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 geom etry, a small uniaxial in plane magnetic anisotropy, whose origin is not to tally understood, is found superimposed to the expected cubic biaxial one. This has a dramatic effect both on the reversal process and the domain stru cture. A combined longitudinal and transversal Kerr study shows the differe nt switching processes (180 degrees walls along the main easy axis versus 9 0 degrees along the secondary easy axis) depending on the relative orientat ion of the magnetic held with respect to the Fe crystallographic axes. Rema rkably, this two- and sometimes three-step switching process appears only w hen the field is applied along certain crystallographic directions. These f indings are corroborated by domain observations. (C) 2000 Elsevier Science B.V. All rights reserved.