arXiv subjects

Elisabeth Müller

Publications and source records attributed to Elisabeth Müller.

6 recordsLinked to original sources

arXiv2026

In-situ Straining of Epitaxial Freestanding Ferroic Films by a MEMS Device

Mechanical strain can be used to control physical properties in materials. The experimental investigation of strain-induced effects at the nanoscale is of importance not only for its fundamental aspects, but also for the development of device applications. Transmission X-ray microscopy is a particularly well-suited technique for nanoscale imaging of magnetic materials, but its compatibility with in-situ mechanical straining of samples is limited. In this work, we present a setup for applying tailored in-situ mechanical strains to freestanding thin films by means of a micro electromechanical system (MEMS) actuator. We then present a proof-of-concept experiment in which a freestanding 80 nm thick (001) BiFeO3 multiferroic thin film is strained with the MEMS device, allowing us to control the coupled ferroelectric/spin cycloidal configuration.

cond-mat.mes-hall↗

arXiv2026

Sub-Pixel Electron Beam Alignment for Machine Learning Characterization of Hybrid Pixel Detectors

Due to their radiation hardness, kilohertz frame rates, and high dynamic range, hybrid pixel detectors have recently expanded their application range to electron diffraction and recently also electron imaging. However, these detectors typically have pixel sizes about ten times larger than those of direct electron detectors commonly used for imaging and more prominent electron multiple scattering effects. To overcome these limitations, machine learning approaches can be utilized to reconstruct the electron entrance point and achieve super-resolution. As this process is inherently stochastic, and machine learning relies on suitable training data, high-quality, representative training data are essential for developing models that achieve the best possible resolution. In this work, we present two novel experimental methods for generating such training data. The first method employs precise microscope alignment to scan the detector plane using a finely focused electron beam of 2 μm diameter, enabling controlled sub-pixel mapping. The second method utilizes specially designed aperture masks with sub-pixel-sized holes to accurately localize electron entry points. We developed and validated two experimental strategies for collecting training data at acceleration voltages of 60, 80, 120, and 200 keV, which enable sub-pixel labeling for hybrid pixel detectors. Notably, our methodology is broadly applicable to a wide range of hybrid pixel detectors.

physics.ins-det↗

arXiv2026

Generating unconventional spin-orbit torques with patterned phase gradients in tungsten thin films

A key aim in spintronics is to achieve current-induced magnetization switching via spin-orbit torques without external magnetic fields. For this, the focus of recent work has been on introducing controlled lateral gradients across ferromagnet/heavy-metal devices, giving variations in thickness, composition, or interface quality. However, the small gradients achievable with common growth techniques limit both the impact of this approach and understanding of the underlying physical mechanisms. Here, spin-orbit torques are patterned on a mesoscopic length scale in tungsten thin films using direct-write laser annealing. Through transmission electron microscopy, resistivity, and second harmonic measurements, the continuous transformation of the crystalline phase of W films from the highly spin-orbit coupled, high resistivity $β$ phase to the minimally spin-orbit coupled, low resistivity $α$ phase is tracked with increasing laser fluence. Gradients with different steepness are patterned in the tungsten phase to create spin-orbit torque channels and, when interfaced with CoFeB, tungsten wires with a sufficiently strong gradient can switch the magnetization without an applied magnetic field. Therefore, exploiting the unique microstructure of mixed-phase W allows precise control of the local electronic current density and direction, as well as local spin-orbit torque efficiency, providing a new avenue for the design of efficient spintronic devices.

cond-mat.mes-hall↗

arXiv2024

Emergence of interfacial magnetism in strongly-correlated nickelate-titanate superlattices

Strongly-correlated transition-metal oxides are widely known for their various exotic phenomena. This is exemplified by rare-earth nickelates such as LaNiO$_{3}$, which possess intimate interconnections between their electronic, spin, and lattice degrees of freedom. Their properties can be further enhanced by pairing them in hybrid heterostructures, which can lead to hidden phases and emergent phenomena. An important example is the LaNiO$_{3}$/LaTiO$_{3}$ superlattice, where an interlayer electron transfer has been observed from LaTiO$_{3}$ into LaNiO$_{3}$ leading to a high-spin state. However, macroscopic emergence of magnetic order associated with this high-spin state has so far not been observed. Here, by using muon spin rotation, x-ray absorption, and resonant inelastic x-ray scattering, we present direct evidence of an emergent antiferromagnetic order with high magnon energy and exchange interactions at the LaNiO$_{3}$/LaTiO$_{3}$ interface. As the magnetism is purely interfacial, a single LaNiO$_{3}$/LaTiO$_{3}$ interface can essentially behave as an atomically thin strongly-correlated quasi-two-dimensional antiferromagnet, potentially allowing its technological utilisation in advanced spintronic devices. Furthermore, its strong quasi-two-dimensional magnetic correlations, orbitally-polarized planar ligand holes, and layered superlattice design make its electronic, magnetic, and lattice configurations resemble the precursor states of superconducting cuprates and nickelates, but with an $S \rightarrow 1$ spin state instead.

cond-mat.str-el↗

arXiv2024

Calibrating coordinate system alignment in a scanning transmission electron microscope using a digital twin

In four-dimensional scanning transmission electron microscopy (4D STEM) a focused beam is scanned over a specimen and a diffraction pattern is recorded at each position using a pixelated detector. During the experiment, it must be ensured that the scan coordinate system of the beam is correctly calibrated relative to the detector coordinate system. Various simplified and approximate models are used implicitly and explicitly for understanding and analyzing the recorded data, requiring translation between the physical reality of the instrument and the abstractions used in data interpretation. Here, we introduce a calibration method where interactive live data processing in combination with a digital twin is used to match a set of models and their parameters with the action of a real-world instrument.

physics.ins-det↗

arXiv2023

Effect of intense x-ray free-electron laser transient gratings on the magnetic domain structure of Tm:YIG

Magnetic patterns can be controlled globally using fields or spin polarized currents. In contrast, the local control of the magnetization on the nanometer length scale remains challenging. Here, we demonstrate how magnetic domain patterns in a Tm-doped yttrium iron garnet (Tm:YIG) thin film with perpendicular magnetic anisotropy can be permanently and locally imprinted by high intensity photon pulses of a hard x-ray transient grating (XTG). Micromagnetic simulations provide a qualitative understanding of the observed changes in the orientation of magnetic domains in Tm:YIG and XTG-induced changes. The presented results offer a route for the local manipulation of the magnetic state using hard XTG.

cond-mat.mtrl-sci↗