Research Examples

Direct imaging of spin waves

The use of spin-wave signals in future information processing devices can substantially reduce power consumption over present charge current based technologies. In this spirit, we are investigating the underlying fundamental physics of spin-wave dynamics by means of time-resolved direct magnetic imaging.

Time-resolved imaging of topological magnetic structures

In this project, we are investigating the dynamical properties of topological magnetic structures. A substantial attention is dedicated to the investigation of the static and dynamic behavior of magnetic skyrmions. Magnetic skyrmions, thanks to their physical and topological stability, of extreme interest in spintronics, as their properties can allow, if the skyrmions are used as magnetic data bits, to overcome many of the current limitations of conventional magnetic hard drives. However, before magnetic skyrmion devices can be devised, it is necessary to characterize both the static and dynamical properties of the magnetic skyrmions in different materials and conditions. Here, thanks to the high temporal and spatial resolution of scanning transmission x-ray microscopy, we are investigating the nucleation, propagation, and annihilation of magnetic skyrmions in device-relevant geometries.

This project is being carried out in the framework of the EU Horizon 2020 "MAGicSky" project.

Magneto-elastic coupling

The magnetic configuration of magnetostrictive materials (such as e.g. Ni, Galfenol, Terfenol-D) can be influenced, through the inverse magnetostrictive (or magneto-elastic) coupling, by the application of a suitable mechanical strain. The magneto-elastic coupling can be employed for the fabrication of artificial multiferroic materials (e.g. by combining a magnetostrictive and a piezoelectric material). However, if such material is to be employed, the properties of the magneto-elastic coupling need to be investigated in detail. While the quasi-static properties of the magneto-elastic coupling have been well characterized in the past, its influence on the dynamical processes of the magnetization is still obscure. Our research in this project is therefore aimed at the analysis of the effect of static and dynamic mechanical strain on the dynamical processes of the magnetic configuration of magnetostrictive materials. One of such projects involves the analysis of the motion (resolved to sub-nanosecond timescales) of magnetic vortex cores in different magnetostrictive materials as a function of an applied static mechanical strain.

Quantitative imaging of polymer blend nanostructures

Conjugated polymers have electrically conducting or semi-conductor properties and can be used to make optoelectronic devices such as solar cells and light emitting diodes (LEDs) where the active material is a polymer, rather than silicon. Since polymers have much lower charge screening than silicon, a polymer-based solar cell needs some help to split the charges generated by absorbing light, by providing an interfaces between two organic semiconductors with different electron affinities. A "bulk heterojunction" device uses a blend of conjugated polymers (or a polymer and a buckminster-fullerene derivative) to create lots of interfaces for efficient charge splitting, however this may come at the cost of efficient charge transport if the material domains don't always connect to the electrodes at either side of the device. Spectro-microscopy with STXM provides high resolution imaging with strong, natural contrast based on the molecular structure of the components (not just elements!) that can be used to calculate quantitative composition maps of blend films. Quantitative studies of changes in blend films with changes in fabrication or annealing parameters provide insights into the underlying physics of material diffusion and segregation and allow researchers to optimise device nanostructure in order to produce more efficient devices and also more accurately assess new conjugated polymer materials.

Molecular orientation mapping and control

Many properties of conjugated polymers depend strongly on the alignment and orientation of the polymer chains. Linear dichroism effects allow STXM measurements to quantitatively map the degree of alignment and preferred direction of the polymer chains, which aids researchers in understanding the operation of polymer-based devices such as field-effect transistors (FETs), light emitting diodes (LEDs) and lasers. Better control over the molecular orientation of conjugated polymer films would significantly improve the efficiency of such polymer-based devices.

We are also involved in the development and improvement of the instrumentation available at the PolLux and NanoXAS beamlines at the Swiss Light Source. Some examples of developed instrumentation include:

• Pixelator STXM control software
• Setup for the acquisition of time-resolved STXM images with sub-nanosecond temporal resolution
• Sample holders designed for high frequency experiments
• Setup for the in-situ generation of magnetic fields up to ca. 200 mT at 0, 30, and 90 degrees orientations
• Setup for the in-situ mechanical straining of membranes
• Gas-flow environmental cell (together with the Surface Chemistry group