Controlling the formation and properties of topological magnetic phenomena

Throwing a stone into water excites a wave that decays in distance and time. However, some wave-like phenomena, known as topological objects (TOs), don't behave like this. They are localised in space and trapped in existence for long periods of time. Many such TOs are found in magnetic materials (e.g. domain walls and, latterly, the more exotic skyrmions), but significantly more have been stabilised recently, including hopfions, blochions and merons. Topology provides the organising principle to understand the extraordinary properties of TOs, but also the classification of topological states (TS) of matter, including topological electronic structure and topological order. Magnetic phenomena in materials are some of the oldest discoveries of science and continue to be some of the technologically most useful. Despite this, an understanding of topological magnetism (TM) is relatively recent and is undergoing a rapid change, with key discoveries of new physics, materials and applications. TM systems have a wealth of potentially useful properties and excitations. However, the exploitation of topological magnetic effects in technology is in its infancy and is the long-term motivation of our project, with its combination of materials development and fundamental scientific investigation. The discovery of exotic TOs in magnetic materials and their potential for use as high-density, low-energy components in magnetic storage and in computation applications has made topological magnetism one of the hottest topics in worldwide physics research. The related investigation of TSs has also undergone rapid expansion, and the exploitation of topological states and excitations now holds promise for applications. What the field of TM lacks is the ability to control the topological properties of well-characterized magnetic materials. We will address this fundamental problem to achieve a step-change in the exploitation of topological magnetic states and excitations through the manipulation and elucidation of novel material systems. Our project is organised around two Work Package Clusters, whose key aims are: -Cluster 1 (C1): synthesise/characterize bulk topological-magnetic systems; -Cluster 2 (C2): using a host of techniques including x-ray, neutron and muon spectroscopy, determine the topological properties of novel magnetic TSs and TOs, especially where TOs and TSs coincide/interact, and develop methods to control them. The specific objectives are: C1: -Identify candidate materials exhibiting unconventional spin textures and topological and magnetic states; produce high-quality single crystals. -Optimise their structural, magnetic and electrical properties through chemical and physical manipulation, to promote contol over the topological elements. -This cluster will initially target a number of materials classes for investigation, before concentrating on the most promising. Our target materials classes include: -Frustrated kagome systems hosting magnetic topological phases such as Fe3Sn2 and RMn6Sn6. -Weyl semimetals/Dirac materials of the type RAlX (R=Ce, Pr; X=Si, Ge) -Intermetallics with the ThCr2Si2 structure proposed as hosts of topological structures, such as GdRu2Si2, REMn2Ge2 (RE=rare earth). -Spin liquid candidate materials Na3Co2SbO6 and Na2Co3TeO6. C2: -Determine which novel TOs, previously only stabilized in artificial structures, can be found intrinsically in bulk single-crystal systems; -Elucidate the role of three-dimensional magnetic structure in the stability and properties of those TOs usually treated as purely two-dimensional; -Characterize and control the dynamic processes that dominate the responses of TOs and TS; -Determine and control the ground states, TOs, and TSs occurring in exotic TM systems.