Publications by authors named "Dieter Engel"

12 Publications

  • Page 1 of 1

The patterning toolbox FIB-o-mat: Exploiting the full potential of focused helium ions for nanofabrication.

Beilstein J Nanotechnol 2021 6;12:304-318. Epub 2021 Apr 6.

Corelab Correlative Microscopy and Spectroscopy, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.

Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3762/bjnano.12.25DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8042487PMC
April 2021

Observation of fluctuation-mediated picosecond nucleation of a topological phase.

Nat Mater 2021 Jan 5;20(1):30-37. Epub 2020 Oct 5.

European XFEL, Schenefeld, Germany.

Topological states of matter exhibit fascinating physics combined with an intrinsic stability. A key challenge is the fast creation of topological phases, which requires massive reorientation of charge or spin degrees of freedom. Here we report the picosecond emergence of an extended topological phase that comprises many magnetic skyrmions. The nucleation of this phase, followed in real time via single-shot soft X-ray scattering after infrared laser excitation, is mediated by a transient topological fluctuation state. This state is enabled by the presence of a time-reversal symmetry-breaking perpendicular magnetic field and exists for less than 300 ps. Atomistic simulations indicate that the fluctuation state largely reduces the topological energy barrier and thereby enables the observed rapid and homogeneous nucleation of the skyrmion phase. These observations provide fundamental insights into the nature of topological phase transitions, and suggest a path towards ultrafast topological switching in a wide variety of materials through intermediate fluctuating states.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41563-020-00807-1DOI Listing
January 2021

A tabletop setup for ultrafast helicity-dependent and element-specific absorption spectroscopy and scattering in the extreme ultraviolet spectral range.

Rev Sci Instrum 2020 Sep;91(9):093001

Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Straße 2A, 12489 Berlin, Germany.

Further advances in the field of ultrafast magnetization dynamics require experimental tools to measure the spin and electron dynamics with element-specificity and femtosecond temporal resolution. We present a new laboratory setup for two complementary experiments with light in the extreme ultraviolet (XUV) spectral range. One experiment is designed for polarization-dependent transient spectroscopy, particularly for simultaneous measurements of magnetic circular dichroism (MCD) at the 3p resonances of the 3d transition metals Fe, Co, and Ni. The second instrument is designed for resonant small-angle scattering experiments with monochromatic light allowing us to monitor spin dynamics with spatial information on the nanometer scale. We combine a high harmonic generation (HHG) source with a phase shifter to obtain XUV pulses with variable polarization and a flux of about (3 ± 1) × 10 photons/s/harmonic at 60 eV at the source. A dedicated reference spectrometer effectively reduces the intensity fluctuations of the HHG spectrum to below 0.12% rms. We demonstrate the capabilities of the setup by capturing the energy- and polarization-dependent absorption of a thin Co film as well as the time-resolved small-angle scattering in a magnetic-domain network of a Co/Pt multilayer. The new laboratory setup allows systematic studies of optically induced spin and electron dynamics with element-specificity, particularly with MCD as the contrast mechanism with femtosecond temporal resolution and an unprecedented signal-to-noise ratio.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/5.0013928DOI Listing
September 2020

Spatial distribution of electric-field enhancement across the gap of terahertz bow-tie antennas.

Opt Express 2020 Aug;28(17):24389-24398

The electric-field enhancement in terahertz (THz) antennas designed for nonlinear THz spectroscopy of soft matter is characterized by spatially resolved electrooptic sampling. To mimic the relevant interaction geometry, metallic, resonant bow-tie antennas are deposited on a thin zinc telluride crystal of 10 µm thickness. The THz electric field transmitted through the antenna gap is recorded by electrooptic sampling. By focusing the 800 nm, sub-20 fs sampling pulses, we achieve a spatial resolution of some 3 µm, which is 1/3 to 1/8 of the antenna-gap width. The THz field in the gap displays an enhancement by a factor of up to 4.5 with a pronounced spectral variation, depending sensitively on the antenna-arm length and the gap width. By scanning the 800 nm probe spot laterally through the antenna gap, the spatial variation of the enhancement is determined, reaching the highest values at the edges of the gap. The results are in agreement with simulations of the electric-field distributions by finite-element calculations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OE.399462DOI Listing
August 2020

Optical inter-site spin transfer probed by energy and spin-resolved transient absorption spectroscopy.

