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@PHDTHESIS{Hanke:856628,
      author       = {Hanke, Jan-Philipp},
      title        = {{T}opological properties of complex magnets from an
                      advanced $\textit{ab-initio}$ {W}annier description},
      volume       = {183},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-05994},
      isbn         = {978-3-95806-357-0},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {XI, 173 S.},
      year         = {2018},
      note         = {RWTH Aachen, Diss., 2018},
      abstract     = {Berry phases impart an elegant interpretation of
                      fundamental condensed-matter phenomena as a direct
                      consequence of the electrons' adiabatic evolution under the
                      variation of control parameters. This thesis develops
                      advanced $\textit{ab initio}$ methods based ondensity
                      functional theory and applies them to investigate Berry
                      phase effects in complex magnets, rooting in the global
                      properties of two distinct types of phase spaces. The
                      non-trivial geometry of momentum space manifests in
                      intrinsic contributions to the anomalous Hall effect as well
                      as orbital magnetism in solids. While the former has been
                      subject to intensive research in the past decades, our
                      understanding of orbital magnetism in periodic systems is
                      still at a rather premature stage. Even its
                      quantum-mechanical description was elusive until the recent
                      advent of a rigorous but involved Berry phase theory, the
                      overall importance of which is unclear. To resolve this open
                      question, we implement the modern theory of orbital
                      magnetization within the full-potential linearized
                      augmented-plane-wave method that is known for its high
                      precision. By comparing to a commonly applied but simple
                      local approximation, we uncover in this thesis that the
                      Berry phase theory is crucial to predict reliably orbital
                      magnetism in systems studied extensively in spintronics,
                      including thin magnetic heterostructures and topological
                      magnets. Remarkably, we demonstrate that the emergent
                      magnetic field due to the chiral spin structure of
                      non-coplanar antiferromagnets constitutes an effcient
                      mechanism to lift the orbital degeneracy even in the absence
                      of spin-orbit coupling. In a new class of materials to which
                      we refer as topological orbital ferromagnets, the
                      macroscopic magnetization originates solely from pronounced
                      orbital magnetism due to non-local charge currents. We
                      identify promising candidates of film and bulk systems that
                      realize the predicted topological orbital magnetization,
                      without any reference to correlation or spin-orbit effects.
                      Paving the road towards innovative device architectures, the
                      burgeoning research field of spin-orbitronics exploits
                      relativistic phenomena to control electrically magnetism by
                      means of spin-orbit torques. Only recently, these torques
                      and the related Dzyaloshinskii-Moriya interaction were
                      recognized as innately geometrical effects that originate
                      from the global properties of a $\textit{mixed}$ phase space
                      entangling the crystal momentum with the magnetization
                      direction. However, the effcient treatment of such complex
                      higher-dimensional phase spaces sets a central challenge for
                      $\textit{ab initio}$ theory, calling for advanced
                      computational methods. This demand is met by a generalized
                      Wannier interpolation that we develop here in order to
                      describe Berry phase effects in generic parameter spaces
                      precisely. Using the scheme for spin torques and chiral
                      interactions in magnetic heterostructures, we correlate
                      their microscopic origin with the electronic structure, and
                      elucidate the role of chemical composition and disorder. In
                      addition, the developed formalism enables us to evaluate
                      effciently the dependence of these phenomena on the
                      magnetization direction, revealing large anisotropies in the
                      studied systems. Considering the interplay of magnetism and
                      topology, we uncover that magnetically induced band
                      crossings manifest in prominent magneto-electric responses
                      in magnetic insulators. We introduce the concept of mixed
                      Weyl semimetals to establish novel guiding principles for
                      engineering large spin-orbit torques in topologically
                      complex ferromagnets. Moreover, we show that topological
                      phase transitions in these materials are accompanied by
                      drastic changes of the local orbital chemistry.},
      cin          = {PGI-1 / IAS-1 / JARA-FIT / JARA-HPC},
      cid          = {I:(DE-Juel1)PGI-1-20110106 / I:(DE-Juel1)IAS-1-20090406 /
                      $I:(DE-82)080009_20140620$ / $I:(DE-82)080012_20140620$},
      pnm          = {142 - Controlling Spin-Based Phenomena (POF3-142)},
      pid          = {G:(DE-HGF)POF3-142},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/856628},
}