Combining CXMD and XSW to study magnetic and geometric properties of thin films: Gd/Fe(100)

The magnetic and geometric structure of 1–5 monolayers (ML) of Gd on Fe(100) single crystals has been investigated using synchrotron X-rays between 4 and 8 keV. Choosing a high-flux wiggler beamline made it possible to analyse the magnetic properties by studying the circular X-ray magnetic dichroism (CXMD) and, in addition, to apply the X-ray standing-wave (XSW) technique to elucidate the geometric structure of the overlayers. CXMD reveals that Gd couples antiferromagnetically to the Fe substrate and that 2 ML Gd at 243 K yield a magnetization of ∼22% with respect to the saturation value of a thick Gd foil at 123 K. A magnetic polarization of the Gd pertains even at 308 K. While LEED investigations do not show any long-range lateral order of the Gd film, XSW measurements reveal an ordering of Gd perpendicular to the (100) surface of Fe.