# Transient magnetic domain wall AC dynamics by means of MOKE microscopy

## TL;DR

This study investigates the complex transient behavior of magnetic domain walls in ferromagnetic films under alternating magnetic fields using MOKE microscopy, revealing unexpected phenomena beyond traditional models.

## Contribution

It uncovers novel transient dynamics of domain walls under AC fields in the creep regime, extending understanding beyond constant field predictions and small fluctuation limits.

## Key findings

- Domain walls evolve toward distorted shapes after multiple AC cycles.
- Transient evolution can be characterized by alternative observables beyond roughness exponent.
- Final stationary states and underlying physics are discussed.

## Abstract

The domain wall response under constant external magnetic fields reveals a complex behavior where sample disorder plays a key role. Furthermore, the response to alternating magnetic fields has only been explored in limited cases and analyzed in terms of the constant field solution. Here we unveil phenomena in the evolution of magnetic domain walls under the application of alternating magnetic fields within the creep regime, well beyond a small fuctuation limit of the domain wall position. Magnetic field pulses were applied in ultra-thin ferromagnetic films with perpendicular anisotropy, and the resulting domain wall evolution was characterized by polar magneto-optical Kerr effect microscopy. Whereas the DC characterization is well predicted by the elastic interface model, striking unexpected features are observed under the application of alternating square pulses: magneto-optical images show that after a transient number of cycles, domain walls evolve toward strongly distorted shapes concomitantly with a modification of domain area. The morphology of domain walls is characterized with a roughness exponent when possible and contrasted with alternative observables which result to be more suitable for the characterization of this transient evolution. The final stationary convergence as well as the underlying physics is discussed.