Nat Commun 2020 Feb 13;11(1):871. Epub 2020 Feb 13.

Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Strasse 2A, 12489, Berlin, Germany.

Optically driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. In the present work, we show that such an optical inter-site spin transfer (OISTR) from Pt to Co emerges as a dominant mechanism governing the ultrafast magnetization dynamics of a CoPt alloy. To demonstrate this, we perform a joint theoretical and experimental investigation to determine the transient changes of the helicity dependent absorption in the extreme ultraviolet spectral range. We show that the helicity dependent absorption is directly related to changes of the transient spin-split density of states, allowing us to link the origin of OISTR to the available minority states above the Fermi level. This makes OISTR a general phenomenon in optical manipulation of multi-component magnetic systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-14691-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7018696PMC
February 2020

Single-step fabrication of surface waveguides in fused silica with few-cycle laser pulses.

Opt Lett 2019 Sep;44(17):4267-4270

Direct laser writing of surface waveguides with ultrashort pulses is a crucial achievement towards all-laser manufacturing of photonic integrated circuits sensitive to their environment. In this Letter, few-cycle laser pulses (with a sub-10 fs duration) are used to produce subsurface waveguides in a non-doped, non-coated fused-silica substrate. The fabrication technique relies on laser-induced microdensification below the threshold for nanopore formation. The optical losses of the fabricated waveguides are governed by the optical properties of the superstrate. We have measured losses ranging from less than 0.1 dB/mm (air superstrate) up to 2.8 dB/mm when immersion oil is applied on top of the waveguide.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.44.004267DOI Listing
September 2019

Fast current-driven domain walls and small skyrmions in a compensated ferrimagnet.

Nat Nanotechnol 2018 12 17;13(12):1154-1160. Epub 2018 Sep 17.

Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.

Spintronics is a research field that aims to understand and control spins on the nanoscale and should enable next-generation data storage and manipulation. One technological and scientific key challenge is to stabilize small spin textures and to move them efficiently with high velocities. For a long time, research focused on ferromagnetic materials, but ferromagnets show fundamental limits for speed and size. Here, we circumvent these limits using compensated ferrimagnets. Using ferrimagnetic Pt/GdCo/TaO films with a sizeable Dzyaloshinskii-Moriya interaction, we realize a current-driven domain wall motion with a speed of 1.3 km s near the angular momentum compensation temperature (T) and room-temperature-stable skyrmions with minimum diameters close to 10 nm near the magnetic compensation temperature (T). Both the size and dynamics of the ferrimagnet are in excellent agreement with a simplified effective ferromagnet theory. Our work shows that high-speed, high-density spintronics devices based on current-driven spin textures can be realized using materials in which T and T are close together.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41565-018-0255-3DOI Listing
December 2018

Field-free deterministic ultrafast creation of magnetic skyrmions by spin-orbit torques.

Nat Nanotechnol 2017 11 2;12(11):1040-1044. Epub 2017 Oct 2.

Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Magnetic skyrmions are stabilized by a combination of external magnetic fields, stray field energies, higher-order exchange interactions and the Dzyaloshinskii-Moriya interaction (DMI). The last favours homochiral skyrmions, whose motion is driven by spin-orbit torques and is deterministic, which makes systems with a large DMI relevant for applications. Asymmetric multilayers of non-magnetic heavy metals with strong spin-orbit interactions and transition-metal ferromagnetic layers provide a large and tunable DMI. Also, the non-magnetic heavy metal layer can inject a vertical spin current with transverse spin polarization into the ferromagnetic layer via the spin Hall effect. This leads to torques that can be used to switch the magnetization completely in out-of-plane magnetized ferromagnetic elements, but the switching is deterministic only in the presence of a symmetry-breaking in-plane field. Although spin-orbit torques led to domain nucleation in continuous films and to stochastic nucleation of skyrmions in magnetic tracks, no practical means to create individual skyrmions controllably in an integrated device design at a selected position has been reported yet. Here we demonstrate that sub-nanosecond spin-orbit torque pulses can generate single skyrmions at custom-defined positions in a magnetic racetrack deterministically using the same current path as used for the shifting operation. The effect of the DMI implies that no external in-plane magnetic fields are needed for this aim. This implementation exploits a defect, such as a constriction in the magnetic track, that can serve as a skyrmion generator. The concept is applicable to any track geometry, including three-dimensional designs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nnano.2017.178DOI Listing
November 2017

Colloidal domain lithography in multilayers with perpendicular anisotropy: an experimental study and micromagnetic simulations.

