The ferroelectric domain structure of a freestanding BiFeO3 film was visualized by ptychographic dichroic imaging with linearly polarized x-rays at the O K-edge around 530 eV. The dichroic contrast is maximized at the energy of the hybridization of the O 2p state and the Fe 3d orbitals, which is split by the octahedral crystal field of the perovskite structure. The microscopy images thus obtained complement the ptychographic imaging of the antiferromagnetic contribution at the Fe L3-edge. The approach can be extended to the separation of different ferroic contributions in other multiferroic oxides. Published by the American Physical Society 2025

Artificially aligned or positioned functional materials are essential building blocks for modern devices and nanoelectronics. Since the emergence of 2D materials, the vertical stacking/integration of exotic materials has garnered increasing attention. However, controlling homostructures, e.g. identical materials conjoined with varying crystalline orientations, magnetism, or strain states, along the lateral direction remains challenging. Leveraging on the freestanding thin film growth techniques, the concept of twisted lateral homostructures has been introduced, enabling precise control over the lateral alignment of crystalline directions. Here, using La0.7Sr0.3MnO3, a classic strongly correlated material, the precise manipulation of epitaxial strain alongside the homojunction is demonstrated. This leads to a precisely controllable lateral homostructure composed of polymorphic ferromagnetic and antiferromagnetic La0.7Sr0.3MnO3 regions. It is further identified that the interactions between the ferromagnetic and antiferromagnetic regions of La0.7Sr0.3MnO3 lead to unconventional ultrafast spin dynamics and magnetotransport behavior. The results provide a promising platform for developing novel emergent phenomena and functionalities in the twisted lateral homostructures.

Time-resolved pump-probe soft x-ray ptychography and scanning transmission x-ray microscopy were employed to study the magnetic domain-wall dynamics in microstructures of permalloy (Ni81Fe19; Py) with a weak growth-induced perpendicular magnetic anisotropy. The x-ray magnetic circular dichroism images of a micrometer-sized Py square (160 nm thickness) and an elliptical disk (80 nm thickness) show flux-closure patterns with domain walls that fall into alternating out-of-plane (OOP) magnetization states precipitated by the perpendicular anisotropy, which is a precursor of the nucleation of stripe domains at higher thicknesses. An oscillating magnetic field at frequencies from tens of MHz to GHz and up to 4 mT magnitude excited dynamic modes in the domain walls along with the vortex core gyration. The domain-wall dynamics include the translation of inversion points of the OOP magnetization and nucleation of one-dimensional spin waves.

Neutron imaging was employed to track the uptake of Gd ^3+ ions by the sub 2 nm micropores of charged activated carbon cloth electrodes from an aqueous Gd(NO _3 ) _3 solution. The transmitted neutron intensity evinces the persistent presence of Gd ^3+ in the micropores during the discharge cycle, which is caused by the adsorption of oppositely charged ions. The charge efficiency of the activated carbon cloth system was determined by direct comparison with the imaged Gd ^3+ concentration changes, with which the influence of ion swapping and resistive losses on capacitive deionization cells can be ascertained.

Antiferromagnets hosting real-space topological textures are promising platforms to model fundamental ultrafast phenomena and explore spintronics. However, they have only been epitaxially fabricated on specific symmetry-matched substrates, thereby preserving their intrinsic magneto-crystalline order. This curtails their integration with dissimilar supports, restricting the scope of fundamental and applied investigations. Here we circumvent this limitation by designing detachable crystalline antiferromagnetic nanomembranes of α-Fe 2 O 3 . First, we show—via transmission-based antiferromagnetic vector mapping—that flat nanomembranes host a spin-reorientation transition and rich topological phenomenology. Second, we exploit their extreme flexibility to demonstrate the reconfiguration of antiferromagnetic states across three-dimensional membrane folds resulting from flexure-induced strains. Finally, we combine these developments using a controlled manipulator to realize the strain-driven non-thermal generation of topological textures at room temperature. The integration of such free-standing antiferromagnetic layers with flat/curved nanostructures could enable spin texture designs via magnetoelastic/geometric effects in the quasi-static and dynamical regimes, opening new explorations into curvilinear antiferromagnetism and unconventional computing.

