Speaker
Description
The interplay between spin-orbit interaction (SOI) and magnetic order is currently one of the most active research fields in condensed matter physics. Famous examples of this interplay are skyrmions and spin waves, but also the unique properties of altermagnets, the search for Majorana zero modes, and magnetic topological insulators fit directly in this field and have gained much attention in recent years. The full spectrum of possibilities is unleashed in combination with breaking the symmetry of the system, either at interfaces or in the crystal structure itself. This makes multiferroic materials, where symmetry breaking in the form of ferroelectric order and magnetic order coexist, a promising playground to look for functional properties combining SOI and magnetism. Here we will show that starting from a ferroelectric system with strong spin orbit interaction and doping this with magnetic impurities is ndeed a promising pathway to achieve magnetic order with tuneable dynamics. The switching mechanism in this correlated spin glass system will be explained based on stochastic resonance. Furthermore, it will be shown how photocurrents can be used to control the topological spin textures.
In $\alpha$-GeTe the combination of the ferroelectric order and large SOI yields a switchable Rashba-type spin structure of the bulk states. When doped with up to 20$\%$ Mn a magnetic order is induced while the ferroelectric order remains present, rendering it a multiferroic material. Moreover, the strong magnetoelectric coupling in the system ensures a coupling of the magnetisation and polarisation axes, resulting in the opening of a Zeeman gap in the Rashba split bands around the Brillouin zone centre. This unique combination of properties creates a large bulk Rashba-Edelstein effect and allows for current driven magnetisation switching. Here we will present X-ray magnetic circular dichroism (XMCD) and muon spin resonance (muSR) results supported by theory showing that the system orders in a correlated spin glass state with topological spin textures and spontaneously switches its magnetisation direction without changing any of the typical external parameters.
