Magnetic force microscopy study of perpendicular magnetization reorientation for Fe grown on Cu/Si(111)

Iron films with thicknesses ranging from 1 ML to 40 ML have been grown on a $\mathrm{Si}\mathrm{}\left(111\right)7\times 7$ reconstructed substrate on which a 15-ML copper layer has been previously deposited. Samples have been analyzed in situ by scanning tunneling microscopy and magnetic force microscopy (MFM) techniques for each step of the iron deposition. Imaging has been performed at room temperature and zero magnetic field. MFM images collected for Fe thickness lower than or equal to 4 ML showed randomly assembled magnetic domains characterized by a perpendicular magnetization. The average magnetic domain size increased with increasing Fe amount up to a thickness of 4 ML. For an Fe film of 6 ML we observed a coexistence of out-of-plane and in-plane magnetic domain structures. The reported magnetic out-of-plane–in-plane transition has been found to occur for iron thicknesses slightly greater than those reported by using electron-diffraction measurements for the structural fcc-bcc transition. For higher iron coverage the presence of domain walls indicated that the thin films are completely magnetized in the plane of the surface. An evaluation of the width of the domains wall is also given.