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

We present a systematic 2D spatial-coherence analysis of the soft-X-ray beamline P04 at PETRA III for various beamline configurations. The influence of two different beam-defining apertures on the spatial coherence properties of the beam is discussed and optimal conditions for coherence-based experiments are found. A significant degradation of the spatial coherence in the vertical direction has been measured and sources of this degradation are identified and discussed. The Fourier-analysis method, which gives fast and simple access to the 2D spatial coherence function of the X-ray beam, is used for the experiment. Here, we exploit the charge scattering of a disordered nanodot sample allowing the use of arbitrary X-ray photon energies with this method

Megahertz-rate ultrafast X-ray scattering and holographic imaging at the European XFEL

The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range

Observation of a Chirality-Induced Exchange-Bias Effect

Chiral magnetism that manifests in the existence of skyrmions or chiral domain walls offers an alternative way for creating anisotropies in magnetic materials that might have large potential for application in future spintronic devices. Here we show experimental evidence for an alternative type of in-plane exchange-bias effect present at room temperature that is created from a chiral 90 degrees domain wall at the interface of a ferrimagnetic-ferromagnetic Dy-Co/Ni-Fe bilayer system. The chiral interfacial domain wall forms due to the exchange coupling of Ni-Fe and Dy-Co at the interface and the presence of Dzyaloshinskii-Moriya interaction in the Dy-Co layer. As a consequence of the preferred chirality of the interfacial domain wall, the sign of the exchange-bias effect can be reversed by changing the perpendicular orientation of the Dy-Co magnetization. The chirality-created tunable exchange bias in Dy-Co/Ni-Fe is very robust against high in-plane magnetic fields (mu H-0 <= 6 T) and does not show any aging effects. Therefore, it overcomes the limitations of conventional exchange-bias systems

Observation of compact ferrimagnetic skyrmions in DyCo 3 film

Owing to the experimental discovery of magnetic skyrmions stabilized by the Dzyaloshinskii-Moriya and/or dipolar interactions in thin films, there is a recent upsurge of interest in magnetic skyrmions with antiferromagnetic spins in order to overcome the fundamental limitations inherent with skyrmions in ferromagnetic materials. Here, we report on the observation of compact ferrimagnetic skyrmions for the class of amorphous alloys consisting of 4f rare-earth and 3d transition-metal elements with perpendicular magnetic anisotropy, using a DyCo$_3$ film, that are identified by combining x-ray magnetic scattering, scanning transmission x-ray microscopy, and Hall transport technique. These skyrmions, with antiparallel aligned Dy and Co magnetic moments and a characteristic core radius of about 40~nm, are formed during the nucleation and annihilation of the magnetic maze-like domain pattern exhibiting a topological Hall effect contribution. Our findings provide a promising route for fundamental research in the field of ferrimagnetic/antiferromagnetic spintronics towards practical applications.Comment: 7 pages, 4 figure

Observation of compact ferrimagnetic skyrmions in DyCo₃ fim

Owing to the experimental discovery of magnetic skyrmions stabilized by the Dzyaloshinskii–Moriya and/or dipolar interactions in thin films, there is a recent upsurge of interest in magnetic skyrmions with antiferromagnetic spins in order to overcome the fundamental limitations inherent with skyrmions in ferromagnetic materials. Here, we report on the observation of compact ferrimagnetic skyrmions for the class of amorphous alloys consisting of 4f rare-earth and 3d transition-metal elements with perpendicular magnetic anisotropy, using a DyCo$_3$ film, that are identified by combining X-ray magnetic scattering, scanning transmission X-ray microscopy, and Hall transport technique. These skyrmions, with antiparallel aligned Dy and Co magnetic moments and a characteristic core radius of about 40 nm, are formed during the nucleation and annihilation of the magnetic maze-like domain pattern exhibiting a topological Hall effect contribution. Our findings provide a promising route for fundamental research in the field of ferrimagnetic/antiferromagnetic spintronics towards practical applications

Impact of Symmetry on Anisotropic Magnetoresistance in Textured Ferromagnetic Thin Films

We report on the magnetoresistance of textured films consisting of 3d-ferromagnetic layers sandwiched by Pt. While the conventional cos2φ behavior of the anisotropic magnetoresistance (AMR) is found when the magnetization M is varied in the film plane, cos2nθ contributions (2n≤6) exist for rotating M in the plane perpendicular to the current. This finding is explained by the symmetry-adapted modeling of AMR of textured films demonstrating that the cos2θ behavior cannot be used as a fingerprint for the presence of spin Hall magnetoresistance (SMR). Further, the interfacial MR contributions for Pt/Ni/Pt contradict the SMR behavior confirming the dominant role of AMR in all-metallic systems

Domain Walls in Bent Nanowires

The influence of geometric parameters on the magnetic fine structure of domain walls in bent nanowires is investigated. The domain pattern in the soft-magnetic Co39Fe54Si7 alloy is studied via scanning electron microscopy with polarization analysis and modeled via micromagnetic simulations. It is demonstrated that the bending angle affects details of the microstructure as well as the preponderant domain-wall type. A phenomenological model is developed that provides the global energy minimum of individual types of domain walls as a function of the geometric parameters of the wire. The results can be directly transferred to permalloy wires, as permalloy and Co39Fe54Si7 alloy have a comparable magnetostatic exchange length

Role of electronic excitation, relaxation and transport processes for X-ray induced ultrafast demagnetization within magnetic multilayer systems

We investigated the role of electronic excitation, relaxation and transport processes in X-ray induced ultrafast demagnetization of magnetic multilayer systems. In what follows, we report on the results obtained with the newly developed modeling tool, XSPIN, which enables nanoscopic description of electronic processes occurring in X-ray irradiated ferromagnetic materials. With this tool, we have studied the specific response of Co/Pt multilayer system irradiated by an ultrafast XUV pulse at the M-edge of Co (photon energy ~ 60 eV). It was previously studied experimentally at the FERMI free-electron-laser facility, using the magnetic small-angle X-ray scattering technique. The XSPIN simulations show that the magnetic scattering signal from cobalt decreases - on the femtosecond timescales considered - due to electronic excitation, relaxation and transport processes both in the cobalt and in the platinum layers. The signal decrease scales with the increasing fluence of incoming radiation, following the trend observed in the experimental data. Confirmation of the predominant role of electronic processes for X-ray induced demagnetization in the regime below the structural damage threshold, achieved with our theoretical study, is a step towards quantitative control and manipulation of X-ray induced magnetic processes on femtosecond timescales.Comment: 16 pages, 7 figure

Hard X-ray USAXS Fourier Transform Holography

We report on a Fourier transform holography study, employing hard X-ray energies at a 3rd generation storage ring. Nano-structures of various sizes and shapes have been measured in ultra small angle x-ray scattering configuration reaching a resolution in the holographic reconstructions of about 50 nm. Reliable holograms have been obtained with 6.9×106 incident photons. Our results provide an important step forward towards routine split-pulse Fourier transform holography measurements at FEL sources and 4th generation ultralow-emittance sources.