Irreversibility, reversibility, and thermal equilibrium in domain patterns of Fe films with perpendicular magnetization

We investigate the details of pattern formation and transitions between different modulated phases in ultrathin Fe films on Cu(001). At high temperature, the transitions between the uniform saturated state, the bubble state, and the striped state are completely reversible while at low temperature the bubble phase is avoided. The observed non-equilibrium behavior can be qualitatively explained by considering the intrinsic energy barriers appearing in the system due to the competition between the short-ranged exchange and the long-ranged dipolar interactions. Our experiments suggest that the height of these energy barriers is related to the domain size and is therefore strongly temperature dependent.