  The large epitaxial stress induced by the misfit between a triple atomic
layer Fe film and an Ir(111) substrate is relieved by the formation of a dense
dislocation line network. Spin-polarized scanning tunneling microscopy (SP-STM)
investigations show that the strain is locally varying within the Fe film and
that this variation affects the magnetic state of the system. Two types of
dislocation line regions can be distinguished and both exhibit spin spirals
with strain-dependent periods (ranging from 3 nm to 10 nm). Using a simple
micromagnetic model, we attribute the changes of the period of the spin spirals
to variations of the effective exchange coupling in the magnetic film. This
assumption is supported by the observed dependence of the saturation magnetic
field on the spin spiral period. Moreover, magnetic skyrmions appear in an
external magnetic field only in one type of dislocation line area, which we
impute to the different pinning properties of the dislocation lines.
