                      Heisenberg model to the critical regions, while using the
                      framework of micromagnetism for the remaining sample, which
                      is discretized with finite elements. The program allows not
                      only for a static examination of Bloch points residing in a
                      localized Heisenberg approximated region, but also for
                      dynamic simulations due to its ability to detect regions of
                      interest automatically as well as to track them with the
                      multimodel region. The simulations within this thesis focus
                      on ferromagnetic cylindrical nanowires with vortex domain
                      walls. The simulations describe the depinning field
                      necessary to trigger a propagation of the domain wall with
                      the Bloch point in its center and the impact of the relative
                      orientation of the lattice to the Bloch point propagation
                      direction. In addition, we could identify different
                      propagation patterns of the structure consisting of domain
                      wall and Bloch point. In addition to regimes with a
                      continuous domain wall movement, this thesis highlights and
                      discusses several complex modes of domain wall/Bloch point
                      propagation. In particular, we find a propagation regime in
                      which the Bloch point and domain wall propagate with
                      constant velocity above the minimum spin wave phase
                      velocity. This velocity remains constant within a broad
                      interval of external field strength. Using analytic
                      calculations we could ascribe this maximum velocity, which
                      is a feature of potential interest from a technological
                      perspective, to an intrinsic property of the Bloch point.
                      [...]},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/156001},
}