Magnetic Structures and Dynamics in Skyrmion Hosting Materials

Abstract

Magnetic skyrmions are topologically non-trivial, vortex-like self-assemblies of magnetic moments which have been heralded for the advantages they bring to next-generation computing elements. Their robustness against perturbation, countable nature, and emergent dynamical phenomena offer significant potential in a range of applications from data storage, through to novel neuromorphic computing schemes. In designing such skyrmionic devices, it is pertinent to completely understand their microscopic structure and dynamical properties. In this thesis, we use a combination of x-ray and neutron scattering techniques, and electrical transport measurements to investigate the magnetic structures and their emergent dynamics in a range of skyrmion materials and candidates.

Resonant soft x-ray diffraction with polarisation analysis is used to refine the magnetic structures in Cu2OSeO3, which until now have remained elusive. The contribution from anisotropic tensor scattering is addressed, and the magnetic structures are found to be elliptically modulated. We discuss surface effects, and complexities in refining the structure of the skyrmion lattice.

Next we investigate the emergent electromagnetic properties of the skyrmion lattice and their dynamics in the prototypical skyrmion host, MnSi. We find that inertial and deformative dynamics induce an out-of-phase emergent electric field. We term this effect emergent reactance and describe its origin phenomenologically. We then continue the studies of dynamics by demonstrating a novel device concept in a three-dimensional structure of FeGe. in which the skyrmion lattice can be isothermally injected in a metastable regime. We then discuss the applicability of such a mechanism within current device regimes.

Finally, using x-ray and neutron scattering techniques we search for new skyrmion materials and investigate the candidate host EuGa2.4Al1.6. We find a complex interplay between charge and magnetic order, including a potential mixed multi-Q phase. However, we find no signatures of a skyrmion phase.