Hybrid pixel detectors have become indispensable at synchrotron and X-ray free-electron laser facilities thanks to their large dynamic range, high frame rate, low noise, and large area. However, at energies below 3 keV, the detector performance is often limited because of the poor quantum efficiency of the sensor and the difficulty in achieving single-photon resolution due to the low signal-to-noise ratio. In this paper, we address the quantum efficiency of silicon sensors by refining the design of the entrance window, mainly by passivating the silicon surface and optimizing the dopant profile of the n+ region. We present the measurement of the quantum efficiency in the soft X-ray energy range for silicon sensors with several process variations in the fabrication of planar sensors with thin entrance windows. The quantum efficiency for 250 eV photons is increased from almost 0.5% for a standard sensor to up to 62% as a consequence of these developments, comparable to the quantum efficiency of backside-illuminated scientific CMOS sensors. Finally, we discuss the influence of the various process parameters on quantum efficiency and present a strategy for further improvement.

Soft X-ray ptychography was employed to simultaneously image the ferroelectric and antiferromagnetic domains in an 80 nm thick freestanding multiferroic BiFeO_3. The antiferromagnetic spin cycloid was resolved by reconstructing the resonant elastic X-ray scattering and visualised together with mosaic-like ferroelectric domains in a linear dichroic contrast image at the Fe L_3 edge. The measurements reveal a near perfect coupling between the magnetic and ferroelectric ordering by which the propagation direction of the spin cycloid is locked orthogonally to the ferroelectric polarisation. The results provide a direct visualisation of the strong magnetoelectric coupling in BiFeO_3 and of its fine multiferroic domain structure, emphasising the potential of high resolution ptychographic imaging in opening new possibilities for the study of multiferroics and non-collinear magnetic materials with soft X-rays.

AbstractA brief introduction to the main concepts that underpin the interaction of magnetic fields with fluids is given. The effect of the main magnetic force densities, the Kelvin force in a magnetic field gradient and the Lorentz force in magnetohydrodynamics is discussed. The focus lies on incompressible fluids that are enclosed by solid walls such as are prevalent in microfluidic systems. These are only influenced by rotational body forces.

Experiments at synchrotron radiation sources and X-ray Free-Electron Lasers in the soft X-ray energy range (250 eV–2 keV) stand to benefit from the adaptation of the hybrid silicon detector technology for low energy photons. Inverse Low Gain Avalanche Diode (iLGAD) sensors provide an internal gain, enhancing the signal-to-noise ratio and allowing single photon detection below 1 keV using hybrid detectors. In addition, an optimization of the entrance window of these sensors enhances their quantum efficiency (QE). In this work, the QE and the gain of a batch of different iLGAD diodes with optimized entrance windows were characterized using soft X-rays at the Surface/Interface:Microscopy beamline of the Swiss Light Source synchrotron. Above 250 eV, the QE is larger than 55% for all sensor variations, while the charge collection efficiency is close to 100%. The average gain depends on the gain layer design of the iLGADs and increases with photon energy. A fitting procedure is introduced to extract the multiplication factor as a function of the absorption depth of X-ray photons inside the sensors. In particular, the multiplication factors for electron- and hole-triggered avalanches are estimated, corresponding to photon absorption beyond or before the gain layer, respectively.

Atomistic spin dynamics (ASD) simulations of ultrafast demagnetization in ferromagnetic iron and cobalt. The ASD simulations here are energy-conserving, which means that energy flow into and out of the spin system is considered. The dataset contains simulations at four different pump laser fluences for iron and six different fluences for cobalt. The excitation was assumed to be homogeneous throughout the simulated volume. The heat capacities and electron-phonon coupling parameters which were used in the ASD simulations are provided in the folder "heat capacities and G_ep". More information is available here:- https://arxiv.org/abs/2110.00525- Zahn et al. Phys. Rev. Research 3, 023032 (2021)https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.023032

Ultrafast magnetization dynamics are governed by energy flow between electronic, magnetic, and lattice degrees of freedom. A quantitative understanding of these dynamics must be based on a model that agrees with experimental results for all three subsystems. However, ultrafast dynamics of the lattice remain largely unexplored experimentally. Here we combine femtosecond electron diffraction experiments of the lattice dynamics with energy-conserving atomistic spin dynamics (ASD) simulations and ab initio calculations to study the intrinsic energy flow in the $3d$ ferromagnets cobalt (Co) and iron (Fe). The simulations yield a good description of experimental data, in particular an excellent description of our experimental results for the lattice dynamics. We find that the lattice dynamics are influenced significantly by the magnetization dynamics due to the energy cost of demagnetization. Our results highlight the role of the spin system as the dominant heat sink in the first hundreds of femtoseconds. Together with previous findings for nickel [Zahn et al., Phys. Rev. Research 3, 023032 (2021)], our work demonstrates that energy-conserving ASD simulations provide a general and consistent description of the laser-induced dynamics in all three elemental $3d$ ferromagnets.

