Atomic-scale visualization and manipulation of topological spin textures in the chiral magnet, MnGe

Topological spin textures in chiral magnets are of fundamental interest and may enable novel magnetic storage and computing technologies. In MnGe, such textures arise from the competition of ferromagnetic exchange, favoring aligned spins, and the Dzyaloshinskii-Moriya interaction (DMI) which favors perpendicular spins. In our spin-polarized STM studies of MnGe thin films, we study spin textures at the surface, where DMI may arise not only from the non-centrosymmetric 'B20' MnGe crystal structure, but also from the surface itself. Furthermore, the thin film structures allow us to study strain effects, and provide a path for integration into heterostructures. Our SP-STM images indicate helical stripe domains with a 6 nm period, which micromagnetic modeling helps us understand as a surface projection of the helical wavevector, which is canted away from the film normal. We can deduce the three-dimensional orientation of the helical wavevectors at domain walls, and we predict that three helical domains can meet in two distinct ways to produce either a 'target-like' or a 'π-like' topological spin texture. Both textures are observed experimentally, and are found in strained regions of the films. Topological defects in the target texture can be created, moved and annihilated with current/voltage pulsing from the STM tip. The core of the target texture itself can be similarly moved, and can also be reversibly switched with applied magnetic field. These studies represent an initial step toward understanding the interplay of bulk and surface magnetism in chiral magnets, and the manipulation of these topological spin textures is a promising step toward future spintronics applications.