Nanotechnology 2012 Nov 1;23(47):475303. Epub 2012 Nov 1.

Institute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland.

Currently, much attention is being paid to patterned multilayer systems in which there exists a perpendicular magnetic anisotropy, because of their potential applications in spintronics devices and in a new generation of magnetic storage media. To further improve their performance, different patterning techniques can be used, which render them suitable also for other applications. Here we show that He(+) 10 keV and Ar(+) 100 keV ion bombardment of (Ni(80)Fe(20)-2 nm/Au-2 nm/Co-0.6 nm/Au-2 nm)(10) multilayers through colloidal mask enables magnetic patterning of regularly arranged cylindrical magnetic domains, with perpendicular anisotropy, embedded in a non-ferromagnetic matrix or in a ferromagnetic matrix with magnetization oriented along the normal. These domains form an almost perfect two-dimensional hexagonal lattice with a submicron period and a large correlation length in a continuous and flat multilayer system. The magnetic anisotropy of these artificial domains remains unaffected by the magnetic patterning process, however the magnetization configuration of such a system depends on the magnetic properties of the matrix. The micromagnetic simulations were used to explain some of the features of the investigated patterned structures.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/23/47/475303DOI Listing
November 2012

Plasma ion source for in situ ion bombardment in a soft x-ray magnetic scattering diffractometer.

Rev Sci Instrum 2012 May;83(5):053303

Institute of Physics, EP IV, University of Kassel, Heinrich-Plett-Str.40, 34132 Kassel, Germany.

A new plasma ion source for in situ keV He ion bombardment of solid state samples or thin films was designed and built for ion fluences between 1 × 10(12) and 1 × 10(17) ions/cm(2). The system was designed to be mounted to different diffraction chambers for soft x-ray resonant magnetic scattering. Without breaking the vacuum due to He-ion bombardment, structural and magnetic modifications of the samples can be studied in situ and element specifically.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4718937DOI Listing
May 2012

Asymmetric magnetization reversal of stripe-patterned exchange bias layer systems for controlled magnetic particle transport.

Adv Mater 2011 Dec 3;23(46):5568-73. Epub 2011 Nov 3.

Department of Physics and Center for Interdisciplinary Nanostructure, Science and Technology, University of Kassel, Germany.

Domain wall movement assisted transport of particles: exchange-biased samples with designed stripe-domains show strong stray fields and an asymmetric magnetization reversal. Using these characteristics superparamagnetic particles can be trapped and transported directly on the sample over large-scale areas. High particle velocities, small external fields, and automatically reduced particle clustering allow broad applicability of this transport method.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201103264DOI Listing
December 2011

Colloidal domain lithography for regularly arranged artificial magnetic out-of-plane monodomains in Au/Co/Au layers.

Nanotechnology 2011 Mar 24;22(9):095302. Epub 2011 Jan 24.

Institute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland.

Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, the fabrication of regularly arranged artificial domains in topographically flat films is difficult, since the free energy minimization determines the existence, shape, and regularity of domains. Here we show that keV He(+) ion bombardment of Au/Co/Au layer systems through a colloidal mask of hexagonally arranged spherical polystyrene beads enables magnetic patterning of regularly arranged cylindrical magnetic monodomains with out-of-plane magnetization embedded in a ferromagnetic matrix with easy-plane anisotropy. This colloidal domain lithography creates artificial domains via periodic lateral anisotropy variations induced by periodic defect density modulations. Magnetization reversal of the layer system observed by magnetic force microscopy shows individual disc switching indicating monodomain states.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/22/9/095302DOI Listing
March 2011
-->