Magnetization reversal asymmetry in Fe/MgO(001) thin films

We study the in-plane magnetization process in 200 Angstrom Fe(0 0 1) thin films grown by sputtering at normal incidence. In spite of this growth geometry, a small uniaxial in plane magnetic anisotropy, whose origin is not totally understood, is found superimposed to the expected cubic biaxial one. This has a dramatic effect both on the reversal process and the domain structure. A combined longitudinal and transversal Kerr study shows the different switching processes (180 degrees walls along the main easy axis versus 90 degrees along the secondary easy axis) depending on the relative orientation of the magnetic field with respect to the Fe crystallographic axes. Remarkably, this two- and sometimes three-step switching process appears only when the field is applied along certain crystallographic directions. These findings are corroborated by domain observations. (C) 2000 Elsevier Science B.V. All rights reserved.