Magnetic Skyrmions on the Move
Abstract: Magnetic skyrmions are topologically stable magnetic spin textures that have been discovered in materials with Dzyaloshinskii-Moriya interactions. On one hand, the controlled manipulation of magnetic skyrmions in thin films at room temperature are envisioned to enable skyrmion-based spintronics, which would lead to energy-efficient device applications, such as memory for computers. On the other hand, there is the fundamental question as to whether for quasi-particles with a topological charge, like skyrmions, there is a Hall effect, analogous to the ordinary Hall effect of electrically charged particles.
In this presentation, I will discuss our work demonstrating how in thin film heterostructures, inhomogeneous electric charge currents combined with the spin Hall effect in a heavy metal layer can be used to generate and manipulate magnetic skyrmions in an adjacent ferromagnetic layer. Skyrmions, visualized using magneto-optical Kerr effect microscopy, are generated via diverging electric charge currents from stripe domains in a process that appears stunningly similar to droplet formation in surface-tension driven fluid flow. These experiments importantly demonstrate the stabilization of magnetic skyrmions at room temperature, a necessary requirement for any future application. Furthermore, we find that under application of sufficiently large homogeneous currents, the motion of magnetic skyrmions contains both longitudinal and transverse components, evidencing the skyrmion Hall effect. Interestingly, the derived skyrmion Hall angle is shown to first increase with increasing current density, after which it saturates. The behavior indicates pinning due to defects plays a role in determining the dynamics of the skyrmions. The dependence of the sign of the skyrmion Hall angle on the topological charge (+/-1) is demonstrated, illustrating the potential for topological sorting.