We image the domain patterns in perpendicularly magnetized ultrathin Fe films on Cu(100) as a function of the temperature T and the applied magnetic field H. Between the low-field stripe phase and the high-field uniform phase we find a bubble phase, consisting of reversed circular domains in a homogeneous background. The curvature of the transition lines in the H-T parameter space is in contrast to the general expectations. The pattern transformations show yet undetected scaling properties.

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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 twodimensional Coulomb frustrated Ising ferromagnet.

We propose a scaling hypothesis for pattern-forming systems in which modulation of the order parameter results from the competition between a short-ranged interaction and a long-ranged interaction decaying with some power α of the inverse distance. With L being a spatial length characterizing the modulated phase, all thermodynamic quantities are predicted to scale like some power of L, L △(α,d) . The scaling dimensions △(α, d) only depend on the dimensionality of the system d and the exponent α. Scaling predictions are in agreement with experiments on ultra-thin ferromagnetic films and computational results. Finally, our scaling hypothesis implies that, for some range of values α > d, Inverse-Symmetry-Breaking transitions may appear systematically in the considered class of frustrated systems.

Ultrathin Fe films on Cu(1 0 0) are self-organized into stripes of opposite perpendicular magnetization. The process of self-organization involves stripe-nucleation and stripe-creep. We present images of nucleation and creep at the micrometre scale. These observations provide evidence of both quenched and self-induced disorder in a system with competing interactions.