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This work presents a detailed analysis of the performance of X‐ray magnetic circular dichroism photoemission electron microscopy (XMCD‐PEEM) as a tool for vector reconstruction of magnetization. For this, 360° domain wall ring structures which form in a synthetic antiferromagnet are chosen as the model to conduct the quantitative analysis. An assessment is made of how the quality of the results is affected depending on the number of projections that are involved in the reconstruction process, as well as their angular distribution. For this a self‐consistent error metric is developed which allows an estimation of the optimum azimuthal rotation angular range and number of projections. This work thus proposes XMCD‐PEEM as a powerful tool for vector imaging of complex 3D magnetic structures. The performance of X‐ray magnetic circular dichroism photoemission electron microscopy for vector imaging of complex three‐dimensional magnetic textures is investigated.

The recent realizations of the quantum anomalous Hall effect (QAHE) in MnBi2Te4 and MnBi4Te7 benchmark the (MnBi2Te4)(Bi2Te3)n family as a promising hotbed for further QAHE improvements. The family owes its potential to its ferromagnetically (FM) ordered MnBi2Te4 septuple layers (SLs). However, the QAHE realization is complicated in MnBi2Te4 and MnBi4Te7 due to the substantial antiferromagnetic (AFM) coupling between the SLs. An FM state, advantageous for the QAHE, can be stabilized by interlacing the SLs with an increasing number n of Bi2Te3 quintuple layers (QLs). However, the mechanisms driving the FM state and the number of necessary QLs are not understood, and the surface magnetism remains obscure. Here, robust FM properties in MnBi6Te10 (n = 2) with Tc ≈ 12 K are demonstrated and their origin is established in the Mn/Bi intermixing phenomenon by a combined experimental and theoretical study. The measurements reveal a magnetically intact surface with a large magnetic moment, and with FM properties similar to the bulk. This investigation thus consolidates the MnBi6Te10 system as perspective for the QAHE at elevated temperatures. Stabilizing the quantum anomalous Hall effect in a magnetic topological insulator such as MnBi6Te10 is a promising route toward topological qubits, ultra‐low‐power electronics and spintronics. The most fundamental ingredient is ferromagnetic order; however, in pristine MnBi6Te10, the consecutive Mn layers interact antiferromagnetically. Here, it is demonstrated how Mn and Bi intermixing between their respective atomic positions may induce robust ferromagnetism.

Characterizing the chemistry and magnetism of magnetotactic bacteria (MTB) is an important aspect of understanding the biomineralization mechanism and function of the chains of magnetosomes (Fe₃O₄ nanoparticles) found in such species. Images and X-ray absorption spectra (XAS) of magnetosomes extracted from, and magnetosomes in, whole Magnetovibrio blakemorei strain MV-1 cells have been recorded using soft X-ray ptychography at the Fe 2p edge. A spatial resolution of 7 nm is demonstrated. Precursor-like and immature magnetosome phases in a whole MV-1 cell were visualized, and their Fe 2p spectra were measured. Based on these results, a model for the pathway of magnetosome biomineralization for MV-1 is proposed. Fe 2p X-ray magnetic circular dichroism (XMCD) spectra have been derived from ptychography image sequences recorded using left and right circular polarization. The shape of the XAS and XMCD signals in the ptychographic absorption spectra of both sample types is identical to the shape and signals measured with conventional bright-field scanning transmission X-ray microscope. A weaker and inverted XMCD signal was observed in the ptychographic phase spectra of the extracted magnetosomes. The XMCD ptychographic phase spectrum of the intracellular magnetosomes differed from the ptychographic phase spectrum of the extracted magnetosomes. These results demonstrate that spectro-ptychography offers a superior means of characterizing the chemical and magnetic properties of MTB at the individual magnetosome level.

