arXiv subjects

Burkhard Kaulich

Publications and source records attributed to Burkhard Kaulich.

4 recordsLinked to original sources

arXiv2026

Physics-informed X-ray tomography of magnetization and material parameters

Three-dimensional spin textures are stabilized by microscopic interactions within their host materials. X-ray vector tomography can image these nanoscale structures, but weak magnetic contrast and a limited range of viewing angles often leave parts of the magnetization poorly determined. Here we show that a reconstruction constrained by the micromagnetic energy recovers the three-dimensional magnetization from such data and gains sensitivity to the underlying material interactions. Applied to the chiral magnet Co$_8$Zn$_9$Mn$_3$, the method resolves the three-dimensional helical texture even from a small fraction of the dual-axis projections typically required for a successful tomographic reconstruction, or from a single tilt axis alone. By testing which ratio of exchange to Dzyaloshinskii-Moriya interaction in the reconstruction best reproduces the measured projections, we obtain a value for the sample that differs by about 10 % from the literature value derived from the helical winding period. Taken together, our findings suggest a way to reduce the time needed for vector tomography and to extend it to determining fundamental magnetic interactions in a material.

cond-mat.mes-hall↗

arXiv2026

Dipole chains of Bloch point singularities revealed by X-ray magnetic tomography

Bloch point singularities play an important role in magnetic systems, mediating changes in topology in three dimensional configurations. However, until now they have only been observed as isolated objects or as part of individual topological textures. Here we present the experimental observation of a 1D dipole chain of Bloch points in an anisotropic chiral magnet using soft X-ray magnetic vector tomography. We identify that the chain of Bloch point singularities lies along a boundary between regions of opposite chirality and that neighbouring Bloch and anti-Bloch points are stable at separations down to 60 nm. The stability of the Bloch points is determined to be closely related to the surrounding topology of the magnetisation configuration and a threshold separation for the spontaneous annihilation of Bloch point-anti-Bloch point pairs within chiral domain walls is identified to be approximately 90 nm in distance. This observation of a chain of Bloch points and the insight into their stability, offers a route to explore the correlative behaviour of such topological point defects. The behaviour and control of such point defects is of relevance for the control of 3D magnetisation configurations, and provides a new route towards the creation of correlated configurations of singularities in a magnetic system.

cond-mat.mes-hall↗

arXiv2025

Nanoscale Mapping of Magnetic Orientations with Complex X-ray Magnetic Linear Dichroism

Compensated magnets are of increasing interest for both fundamental research and applications, with their net-zero magnetization leading to ultrafast dynamics and robust order. To understand and control this order, nanoscale mapping of local domain structures is necessary. One of the main routes to mapping antiferromagnetic order is X-ray magnetic linear dichroism (XMLD), which probes the local orientation of the Néel vector. However, XMLD imaging typically suffers from weak contrast and has mainly been limited to surface-sensitive techniques. Here, we harness coherent diffractive imaging to map the complex XMLD spectroscopically, and identify the phase linear dichroism as a high-contrast, high-resolution mechanism for imaging magnetic order. By applying X-ray spectroptychography to a model sample, we retrieve the full complex XMLD spectrum. Combining this with hierarchical clustering, we resolve the spatial distribution of probed domains by their distinct spectral signatures, providing a robust method for analyzing magnetic configurations with weak signals. Our results show that phase contrast is significantly stronger than the corresponding absorption contrast, offering higher spatial-resolution magnetic imaging. This approach establishes a reliable, element- and orbital-sensitive tool for studying compensated magnets.

cond-mat.mes-hall↗

arXiv2023

Soft X-ray phase nano-microscopy of micrometre-thick magnets

Imaging of nanoscale magnetic textures within extended material systems is of critical importance both to fundamental research and technological applications. Whilst high resolution magnetic imaging of thin nanoscale samples is well-established with electron and soft X-ray microscopy, the extension to micrometer-thick systems with hard X-rays currently limits high resolution imaging to rare-earth magnets. Here we overcome this limitation by establishing soft X-ray magnetic imaging of micrometer-thick systems using the pre-edge phase X-ray Magnetic Circular Dichroism signal, thus making possible the study of a wide range of magnetic materials. By performing dichroic spectro-ptychography, we demonstrate high spatial resolution imaging of magnetic samples up to 1.7 μm thick, an order of magnitude higher than conventionally possible with absorption-based techniques. This new regime of magnetic imaging makes possible the study of extended non rare-earth systems that have until now been inaccessible, from magnetic textures for future spintronic applications to non-rare-earth permanent magnets.

cond-mat.mes-hall↗