“Skyrmions in confined spaces: A local-scale SPM analysis”

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In this project, we apply our dedicated scanning-probe (SPM) methods (i.e. Magnetic Force Microscopy (MFM), Piezoelectric Force Microscopy (PFM), and Kelvin Probe Force Microscopy (KPFM), etc.) to the fundamental analysis of skyrmion (SKY)-hosting thin-films and nanostructures. Additionally, these SPM methods will also be used to either locally or globally induce SKY manipulation in these thin films, both by electrical, magnetic, and mechanical means. We hence profit here from our vast SPM experience having investigated SKYs and skyrmion lattices (SkLs) at the surface of the B20, the Cu2OSeO3, and GaV4S8-(GVS)-family-type bulk materials. The GVS systems are very favorable, since being multiferroic semiconductors, which is in favor for both, exploring the mutual interplay of ferroelectric and magnetic textures (SkLs) in thin-films including the contribution of bulk and interfacial Dzyaloshinskii-Moriya-interaction (DMI), as well as inducing changes in the magnetic SKY texture solely by electrical means. A third way of field stimuli (beyond electrical and magnetic) that is explored here is mechanical stress, as exerted onto the thin film either through epitaxial misfit, or when being mounted onto a piezoelectric substrate carrier for linear contraction / expansion. These manipulations will all be performed in-situ, hence providing additional degrees of freedom when recording the extended phase diagrams of such films. The central focus in this project lies on thin-film samples of the GVS-family that will be prepared with reduced dimensions, i.e. samples confined to 2-dimensional (2D), 1D, and 0D nanostructures. This is realized by applying 4 different preparation routes, i.e. two top-down and two bottom-up strategies: thinned-down bulk thin films will be realized either through Focused-Ion-Beam -Milling or Chemical-Mechanical-Polishing with the goal to reach ~50-nm-thick, free-standing thin films. The bottom-up approaches include the GVS-sample-growth by Pulsed Laser Deposition and using single grains of polycrystalline GVS as 0D nanostructures. A specialty introduced here are wedge-like sample-cuts, that allow to in-situ investigate the different competing interactions by SPM at buried interfaces. In addition, we focus our SPM research also on a second class of thin-film SKY materials, i.e. SrIrO3 / SrRuO3 multilayers. In contrast to the GVS-type samples, interfacial DMI between individual (mono)layers stands in our focus here. Again, the full analysis by the SPM methods as well as the local manipulation of SKYs will be realized. -- Note that investigating these two prominent and novel sample systems, i.e. the GVS-type and oxide thin-films, will uniquely be possible through applying our elaborated SPM methods; no other (real or reciprocal-space) technique is known to date that might deliver as much insight into these nanoscale systems. Hence, our methodologies might equally be applied to other prospective materials within this SPP.