  Skyrmions are localized, topologically non-trivial spin structures which have
raised high hopes for future spintronic applications. A key issue is skyrmion
stability with respect to annihilation into the ferromagnetic state. Energy
barriers for this collapse have been calculated taking only nearest neighbor
exchange interactions into account. Here, we demonstrate that exchange
interactions beyond nearest neighbors can be essential to describe stability of
skyrmionic spin structures. We focus on the prototypical film system
Pd/Fe/Ir(111) and demonstrate that an effective nearest-neighbor exchange or
micromagnetic model can only account for equilibrium properties such as the
skyrmion profile or the zero temperature phase diagram. However, energy
barriers and critical fields of skyrmion collapse as well as skyrmion lifetimes
are drastically underestimated since the energy of the transition state cannot
be accurately described. Antiskyrmions are not even metastable. Our work shows
that frustration of exchange interactions is a route towards enhanced skyrmion
stability even in systems with a ferromagnetic ground state.
