Csu Physics Colloquium

The discovery of a new topological form of magnetic order in the family of cubic Dzyaloshinskii-Moriya helimagnets has recently attracted increasing scientific interest. This new magnetic state consists of a lattice of skyrmions, i.e., magnetic vortices characterized by a topological winding number. This implies that skyrmions represent topologicallyprotected magnetic particles with a skyrmion radius  that is a mesoscale length scale and typically of the order of 10200 nm. The mesoscale size together with their topologically protected nature makes them insensitive to atomic-scale defects and impurities and enables them to move independently from the underlying crystal structure. In particular, it has been shown that ultralow current densities of 10 A/m allow moving skyrmions through a material via the spintorque effect. Moving conventional spin-textures such as domain walls requires six orders of magnitude higher currents. Together with the ability to create and delete individual skyrmions via current pulses or polarized spincurrents these novel spin textures have unprecedented potential for low-power/high-density non-volatile racetrack memories and spintronics. Controlling the skyrmion size  is critical for creating future applications based on these spin-textures; for example, for memory devices, small size  (high memory density) is required. However, too small of a size will make skyrmions more susceptible to microscopic defects, and therefore less mobile, requiring larger currents to move them. To first order,  is controlled by two competing magnetic interactions, namely ferromagnetic exchange and the Dzyaloshinskii-Moriya interaction. Here we will report on our extensive neutron scattering studies that reveal the spin dynamics and the underlying magnetic interactions of the prototypical skyrmion compound MnSi.