A5053501947- Magnetic properties of thin films
- Quantum and electron transport phenomena
- Magneto-Optical Properties and Applications
- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- ZnO doping and properties
- Magnetic Properties and Applications
- Theoretical and Computational Physics
- Advanced Condensed Matter Physics
- Electronic and Structural Properties of Oxides
- Multiferroics and related materials
- Magnetic Properties of Alloys
- Photonic Crystals and Applications
- Terahertz technology and applications
- Metallic Glasses and Amorphous Alloys
- Copper Interconnects and Reliability
- Advanced Memory and Neural Computing
- Characterization and Applications of Magnetic Nanoparticles
- Advanced Thermodynamics and Statistical Mechanics
- Dendrimers and Hyperbranched Polymers
- GaN-based semiconductor devices and materials
- Cold Atom Physics and Bose-Einstein Condensates
- Nanowire Synthesis and Applications
- Rare-earth and actinide compounds
- Graphene and Nanomaterials Applications
TU Dortmund University
2019
University of Regensburg
2014-2018
Massachusetts Institute of Technology
2009-2015
University of Konstanz
2009-2013
Paul Scherrer Institute
2011-2013
École Polytechnique Fédérale de Lausanne
2011-2013
Vifor Pharma (Switzerland)
2013
We report the experimental observation of Snell's law for magnetostatic spin waves in thin ferromagnetic Permalloy films by imaging incident, refracted, and reflected waves. use a thickness step as interface between two media with different dispersion relations. Since relation is anisotropic, deviations from isotropic known optics are observed incidence angles larger than 25° respect to normal magnetic media. Furthermore, we can show that modifies wavelength amplitude incident Our findings...
Terahertz emission spectroscopy of ultrathin multilayers magnetic and heavy metals has recently attracted much interest. This method not only provides fundamental insights into photoinduced spin transport spin-orbit interaction at highest frequencies but also paved the way to applications such as efficient ultrabroadband emitters terahertz electromagnetic radiation. So far, predominantly standard ferromagnetic materials have been exploited. Here, by introducing a suitable figure merit, we...
We report the experimental observation of spin-orbit torque induced switching perpendicularly magnetized $\mathrm{Pt}/\mathrm{Co}$ elements in a time resolved stroboscopic experiment based on high resolution Kerr microscopy. Magnetization dynamics is by injecting subnanosecond current pulses into bilayer while simultaneously applying static in-plane magnetic bias fields. Highly reproducible homogeneous scales several tens nanoseconds observed. Our findings can be corroborated using...
We report spin wave propagation experiments in thin yttrium iron garnet (YIG) films. Using time-resolved scanning Kerr microscopy we extract the mode structure of waves. For quasi-single-mode excitation, decay can be fitted with a damped harmonic oscillator function providing us information about attenuation length. measure values 2.7 and 3.6 \ensuremath{\mu}m for length 38- 49-nm-thick YIG samples, respectively. Micromagnetic simulations are performed to compare experimental simulated...
Current-induced magnetization dynamics is governed by a subtle combination of damping, adiabatic, and nonadiabatic spin-transfer torques (STTs). A precise determination these three key parameters difficult since they have to be determined in the very same nanostructured sample. In this study, we experimentally determine spin-tansfer torque fully self-consistent approach optically accessing current-induced spin-wave dynamics. Our technique allows access characteristics their changes,...
We investigate the influence of interfacial Dzyaloshinskii-Moriya interaction (DMI) on propagation Damon-Eshbach spin waves in micrometer-sized Pt(2 nm)/Co(0.4 nm)/Py(5 nm)/MgO(5 nm) stripes. use time-resolved scanning Kerr microscopy to image excited by a microwave antenna and directly access their dispersion. The presence an DMI manifests itself asymmetry dispersion for counterpropagating which reverses sign upon reversal direction externally applied magnetic field. From this we deduce...
In optics, a light beam experiences spatial shift in the plane upon total internal reflection. This is usually referred to as Goos-Hänchen shift. When dealing with waves, it manifests itself phase between an incoming and reflected wave that depends on vector component along interface. experiments presented here, spin waves are excited 60-nm-thick Permalloy film propagate towards edge of film. By means time-resolved scanning Kerr microscopy, we able directly detect wave. With help numerical...
We investigate the interplay between governing magnetic energy terms in patterned La0.7Sr0.3MnO3 (LSMO) elements by direct high-resolution x-ray microscopy as a function of temperature and geometrical parameters. show that configurations evolve from multidomain to flux-closure states (favored shape anisotropy) with decreasing element size, thickness-dependent crossover at micrometer scale. The are stable against thermal excitations up near Curie temperature. Our results demonstrate control...
Ferromagnetic carbon-coated cobalt nanoparticles have been ligated by a covalent or non-covalent strategy with dendrons polymers bearing amino-, hydroxy- polyether-functionalities, aiming at synthesizing materials that are dispersible in aqueous solutions, being prerequisite for applications biomedicine. Most efficiently this purpose proved to be covalently anchored polyethyleneimine (PEI) loading of approximately 10 mmol amino groups per gram hybrid nanomaterial, resulting dispersions...
