arXiv subjects

F. Kronast

Publications and source records attributed to F. Kronast.

5 recordsLinked to original sources

arXiv2026

Imaging of van der Waals Materials via Standing-Wave Photoemission Microscopy: Depth-Resolved Electronic Structure of WS2

Two-dimensional van der Waals materials promise electronic, optoelectronic, and quantum technologies, yet depth-resolved characterization remains challenging. Here, we demonstrate standing-wave photoemission electron microscopy (SW-PEEM) for Angstrom-scale spectromicroscopy of monolayer WS2 on a W/C multilayer substrate. Tuning the X-ray standing wave through the monolayer yields a chemical depth profile and valence-band modulation with enhanced sensitivity to the top and bottom sulfur layers. X-ray optical modeling determines the structure and field distribution. The measurements reveal an ~0.2 eV shift in sulfur-derived valence-band spectral weight between measurements with enhanced sensitivity to the top and bottom sulfur layers. This shift is unlikely to arise from strong direct substrate hybridization and is instead consistent with sulfur-related surface species, as supported by calculations using a representative elemental-sulfur model. These results establish SW-PEEM as a non-destructive depth-resolved probe, highlighting its potential to probe interfacial coupling, chemical reconstruction, and emergent states in van der Waals and moir\'e systems.

cond-mat.mtrl-sci↗

arXiv2023

Size-dependence and high temperature stability of radial vortex magnetic textures imprinted by superconductor stray fields

Swirling spin textures, including topologically non-trivial states, such as skyrmions, chiral domain walls, and magnetic vortices, have garnered significant attention within the scientific community due to their appeal from both fundamental and applied points of view. However, their creation, controlled manipulation, and stability are typically constrained to certain systems with specific crystallographic symmetries, bulk, or interface interactions, and/or a precise stacking sequence of materials. Here, we make use of the stray field of YBa2Cu3O7-{\delta} superconducting microstructures in ferromagnet/superconductor hybrids to imprint magnetic radial vortices in permalloy at temperatures below the superconducting transition temperature (TC), a method easily extended to other ferromagnets with in-plane magnetic anisotropy. We examine the size dependence and temperature stability of the imprinted magnetic configurations. We show that above TC, magnetic domains retain memory of the imprinted spin texture. Micromagnetic modelling coupled with a SC field model reveals that the stabilization mechanism leading to this memory effect is mediated by microstructural defects. Superconducting control of swirling spin textures below and above the superconducting transition temperature holds promising prospects for shaping spintronics based on magnetic textures.

cond-mat.mtrl-sci↗

arXiv2020

A local view of the laser induced magnetic domain dynamics in CoPd stripe domains at the picosecond time scale

The dynamic of the magnetic structure in a well ordered ferromagnetic CoPd stripe domain pattern has been investigated upon excitation by femtosecond infrared laser pulses. Time-resolved X-ray magnetic circular dichroism in photoemission electron microscopy (TR-XMCD-PEEM) is used to perform real space magnetic imaging with 100 ps time resolution in order to show local transformations of the domains structures. Using the time resolution of the synchrotron radiation facility of the Helmholtz-Zentrum Berlin, we are able to image the transient magnetic domains in a repetitive pump and probe experiment. In this work, we study the reversible and irreversible transformations of the excited magnetic stripe domains as function of the laser fluence. Our results can be explained by thermal contributions, reducing the XMCD amplitude in each stripe domain below a threshold fluence of 12 mJ/cm2. Above this threshold fluence, irreversible transformations of the magnetic domains are observed. Static XMCD-PEEM images reveal the new partially ordered stripe domain structures characterized by a new local magnetic domain distribution showing an organized pattern at the micrometer scale. This new arrangement is attributed to the recovery of the magnetic anisotropy during heat dissipation under an Oersted field.

physics.app-ph↗

arXiv2019

Switching on superferromagnetism

Recent results in electric-field control of magnetism have paved the way for the design of alternative magnetic and spintronic devices with enhanced functionalities and low power consumption. Among the diversity of reported magnetoelectric effects, the possibility of switching on and off long-range ferromagnetic ordering close to room temperature stands out. Its binary character opens up the avenue for its implementation in magnetoelectric data storage devices. Here we show the possibility to locally switch on superferromagnetism in a wedge-shaped polycrystalline Fe thin film deposited on top of a ferroelectric and ferroelastic BaTiO3 substrate. A superparamagnetic to superferromagnetic transition is observed for confined regions for which a voltage applied to the ferroelectric substrate induces a sizable strain. We argue that electric-field-induced changes of magnetic anisotropy lead to an increase of the critical temperature separating the two regimes so that superparamagnetic regions develop collective long-range superferromagnetic behavior.

cond-mat.mtrl-sci↗

arXiv2010

Spin-orbit strength driven crossover between intrinsic and extrinsic mechanisms of the anomalous Hall effect in epitaxial L1o FePd and FePt

We determine the composition of intrinsic as well as extrinsic contributions to the anomalous Hall effect (AHE) in the isoelectronic L1o FePd and FePt alloys. We show that the AHE signal in our 30 nm thick epitaxially deposited films of FePd is mainly due to extrinsic side-jump, while in the epitaxial FePt films of the same thickness and degree of order the intrinsic contribution is dominating over the extrinsic mechanisms of the AHE. We relate this crossover to the difference in spin-orbit strength of Pt and Pd atoms and suggest that this phenomenon can be used for tuning the origins of the AHE in complex alloys.

cond-mat.mes-hall↗