Using x-ray magnetic nanotomography the internal magnetization structure within extended samples can be determined with high spatial resolution and element specificity, without the need for assumptions or prior knowledge of the magnetic properties of a sample. Here we present the details of a new algorithm for the reconstruction of a three-dimensional magnetization vector field, discussing both the mathematical description of the problem, and details of the gradient-based iterative reconstruction routine. To test the accuracy of the algorithm the method is demonstrated for a complex simulated magnetization configuration obtained from micromagnetic simulations. The reconstruction of the complex three-dimensional magnetic nanostructure, including the surroundings of magnetic singularities (or Bloch points), exhibits an excellent qualitative and quantitative agreement with the simulated magnetic structure. This method provides a robust route for the reconstruction of internal three-dimensional magnetization structures obtained from x-ray magnetic tomographic datasets, which can be acquired with either hard or soft x-rays, and can be applied to a wide variety of three-dimensional magnetic systems.

Unraveling the origin of ultrafast demagnetization in multisublattice ferromagnetic materials requires femtosecond x-ray techniques to trace the magnetic moment dynamics on individual elements, but this could not yet be achieved in the hard x-ray regime. We demonstrate here the first ultrafast demagnetization dynamics in the ferromagnetic heavy 5d-transition metal Pt using circularly-polarized hard x-rays at an x-ray free electron laser (XFEL). The decay time of laser-induced demagnetization of L1(0)-FePt is determined to be tau(Pt) = 0.61 +/- 0.04 ps using time-resolved x-ray magnetic circular dichroism at the Pt L-3 edge, whereas magneto-optical Kerr measurements indicate the decay time for the total magnetization as tau(total) < 0.1 ps. A transient magnetic state with a photomodulated ratio of the 3d and 5d magnetic moments is demonstrated for pump-probe delays larger than 1 ps. We explain this distinct photo-modulated transient magnetic state by the induced-moment behavior of the Pt atom and the x-ray probing depth. Our findings pave the way for the future use of XFELs to disentangle atomic spin dynamics contributions.

Unraveling the origin of ultrafast demagnetization in multisublattice ferromagnetic materials requires femtosecond x-ray techniques to trace the magnetic moment dynamics on individual elements, but this could not yet be achieved in the hard x-ray regime. We demonstrate here the first ultrafast demagnetization dynamics in the ferromagnetic heavy 5d-transition metal Pt using circularly-polarized hard x-rays at an x-ray free electron laser (XFEL). The decay time of laser-induced demagnetization of L10-FePt is determined to be τ Pt = 0.61 0.04 ps using time-resolved x-ray magnetic circular dichroism at the Pt L3 edge, whereas magneto-optical Kerr measurements indicate the decay time for the total magnetization as τ total < 0.1 ps . A transient magnetic state with a photo-modulated ratio of the 3d and 5d magnetic moments is demonstrated for pump-probe delays larger than 1 ps. We explain this distinct photo-modulated transient magnetic state by the induced-moment behavior of the Pt atom and the x-ray probing depth. Our findings pave the way for the future use of XFELs to disentangle atomic spin dynamics contributions.

Photoemission electron microscopy (PEEM) is a powerful technique for surface characterization that provides detailed information on the chemical and structural properties of materials at the nanoscale. In this study, the potential is explored using a machine learning algorithm called self‐organizing map with a relational perspective map (SOM‐RPM) for visualizing and analyzing complex PEEM‐generated datasets. The application of SOM‐RPM is demonstrated using synchrotron‐based X‐ray magnetic circular dichroism (XMCD)‐PEEM data acquired from a pyrrhotite sample. Traditional visualization approaches for XMCD‐PEEM data may not fully capture the complexity of the sample, especially in the case of heterogeneous materials. By applying SOM‐RPM to the XMCD‐PEEM data, a colored topographic map is created that represents the spectral similarities and dissimilarities among the pixels. This approach allows for a more intuitive and easily interpretable representation of the data without the need of data binning or spectral smoothing. The results of the SOM‐RPM analysis are compared to the conventional visualization approach, highlighting the advantages of SOM‐RPM in revealing features that are not readily observable in the conventional method. This study suggests that the SOM‐RPM approach can be used complimentarily for other PEEM‐based measurements, such as core level and valence band X‐ray photoelectron spectroscopy. This study explores the use of a machine learning algorithm, self‐organizing map and relational perspective mapping (SOM‐RPM), to visualize complex photoemission electron microscopy (PEEM)‐generated datasets. Applying SOM‐RPM to X‐ray magnetic circular dichroism, PEEM data creates a colored topographic map, representing spectral similarities and dissimilarities. Compared to traditional approaches, SOM‐RPM reveals previously unnoticed features, making it suitable for heterogeneous materials and other PEEM‐based measurements.

