The magnetic coupling between epitaxial single-crystalline Co and FeMn layers on Cu(001) was investi-gated by element-resolved magnetic circular dichroism domain imaging using a photoelectron emission mi-croscope. As-grown Co domain patterns reveal the presence of many small domains in the antiferromagnet. The coupling of the Co layer is found to be along (100) crystallographic directions. This is discussed in terms of a 45° coupling due to frustrations at topological 90° domains in the FeMn layer. Coercivity oscillations as a function of FeMn thickness with atomic monolayer period support the importance of such step-induced domains in the coupling.