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Papers by Hans Oepen

Research paper thumbnail of Ultrafast Demagnetization Excited by Extreme Ultraviolet Light From a Free-Electron Laser

Ultrashort and intense extreme ultraviolet (XUV) and X-ray pulses readily available at free-elect... more Ultrashort and intense extreme ultraviolet (XUV) and X-ray pulses readily available at free-electron lasers (FELs) enable studying non-linear light−matter interactions on femtosecond timescales. Here, we report on the non-linear fluence dependence of magnetic scattering of Co/Pt multilayers, using FERMI FEL’s 70-fs-long single and double XUV pulses, the latter with a temporal separation of 200 fs, with a photon energy slightly detuned to the Co M2,3 absorption edge. We observe a quenching in magnetic scattering that sets-in already in the non-destructive fluence regime of a few mJ/cm² typically used for FEL-probe experiments on magnetic materials. Calculations of the transient electronic structure in tandem with a phenomenological modeling of the experimental data by means of ultrafast demagnetization unambiguously show that XUV-radiation-induced demagnetization is the dominant mechanism for the quenching in the investigated fluence regime of <50 mJ/cm², while light-induced chang...

Research paper thumbnail of Direct 2D spatial-coherence determination using the Fourier-analysis method: Multi-parameter characterization of the P04 beamline at PETRA III

Research paper thumbnail of Strain relaxation in high-mobility InAs inserted-channel heterostructures with metamorphic buffer

Physica E: Low-dimensional Systems and Nanostructures

... Samples are grown in a solid source Riber 32P MBE system as is described in detail in Ref. ..... more ... Samples are grown in a solid source Riber 32P MBE system as is described in detail in Ref. ... The authors acknowledge Christian Weichsel and Oliver Kronenwerth for help during transport measurements and the Deutsche Forschungsgemeinschaft for financial support via SFB ...

Research paper thumbnail of Influence of Growth and Structure on the Magnetism of Epitaxial Cobalt Films on Cu(001)

Magnetism and Structure in Systems of Reduced Dimension

Research paper thumbnail of Spatial coherence determination from the Fourier analysis of a resonant soft X-ray magnetic speckle pattern

Research paper thumbnail of Magnetic energies of single submicron permalloy rectangles determined via magnetotransport

Physical Review B Condensed Matter and Materials Physics, Oct 19, 2009

Research paper thumbnail of The reorientation transition in Co/Au(111)

Journal of Applied Physics, Apr 14, 1997

Research paper thumbnail of Controlling the properties of vortex domain walls via magnetic seeding fields

Physical Review B Condensed Matter and Materials Physics, Aug 1, 2010

Research paper thumbnail of Imaging of magentic microstructures at surfaces. The scanning electron microscope with spin polarization analysis

Scanning Microscopy, 1991

Research paper thumbnail of Energy- and spin-analysis of polarized photoelectrons from NEA GaAsP

Appl Phys a Mat Sci Process, 1983

Polarized photoelectrons from NEA GaAs0.6P0.4 are for the first time analysed simultaneously with... more Polarized photoelectrons from NEA GaAs0.6P0.4 are for the first time analysed simultaneously with respect to spin and energy. Parameters of photon energy and temperature were chosen suitable for a polarized electron source cathode. Various contributions to the intensity- and polarization-distribution in connection with several depolarization mechanisms are discussed. Electron-hole exchange scattering together with multiple reflections in the space charge region qualitatively explain the observed distributions. Consequences for a polarized electron source are pointed out.

Research paper thumbnail of Magnetization distribution of 180� domain walls at Fe(100) single-crystal surfaces

Phys Rev Lett, 1989

... In thin films, on the other hand, 1800 Bloch walls are known to yield notoriously low Bitter ... more ... In thin films, on the other hand, 1800 Bloch walls are known to yield notoriously low Bitter contrast. This was explained by La Bonte14 and Hubert,15 who came to the same conclusion on different theoretical grounds: On both surfaces of the film the wall is of Neel-type charac ...