MAXPEEM, a dedicated photoemission electron microscopy beamline at MAX IV Laboratory, houses a state‐of‐the‐art aberration‐corrected spectroscopic photoemission and low‐energy electron microscope (AC‐SPELEEM). This powerful instrument offers a wide range of complementary techniques providing structural, chemical and magnetic sensitivities with a single‐digit nanometre spatial resolution. The beamline can deliver a high photon flux of ≥1015 photons s−1 (0.1% bandwidth)−1 in the range 30–1200 eV with full control of the polarization from an elliptically polarized undulator. The microscope has several features which make it unique from similar instruments. The X‐rays from the synchrotron pass through the first beam separator and impinge the surface at normal incidence. The microscope is equipped with an energy analyzer and an aberration corrector which improves both the resolution and the transmission compared with standard microscopes. A new fiber‐coupled CMOS camera features an improved modulation transfer function, dynamic range and signal‐to‐noise ratio compared with the traditional MCP‐CCD detection system. The design and performance of a new dedicated spectromicroscopy beamline at the Swedish national synchrotron (MAX IV) is presented.

This investigation reports on anisotropy in the magnetic interaction, lattice-orbital coupling and degree of phonon softening in single crystal Ni 3 TeO 6 (NTO) using temperature- and polarization-dependent X-ray absorption spectroscopic techniques. The magnetic field-cooled and zero-field-cooled measurements and temperature-dependent Ni L 3,2 -edge X-ray magnetic circular dichroism spectra of NTO reveal a weak Ni-Ni ferromagnetic interaction close to ~60 K ( T SO : temperature of the onset of spin ordering) with a net alignment of Ni spins (the uncompensated components of the Ni moments) along the crystallographic c -axis, which is absent from the ab -plane. Below the Néel temperature, T N ~ 52 K, NTO is stable in the antiferromagnetic state with its spin axis parallel to the c -axis. The Ni L 3,2 -edge X-ray linear dichroism results indicate that above T SO , the Ni 3 d e g electrons preferentially occupy the out-of-plane 3 d 3z 2 −r 2 orbitals and switch to the in-plane 3 d x 2 −y 2 orbitals below T SO . The inherent distortion of the NiO 6 octahedra and anisotropic nearest-neighbor Ni-O bond lengths between the c -axis and the ab -plane of NTO, followed by anomalous Debye-Waller factors and orbital-lattice in conjunction with spin-phonon couplings, stabilize the occupied out-of-plane (3 d 3z 2 −r 2 ) and in-plane (3 d x 2 −y 2 ) Ni e g orbitals above and below T SO , respectively.

Magnetic vector tomography allows for visualizing the 3D magnetization vector of magnetic nanostructures and multilayers with nanometric resolution. In this work, we present MARTApp (Magnetic Analysis and Reconstruction of Tomographies Application), a software designed to analyze the images obtained from a full‐field or scanning transmission X‐ray microscope and reconstruct the 3D magnetization of the sample. Here, its workflow and main features are described. Moreover, a synthetic test sample consisting of a hopfion is used to exemplify the workflow from raw images to the final 3D magnetization reconstruction. MARTApp is an open‐source software for magnetic vector reconstruction of the data acquired from magnetic transmission X‐ray microscopy. It automates the tasks of image normalization, alignment, computation of magnetic signal and the reconstruction of quasi‐2D and ‐3D systems. Following the developed procedure, the magnetization of a simulated 3D magnetic texture has been recovered.