  Spin polarized scanning tunneling microscopy is used to directly image
topological magnetic textures in thin films of MnGe, and to correlate the
magnetism with structure probed at the atomic-scale. Our images indicate
helical stripe domains, each characterized by a single wavevector Q, and their
associated helimagnetic domain walls, in contrast to the 3Q magnetic state seen
in the bulk. Combining our surface measurements with micromagnetic modeling, we
deduce the three-dimensional orientation of the helical wavevectors and gain
detailed understanding of the structure of individual domain walls and their
intersections. We find that three helical domains meet in two distinct ways to
produce either a "target-like" or a "pi-like" topological spin texture, and
correlate these with local strain on the surface. We further show that the
target-like texture can be reversibly manipulated through either
current/voltage pulsing or applied magnetic field, a promising step toward
future applications.
