High-resolution X-ray ptychography for magnetic imaging

The resolution in standard X-ray microscopes is limited by the focusing element, e.g. Fresnel Zone Plates (FZP), and stays in the range of 20 nm for highly efficient plates. Diffraction imaging techniques with the use of coherent X-ray radiation potentially can achieve wavelength limited resolution solving so-called “phase problem”. Ptychography is the combination of diffraction imaging and scanning transmission microscopy that provides images of extended sample areas utilizing iterative reconstruction algorithm. The main focus of this thesis is the realization of ptychographic imaging on the samples with different scattering power, as well as the investigation and improvement of the microscopic potential of this method in detailed comparison with conventional STXM imaging. The technique is applied to sub-100 nm sized magnetic structures of the current scientific interest, i.e. domain walls, vortices and skyrmions

Skyrmion Hall Effect Revealed by Direct Time-Resolved X-Ray Microscopy

Magnetic skyrmions are highly promising candidates for future spintronic applications such as skyrmion racetrack memories and logic devices. They exhibit exotic and complex dynamics governed by topology and are less influenced by defects, such as edge roughness, than conventionally used domain walls. In particular, their finite topological charge leads to a predicted "skyrmion Hall effect", in which current-driven skyrmions acquire a transverse velocity component analogous to charged particles in the conventional Hall effect. Here, we present nanoscale pump-probe imaging that for the first time reveals the real-time dynamics of skyrmions driven by current-induced spin orbit torque (SOT). We find that skyrmions move at a well-defined angle {\Theta}_{SH} that can exceed 30{\deg} with respect to the current flow, but in contrast to theoretical expectations, {\Theta}_{SH} increases linearly with velocity up to at least 100 m/s. We explain our observation based on internal mode excitations in combination with a field-like SOT, showing that one must go beyond the usual rigid skyrmion description to unravel the dynamics.Comment: pdf document arxiv_v1.1. 24 pages (incl. 9 figures and supplementary information

Socio-Geographical Concept of Labor Market Monitoring and Regional Employment Policy Formation

The necessity of socio-geographical concept elaboration and implementation for labor market monitoring and regional employment policy formation is grounded from the socio-geographical point of view. It has been established that: 1) the versatility and complex nature of the labor market development specificated by natural and socio-economic factors of important geographical content has determined its socio-geographical essence; 2) the development of the concept requires different approaches, principles and research methods, including socio-geographical, taking into account various labor market factors; 3)the concept should take into account the influence of the laws of the production and human settlement territorial organisation, as well as the level of development and structure of the region's economy; 4)the concept should take into account the peculiarities of the labor market formation and development in the economic system agricultural sector as well as the impact of current risks and challenges on the social and labor sphere of public life; 5) the implementation of such a concept has to provide the balancing of labor supply and demand within the country and its regions; 6)regional employment policy should be aimed at rational use of the territory labor potential

Ptychographic imaging and micromagnetic modeling of thermal melting of nanoscale magnetic domains in antidot lattices

Antidot lattices are potential candidates to act as bit patterned media for data storage as they are able to trap nanoscale magnetic domains between two adjacent holes. Here, we demonstrate the combination of micromagnetic modeling and x-ray microscopy. Detailed simulation of these systems can only be achieved by micromagnetic modeling that takes thermal effects into account. For this purpose, a Landau–Lifshitz–Bloch approach is used here. The calculated melting of magnetic domains within the antidot lattice is reproduced experimentally by x-ray microscopy. Furthermore, we compare conventional scanning transmission x-ray microscopy with resolution enhanced ptychography. Hence, we achieve a resolution of 13 nm. The results demonstrate that ptychographic imaging can also recover magnetic contrast in the presence of a strong topological variation and is generally applicable toward magnetic samples requiring ultimate resolution.publishe

Chemical Stability of FeOOH at High Pressure and Temperature, and Oxygen Recycling in Early Earth History

Goethite, $α$-FeOOH, is a major phase among oxidized iron species, commonly called rust. We studied the behavior of iron (III) oxyhydroxide up to 81 GPa and 2100 K using in situ synchrotron single-crystal X-ray diffraction. At high pressure-temperature conditions FeOOH decomposes forming oxygen-rich fluid and different mixed valence iron oxides (previously known phases of Fe$_2$O$_3$, Fe$_3$O$_4$, Fe$_5$O$_7$, and novel Fe$_7$O$_{10}$ and Fe$_{6.32}$O$_9$). Rust is known to form as a byproduct of anoxygenic prokaryote metabolism that took place massively from about 3.8 billion years (Ga) ago until the Great Oxidation Event (GOE) ∼2.2 Ga ago. Rust was buried on the ocean floor and was transported into the mantle as a consequence of plate tectonics (started ∼2.8 Ga ago). Our results suggest that recycling of rust in Earth's mantle contributes to redox conditions of the early Earth and formation of oxygen-rich atmosphere

Front Cover: Chemical Stability of FeOOH at High Pressure and Temperature, and Oxygen Recycling in Early Earth History (Eur. J. Inorg. Chem. 30/2021)

The Front Cover shows a possible deep oxygen cycle in early Earth. FeOOH (“rust”), produced by anoxygenic photosynthesis and accumulated on the ocean floor, was transferred to the lower mantle by subducting slabs. At high pressures and temperatures, FeOOH decomposes into a mixture of complex iron oxides, water, and oxygen. Oxidizing fluids rising to the Earth′s surface could then possibly contribute to (or even be one of the main causes of) the Great Oxidation Event about 2.5 billion years ago. Image credits: Egor Koemets, Timofey Fedotenko, Leonid Dubrovinsky (Bayreuth University). More information can be found in the Full Paper by E. Koemets and co-workers

Reprogrammability and Scalability of Magnonic Fibonacci Quasicrystals

Magnonic quasicrystals can be used to manipulate spin waves, offering possibilities beyond those of periodic magnonic crystals. The authors investigate one-dimensional magnonic Fibonacci quasicrystals and demonstrate the existence of collective spin waves over a broad range of wave vectors. The spin-wave spectra here are tunable by changing magnetic field amplitude (for continuous band-structure adjustment), magnetization configuration (for reprogrammability), or the dimensions of the elements (for scalability). Beyond being fundamentally interesting, these properties show that magnonic quasicrystals are promising for tomorrow's spintronic, microwave, and magnonic technologies

High-resolution ptychographic imaging at a seeded free-electron laser source using OAM beams

International audienceElectromagnetic waves possessing orbital angular momentum (OAM) are powerful tools for applications in optical communications, quantum technologies, and optical tweezers. Recently, they have attracted growing interest since they can be harnessed to detect peculiar helical dichroic effects in chiral molecular media and in magnetic nanostructures. In this work, we perform single-shot per position ptychography on a nanostructured object at a seeded free-electron laser, using extreme ultraviolet OAM beams of different topological charge orders ℓ generated with spiral zone plates. By controlling ℓ, we demonstrate how the structural features of OAM beam profiles determine an improvement of about 30% in image resolution with respect to conventional Gaussian beam illumination. This result extends the capabilities of coherent diffraction imaging techniques, and paves the way for achieving time-resolved high-resolution (below 100 nm) microscopy on large area samples