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@PHDTHESIS{Wessels:192791,
      author       = {Wessels, Philipp},
      title        = {{T}ime-resolved imaging of magnetic nanostructures in the
                      visible and soft {X}-ray spectral range},
      school       = {Universität Hamburg},
      type         = {Dr.},
      address      = {München},
      publisher    = {Verlag Dr. Hut},
      reportid     = {PUBDB-2014-04317},
      isbn         = {978-3-8439-1815-2},
      year         = {2014},
      note         = {OA; Universität Hamburg, Diss., 2014},
      abstract     = {To unravel the nature of magnetism, an investigation at its
                      fundamental length- and time-scales has to be tackled.
                      Besides pure research interest of the processes occurring in
                      nanoscopic magnetic systems in the femto- and picosecond
                      range, advancing knowledge experiences promising
                      applications toward faster non-volatile memory devices with
                      increased data storage density. However, this exploration
                      demands state-of-the-art experimental setups sensitive to
                      detect the magnetization with superior spatial and temporal
                      resolution. In this work two new instruments for
                      time-resolved imaging of magnetic nanostructures have been
                      set up:A tabletop time-resolved scanning Kerr microscope
                      (TR-SKM) capable of analyzing the dynamics of patterned
                      magnetic media using the magneto-optic Kerr effect (MOKE) in
                      combination with femtosecond laser pulses to carry out
                      stroboscopic pump-probe experiments. With a novel pump
                      approach utilizing a magnesium photocathode as
                      electrooptical switch, the generation of intense, broadband
                      electronic current pulses becomes possible for excitation of
                      magnetic systems with the transported transient magnetic
                      field. This enables jitter-free measurements on isolated
                      spin-wave packets in permalloy (Ni80Fe20) with a temporal
                      resolution < 30 ps and a spatial resolution < 560 nm. The
                      spatially and temporally resolved data set permits a global
                      analysis of the dynamic parameters defining the wave-packet.
                      For the first time, a direct observation of backward volume
                      modes with counterpropagating group and phase velocities in
                      permalloy became possible.For examinations requiring an
                      increased spatial resolution, a mobile synchrotron radiation
                      based full-field time-resolved magnetic transmission X-ray
                      microscope (TR-MTXM) has been set up at the soft X-ray
                      beamline P04 of the high-brilliance storage ring PETRA III
                      at DESY with a temporal resolution < 250 ps and a spatial
                      resolution < 65 nm. The magnetization of a sample is
                      accessible via the X-ray magnetic circular dichroism (XMCD).
                      Experiments to stimulate magnetic permalloy nanostructures
                      with synchronized femtosecond laser pulses as well as
                      picosecond electronic current pulses of large amplitudes
                      have been carried out. Vortex magnetization patterns were
                      forced into a non-equilibrium state by aligning the majority
                      of the magnetic moments into one direction and the evolution
                      of the domain pattern destruction and recovery could be
                      monitored in time. A reproducible recovery of the vortex
                      pattern with stable chirality and polarity and unusually
                      high vortex core velocities could be observed. Feasibility
                      studies on nonreversible switching processes in need of an
                      active reset stimulus in magnetic chains and arrays have
                      been initiated.},
      keywords     = {Dissertation (GND)},
      cin          = {UNI/EXP / FS-PE},
      cid          = {$I:(DE-H253)UNI_EXP-20120731$ / I:(DE-H253)FS-PE-20120731},
      pnm          = {PETRA Beamline P04 (POF2-54G14) / FS-Proposal: I-20120127
                      (I-20120127)},
      pid          = {G:(DE-H253)POF2-P04-20130405 / G:(DE-H253)I-20120127},
      experiment   = {EXP:(DE-H253)P-P04-20150101},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://bib-pubdb1.desy.de/record/192791},
}