Stripe width and nonlocal domain walls in the two-dimensional dipolar frustrated Ising ferromagnet

We describe a type of magnetic domain wall that, in contrast to Bloch or Néel walls, is nonlocalized and, in a certain temperature range, nonmonotonic. The wall appears as a mean-field solution of the two-dimensional ferromagnetic Ising model frustrated by a long-ranged dipolar interaction. We provide experimental evidence of this wall delocalization in the stripe-domain phase of perpendicularly magnetized ultrathin magnetic films. In agreement with experimental results, we find that the stripe width decreases with increasing temperature and approaches a finite value at the Curie temperature following a power law. The same kind of wall and a similar temperature dependence of the stripe width are expected in the mean-field approximation of the two-dimensional Coulomb frustrated Ising ferromagnet.