Imaging of magnetic domain walls in iron with a magnetic force microscope: A numerical study

A two-dimensional, numerical, micromagnetic model was applied to understand the images of 180^∘{} walls in iron thin films obtained with a magnetic force microscope (MFM). Assuming the tip stray field would not affect the wall magnetization, the model predicts a contrast well below the sensitivity of the MFM. However, this assumption is unrealistic. The inclusion of the tip stray field in the simulation shows that the domain wall is polarized by the tip stray field. The resulting contrasts from the polarized walls differ drastically from the contrasts expected from undisturbed walls but agree well with experimental observations. Such polarization effects make the authors doubtful about the applicability of the MFM to studies of other micromagnetic phenomena in soft magnetic materials.