An overview of the effect of a magnetic field gradient on fluids with linear magnetic susceptibilities is given. It is shown that two commonly encountered expressions, the magnetic field gradient force and the concentration gradient force for paramagnetic species in solution are equivalent for incompressible fluids. The magnetic field gradient and concentration gradient forces are approximations of the Kelvin force and Korteweg-Helmholtz force densities, respectively. The criterion for the appearance of magnetically induced convection is derived. Experimental work in which magnetically induced convection plays a role is reviewed.

Tim A. Butcher, ∗ Lucy Prendeville, Aran Rafferty, Pavel Trtik, Pierre Boillat, 4 and J. M. D. Coey School of Physics and CRANN, Trinity College, Dublin 2, Ireland AMBER Centre and School of Chemistry, Trinity College, Dublin 2, Ireland Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen, Switzerland Electrochemistry Laboratory, Paul Scherrer Institut, CH-5232 Villigen, Switzerland (Dated: July 7, 2021)

The electrosorption of Gd3+ ions from an aqueous 70 mM Gd(NO3)3 solution in monolithic carbon aerogel electrodes was recorded by dynamic neutron imaging. The aerogels have a bimodal pore size distribution consisting of macropores and mesopores centered at 115 and 15 nm, respectively. After the uptake of Gd3+ ions by the negatively charged surface of the porous structure, an inhomogeneous magnetic field was applied to the system of discharging electrodes. This led to a convective flow and confinement of Gd(NO3)3 solution in the magnetic field gradient. Thus, a way to desalt and capture paramagnetic ions from an initially homogeneous solution is established.

The electrosorption of Gd$^{3+}$ ions from aqueous 70$\,$mM Gd(NO$_3$)$_3$ solution in monolithic carbon aerogel electrodes was recorded by dynamic neutron imaging. The aerogels have a bimodal pore size distribution consisting of macropores centred at 115$\,$nm and mesopores centred at 15$\,$nm. After the uptake of Gd$^{3+}$ ions by the negatively charged surface of the porous structure, an inhomogeneous magnetic field was applied to the system of discharging electrodes. This led to a convective flow and confinement of Gd(NO$_3$)$_3$ solution in the magnetic field gradient. Thus, a way to desalt and capture paramagnetic ions from an initially homogeneous solution is established.

The ultrafast dynamics of magnetic order in a ferromagnet are governed by the interplay between electronic, magnetic, and lattice degrees of freedom. In order to obtain a microscopic understanding of ultrafast demagnetization, information on the response of all three subsystems is required. A consistent description of demagnetization and microscopic energy flow, however, is still missing. Here, we combine a femtosecond electron diffraction study of the ultrafast lattice response of nickel to laser excitation with ab initio calculations of the electron-phonon interaction and energy-conserving atomistic spin dynamics simulations. Our model is in agreement with the observed lattice dynamics and previously reported electron and magnetization dynamics. Our approach reveals that the spin system is the dominating heat sink in the initial few hundred femtoseconds and implies a transient nonthermal state of the spins. Our results provide a clear picture of the microscopic energy flow between electronic, magnetic, and lattice degrees of freedom on ultrafast timescales and constitute a foundation for theoretical descriptions of demagnetization that are consistent with the dynamics of all three subsystems.

The method of neutron imaging was adopted to map the concentration evolution of aqueous paramagnetic Gd(NO3)(3) solutions. Magnetic manipulation of the paramagnetic liquid within a miscible nonmagnetic liquid is possible by countering density-difference driven convection. The formation of salt fingers caused by double-diffusive convection in a liquid-liquid system of Gd(NO3)(3) and Y(NO3)(3) solutions can be prevented by the magnetic field gradient force.

The noncentrosymmetric superconductor alpha-PdBi is a candidate material for the realization of topological superconductivity. Here, we present a detailed de Haas-van Alphen (dHvA) study together with band-structure calculations within the framework of density functional theory. The rich dHvA spectra are a manifestation of the 13 bands that cross the Fermi energy E-F. We find excellent agreement between calculated and experimentally observed dHvA frequencies with moderately enhanced effective masses. One of the bands crossing E-F, the so-called alpha band, exhibits topological character with Weyl nodes lying 43 meV below E-F.

The transversal magnetoresistance associated with the semimetal TaAs2 shows a parabolic field dependence that rises unrestrictedly to 2800 at 14 T and 1.8 K. Here, we report the results of a comprehensive quantum-oscillation study. Angular-dependent de Haas-van Alphen (dHvA) data were obtained with the method of cantilever-torque magnetometry. These were compared with the results of density-functional theory calculations, which predict a Fermi surface with two kinds of electron pockets, as well as two types of hole pockets. Only the electron pockets could be experimentally verified, whereas no evidence for the hole pockets is present in the measured dHvA frequencies.