Research paper thumbnail of Magnetization distribution of 180o domain walls at Fe(100) single-crystal surfaces

Physical Review Letters, 1989

Research paper thumbnail of A miniaturized detector for high-resolution SEMPA

Applied Physics a Materials Science Processing, Jan 3, 2003

Research paper thumbnail of Time-resolved scanning electron microscopy with polarization analysis

Applied Physics Letters, 2016

Research paper thumbnail of The effect of tilted edges on the shape anisotropy and stray field coupling of uniformly magnetized rectangular elements

Journal of Applied Physics, Aug 15, 2009

ABSTRACT The influence of tilted edges on the magnetostatic properties of uniformly magnetized th... more ABSTRACT The influence of tilted edges on the magnetostatic properties of uniformly magnetized thin rectangular elements is studied. To calculate the magnetostatic energy, the Poisson equation is solved. The shape of the magnetic element is approximated by horizontally assembled thin cuboids and the solutions of Rhodes and Rowlands [Proc. Leeds Phil. Soc. 6, 191 (1954)] are utilized. A second approach is the straightforward integration of the Poisson equation taking into account the trapezoidal shape of the side faces due to the tilted edges. For an adequate number of cuboids, both methods agree very well. It is found that the shape anisotropy of a single magnetic element with tilted edges is reduced compared to that of an ideal cuboid. For a two element system the shape anisotropy competes with the magnetostatic interaction favoring a magnetization orientation parallel to the connecting line of the elements. If the elements are oriented in-line with their short axes, the easy magnetization axis switches at a critical distance between the elements. This distance increases when the elements have tilted edges.

Research paper thumbnail of Size-dependent magnetic properties in nanoplatelets

Research paper thumbnail of Experimental method for separating longitudinal and polar Kerr signals

Journal of Magnetism and Magnetic Materials, 2000

Research paper thumbnail of Spin polarization of ion excited secondary electrons from ferromagnets

Research paper thumbnail of Lattice-dependent anisotropy in the orientation of magnetic domain walls

Research paper thumbnail of Magnetization reversal in ultrathin Co/Cu(0 0 1)-microstructures

The magnetic domain structure of ultrathin Co-microstructures on Cu(0 0 1) has been investigated ... more The magnetic domain structure of ultrathin Co-microstructures on Cu(0 0 1) has been investigated by means of a scanning electron microscope with polarization analysis. In particular, the influence of a magnetic field on the domain structure has been studied. Here, we concentrate on squares of different size (3-30mm) and variable thickness, although triangles and bars with aspect ratios up to

Research paper thumbnail of Ultrafast Demagnetization Excited by Extreme Ultraviolet Light From a Free-Electron Laser

Ultrashort and intense extreme ultraviolet (XUV) and X-ray pulses readily available at free-elect... more Ultrashort and intense extreme ultraviolet (XUV) and X-ray pulses readily available at free-electron lasers (FELs) enable studying non-linear light−matter interactions on femtosecond timescales. Here, we report on the non-linear fluence dependence of magnetic scattering of Co/Pt multilayers, using FERMI FEL’s 70-fs-long single and double XUV pulses, the latter with a temporal separation of 200 fs, with a photon energy slightly detuned to the Co M2,3 absorption edge. We observe a quenching in magnetic scattering that sets-in already in the non-destructive fluence regime of a few mJ/cm² typically used for FEL-probe experiments on magnetic materials. Calculations of the transient electronic structure in tandem with a phenomenological modeling of the experimental data by means of ultrafast demagnetization unambiguously show that XUV-radiation-induced demagnetization is the dominant mechanism for the quenching in the investigated fluence regime of <50 mJ/cm², while light-induced chang...

Research paper thumbnail of Direct 2D spatial-coherence determination using the Fourier-analysis method: Multi-parameter characterization of the P04 beamline at PETRA III

Research paper thumbnail of Strain relaxation in high-mobility InAs inserted-channel heterostructures with metamorphic buffer

Physica E: Low-dimensional Systems and Nanostructures

... Samples are grown in a solid source Riber 32P MBE system as is described in detail in Ref. ..... more ... Samples are grown in a solid source Riber 32P MBE system as is described in detail in Ref. ... The authors acknowledge Christian Weichsel and Oliver Kronenwerth for help during transport measurements and the Deutsche Forschungsgemeinschaft for financial support via SFB ...