We experimentally demonstrate by time-resolved scanning magneto-optical Kerr microscopy the possibility to locally excite multiple spin-wave beams in dipolar-dominated regime metallic NiFe films. For this purpose we employ differently shaped nonuniform microwave antennas consisting of several coplanar waveguide sections different size, thereby adapting an approach for generation exchange-dominated suggested Gruszecki et al. [Sci. Rep. 6, 22367 (2016)]. The occurring are diffractive and show...
We investigate the incorporation of manganese into self-catalyzed GaAs nanowires grown in molecular beam epitaxy. Our study reveals that Mn accumulates liquid Ga droplet and no significant nanowire is observed. Using a sequential crystallization droplet, we then demonstrate deterministic epitaxial growth MnAs segments at tip. This technique may allow seamless integration multiple room-temperature ferromagnetic with high-crystalline quality.
We report on the investigation of magnetic damping a 10 nm thin, poly-crystalline Co25Fe75 film grown by molecular beam epitaxy. Ferromagnetic resonance (FMR) measurements reveal low intrinsic αintFMR=(1.5±0.1)×10−3. In contrast, in patterned micrometer wide stripes, spin wave (SW) propagation experiments performed time resolved scanning magneto-optical Kerr microscopy yield attenuation lengths order 5–8 μm. From this quantity, we deduce an effective SW αeffSW, exp =(3.9±0.3)×10−3. For...
We report a systematic experimental study on the refraction and reflection of magnetostatic spin-waves at thickness step between two Permalloy films different thickness. The transmitted for transition from thick film to thin have higher wave vector compared incoming waves. Consequently, such systems may find use as passive wavelength transformers in magnonic networks. investigate spin-wave transmission behavior by studying influence external magnetic field, incident angle, ratio using...
We determine experimentally the spin structure of half-metallic Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following saturation, dominant states consist quasi-uniform configurations, where a strong influence from magnetocrystalline anisotropy is visible. Heating experiments show stability configuration domain walls in confined geometries up to 800 K. The switching temperature for transition transverse vortex ring found increase with width, an effect attributed...
A ratchet effect (the rectification of an ac injected current) which is purely magnetic in origin has been observed a superconducting-magnetic nanostructure hybrid. The hybrid consists superconducting Nb film contact with array nanoscale triangles, circular rings, or elliptical rings. arrays were placed into well-defined remanent states by application different field cycles. stray fields from these provide landscape influences the motion vortices. We examined both randomly varying landscapes...
The reversal process of thin film micron-scale Co/Cu/NiFe rhombic rings in an in-plane magnetic field is investigated by micromagnetic simulation and magnetoresistance measurements. Simulations show that the impingement reverse domains leads to formation multiple 360° domain walls ring during low-field cycling. Two types can be identified experimentally which are attributed presence or absence residual ring. path depends on history, affects population
In-plane and out-of-plane angular dependence of ferromagnetic resonance (FMR) magnetization measurements were performed on arrays 20, 40, 60 nm thick, 520 long, 250 wide elliptical Permalloy elements. Besides the main FMR “volume” mode resonance, a well-defined second was observed, which exhibits very strong dependence. This originates from localized regions where has component perpendicular to bias field volume magnetization. These nonuniform may be associated with canting at edges...
In a combined theoretical and experimental study, we investigate the critical current densities for vortex domain walls in magnetic nanowires. We systematically determine continuous motion of as function wire width different thicknesses find that density increases monotonously with decreasing width. Theoretically present mechanism predicts threshold based on wall transformations this leads to scaling ${j}_{c}\ensuremath{\propto}1/\text{width}$. The origin is found be dependence spin torque...
The evolution of the magnetization configurations in highly spin polarized La0.7Sr0.3MnO3 (LSMO) thin film elements (20–60 nm thickness) as a function external magnetic field and temperature is studied by direct imaging using x-ray circular dichroism photoemission electron microscopy. sample structuring done via pre-patterning process Cr mask layer. LSMO grows amorphous on layer for 20 thick but polycrystalline at larger thicknesses. Temperature dependent studies allow comparison properties...
We study the effect of magnetocrystalline anisotropy on magnetic configurations La0.7Sr0.3MnO3 bar and triangle elements using photoemission electron microscopy imaging. The dominant remanent state is a low energy flux-closure for both thin (15 nm) thick (50 elements. anisotropy, which competes with dipolar energy, causes strong modification spin configuration in elements, depending shape, size orientation structures. investigate switching processes observe triangular shaped displacement...
Strong superconducting pinning effects are observed from magnetic landscapes produced by arrays of circular rings with varying remanent states. The collective and the background Nb films is strongly enhanced stray field an array Ni magnetized to form “onion” (bidomain) On other hand, when same into vortex (flux-closed) states, or randomly magnetized, much smaller. greatest lattice motion along a direction in which there strong variation.