Direct observation of magnetic instabilities in NiO thin films epitaxially grown on Fe(0 0 1)

We study, by means of X-ray magnetic linear dichroism (XMLD) and photoemission electron microscopy (PEEM), the magnetic instabilities in the NiO/Fe(0 0 1) system, as a function of the NiO film thickness. For NiO films thinner than a critical thickness of about 10 ML the NiO AFM moments align in-plane perpendicular to the Fe substrate magnetization. Just above the critical thickness the coupling turns out to be collinear. The behavior for very large NiO thicknesses (up to about 80 ML), studied by applying an external magnetic field, shows a complete reversal of the NiO domains, for a 90° rotation of the substrate magnetization. Furthermore, a decreasing trend of the NiO XMLD signal as a function of the AFM film thickness is shown. These findings are discussed and tentatively explained in terms of defects occurring at the interface and/or in the NiO volume.