Structure and Topology in Nanoscale Magnetic Systems
Understanding the properties and behavior of spin textures in confined nanomagnetic systems is scientifically challenging, but also highly relevant for future technologies. Recently the aspect of topology, in particular the topological protection of novel spin textures, such as magnetic skyrmions, have garnered much interest In this dissertation the relationship of structure and topology to create and control confined magnetic nanostructures through variation of size, composition, and proximity has been investigated experimentally. Requisite nanomagnetic systems were fabricated with state of the art nanofabrication and thin film deposition techniques. They were characterized by a variety of state-of-the-art techniques including various electron and x-ray spectromicroscopies at large scale facilities.
The effect of stray field interactions on the coupling of arrays of nanodisks that exhibit a vortex state spin configuration, as well as so-called XY macrospins revealed the stabilization of collective states with characteristic topologies, that differ from the properties of the individual nanodisks. The insight obtained from that study was used to investigate the transition from paramagnetic magnetic nanoparticle assemblies into a ferromagnetic liquid droplet when jammed through chemical ligands at a liquid-liquid interface.
The vertical coupling in thin film multilayer stacks introduces new ways to control nanoscale spin textures, and led to the stabilization of magnetic skyrmions by varying the thickness and the composition of the multilayers. These studies led to an understanding of the energetic conditions required to stabilize dipolar skyrmion lattices, and subsequenltly, chiral ferrimagnetism .
Interfacing thin film multilayers with strong PMA with confined vortex textures in nanodisks allowed for an imprinting and modification of the spin textures in the combined system. In particular, this study resolved extended topological spin textures, so called nπ target skyrmions, which theoretical predictions identified as precursor for 3D topological spin textures, specifically magnetic Hopfions.
The characteristic spin textures of Hopfions, which are 3D knot-solitons was verified through a combined surface and bulk sensitive x-ray microscopy study.
Investigating the sub-ns dynamics of Hopfions with time-resolved x-ray microscopy studies will open the door to exploit their potential for future application e.g. in spintronic devices.