Variable magnetic field magnetic force microscopy of the magnetization reversal in epitaxial iron (1 1 1) thin films

The magnetization reversal in epitaxial iron 〈1 1 1〉 films has been studied using MFM with in situ magnetic fields and, in addition, correlated with macroscopic data obtained by conventional magnetometry. Due to the crystallographic orientation and growth-related strain of the films, they do not have an in-plane magnetic easy axis which results in a fine stripe domain pattern in zero magnetic field. The observed zero field stripe period and the critical thickness for stripe formation in the films are in approximate agreement with theory. The magnetization reversal in these films can be described in terms of two distinct regimes: the 'fast' regime in which the in-plane magnetization of magnitude approximately half the saturation magnetization reverses in a narrow field range around the coercive field (of approximately 100 Oe), and the 'slow' regime at higher fields where the in-plane magnetization gradually increases toward saturation along the applied field. The salient features in the 'fast' regime shown by the MFM data are subtle: the positions of the stripes do not change indicating that the out of plane magnetization components are not altered; and the only clearly observable change is a reduction in the number of forks or defects in the stripe pattern. As the field is further increased through the 'slow' regime, the stripe domain period decreases. In addition, in the high field region where the bulk hysteresis loop data indicate the magnetization to be reversible, the MFM data clearly indicate that the magnetization process is irreversible with the average stripe width observed to be smaller in decreasing the field after saturation.