Speaker
Description
Low-dimensional magnetism continues to be of great theoretical and experimental interest, as reduced dimensionality supports strong fluctuations that can result in novel states and excitations. One theme in this field is the understanding of magnetism in reduced dimensions using notions from topology. Examples include topological objects such as walls, vortices and skyrmions, which can potentially exist in the spin textures of a range of systems. In recent years, the experimental discovery of skyrmions in magnetic materials and of their self-organization into a skyrmion lattice, together with their potential for use as high density, low-energy sensors and magnetic storage, has made the investigation of such magnetic topological objects particularly important$^{1}$.
Here we report insights gained from our muon-spin spectroscopy ($\mu^{+}$SR) investigations of materials with topological excitations, including: (i) order and dynamics in GaV$_{4}$S$_{8-y}$Se$_{y}$, a system hosting Néel skyrmions in which $\mu^{+}$SR shows how their stability is enhanced through chemical substitution and the application of pressure$^{2}$; (ii) the skyrmion-hosting multilayer system Ta/[CoFeB/MgO/Ta]$_{16}$, where low-energy $\mu^{+}$SR uniquely reveals changes in the magnetic structure with depth into the multilayer stack; (iii) Cr$_{1/3}$NbS$_{2}$, which hosts topological soliton excitations, and where we show that the magnetism is determined directly by features in the electronic bandstructure$^{3}$. These investigations demonstrate how the combination of $\mu^{+}$SR, magnetometry and electronic structure calculations, both to determine muon sites and more generally, can be used to achieve additional insights into the underlying magnetic behaviour.
$^{1}$T. Lancaster, Contemp. Phys. 60, 246 (2019). $^{2}$T.J. Hicken et al., Phys. Rev. Research 2, 032001(R) (2020); Phys. Rev B 105, 134414 (2022). $^{3}$T.J. Hicken et al. Phys. Rev. B 105, L060407 (2022).
