Degradation of domains with sequential field application

Recent experiments show striking unexpected features when sequences of alternating magnetic field pulses are applied to ferromagnetic samples: domains show area reduction and domain walls change their geometrical properties. In this work, we use a simple scalar-field model which only considers two preferential values for an order parameter, short-range exchange, disorder, and temperature. By proposing a numerical protocol that mimics the experimental one, we show that domains described by the model are also subject to area reduction under sequential field application. We study two domain geometries common in ferromagnetic films: a bubble and a stripe domain. In both cases, the area reduction as a function of the number of alternating field cycles follows a linear combination of an exponentially and a linearly decreasing functions, as reported for the experiments. We characterize the domain walls geometry by computing its roughness exponents. The obtained roughness exponents are indistinguishable from the ones observed experimentally under alternating fields and also when the standard protocol to measure velocities is numerically emulated.