Research paper thumbnail of Influence of Growth and Structure on the Magnetism of Epitaxial Cobalt Films on Cu(001)

Magnetism and Structure in Systems of Reduced Dimension

Research paper thumbnail of Spatial coherence determination from the Fourier analysis of a resonant soft X-ray magnetic speckle pattern

Research paper thumbnail of Magnetic energies of single submicron permalloy rectangles determined via magnetotransport

Physical Review B Condensed Matter and Materials Physics, Oct 19, 2009

Research paper thumbnail of The reorientation transition in Co/Au(111)

Journal of Applied Physics, Apr 14, 1997

Research paper thumbnail of Controlling the properties of vortex domain walls via magnetic seeding fields

Physical Review B Condensed Matter and Materials Physics, Aug 1, 2010

Research paper thumbnail of Imaging of magentic microstructures at surfaces. The scanning electron microscope with spin polarization analysis

Scanning Microscopy, 1991

Research paper thumbnail of Energy- and spin-analysis of polarized photoelectrons from NEA GaAsP

Appl Phys a Mat Sci Process, 1983

Polarized photoelectrons from NEA GaAs0.6P0.4 are for the first time analysed simultaneously with... more Polarized photoelectrons from NEA GaAs0.6P0.4 are for the first time analysed simultaneously with respect to spin and energy. Parameters of photon energy and temperature were chosen suitable for a polarized electron source cathode. Various contributions to the intensity- and polarization-distribution in connection with several depolarization mechanisms are discussed. Electron-hole exchange scattering together with multiple reflections in the space charge region qualitatively explain the observed distributions. Consequences for a polarized electron source are pointed out.

Research paper thumbnail of Magnetization distribution of 180� domain walls at Fe(100) single-crystal surfaces

Phys Rev Lett, 1989

... In thin films, on the other hand, 1800 Bloch walls are known to yield notoriously low Bitter ... more ... In thin films, on the other hand, 1800 Bloch walls are known to yield notoriously low Bitter contrast. This was explained by La Bonte14 and Hubert,15 who came to the same conclusion on different theoretical grounds: On both surfaces of the film the wall is of Neel-type charac ...

Research paper thumbnail of Magnetization distribution of 180o domain walls at Fe(100) single-crystal surfaces

Physical Review Letters, 1989

Research paper thumbnail of A miniaturized detector for high-resolution SEMPA

Applied Physics a Materials Science Processing, Jan 3, 2003

Research paper thumbnail of Time-resolved scanning electron microscopy with polarization analysis

Applied Physics Letters, 2016

Research paper thumbnail of The effect of tilted edges on the shape anisotropy and stray field coupling of uniformly magnetized rectangular elements

Journal of Applied Physics, Aug 15, 2009

ABSTRACT The influence of tilted edges on the magnetostatic properties of uniformly magnetized th... more ABSTRACT The influence of tilted edges on the magnetostatic properties of uniformly magnetized thin rectangular elements is studied. To calculate the magnetostatic energy, the Poisson equation is solved. The shape of the magnetic element is approximated by horizontally assembled thin cuboids and the solutions of Rhodes and Rowlands [Proc. Leeds Phil. Soc. 6, 191 (1954)] are utilized. A second approach is the straightforward integration of the Poisson equation taking into account the trapezoidal shape of the side faces due to the tilted edges. For an adequate number of cuboids, both methods agree very well. It is found that the shape anisotropy of a single magnetic element with tilted edges is reduced compared to that of an ideal cuboid. For a two element system the shape anisotropy competes with the magnetostatic interaction favoring a magnetization orientation parallel to the connecting line of the elements. If the elements are oriented in-line with their short axes, the easy magnetization axis switches at a critical distance between the elements. This distance increases when the elements have tilted edges.

Research paper thumbnail of Size-dependent magnetic properties in nanoplatelets

Research paper thumbnail of Experimental method for separating longitudinal and polar Kerr signals

Journal of Magnetism and Magnetic Materials, 2000

Research paper thumbnail of Spin polarization of ion excited secondary electrons from ferromagnets

Research paper thumbnail of Lattice-dependent anisotropy in the orientation of magnetic domain walls

Research paper thumbnail of Magnetization reversal in ultrathin Co/Cu(0 0 1)-microstructures

The magnetic domain structure of ultrathin Co-microstructures on Cu(0 0 1) has been investigated ... more The magnetic domain structure of ultrathin Co-microstructures on Cu(0 0 1) has been investigated by means of a scanning electron microscope with polarization analysis. In particular, the influence of a magnetic field on the domain structure has been studied. Here, we concentrate on squares of different size (3-30mm) and variable thickness, although triangles and bars with aspect ratios up to

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