  We have employed spin-polarized scanning tunneling microscopy and Monte-Carlo
simulations to investigate the effect of lateral confinement onto the
nanoskyrmion lattice in Fe/Ir(111). We find a strong coupling of one diagonal
of the square magnetic unit cell to the close-packed edges of Fe
nanostructures. In triangular islands this coupling in combination with the
mismatching symmetries of the islands and of the square nanoskyrmion lattice
leads to frustration and triple-domain states. In direct vicinity to
ferromagnetic NiFe islands, the surrounding skyrmion lattice forms additional
domains. In this case a side of the square magnetic unit cell prefers a
parallel orientation to the ferromagnetic edge. These experimental findings can
be reproduced and explained by Monte-Carlo simulations. Here, the single-domain
state of a triangular island is lower in energy, but nevertheless multi-domain
states occur due to the combined effect of entropy and an intrinsic domain wall
pinning arising from the skyrmionic character of the spin texture.
