Structure and magnetism of ultrathin epitaxial Fe on Ag(100)

Abstract

We have made in-situ investigations of ultrathin films of Fe grown on a Ag(100) single crystal. This system is known to exhibit a reorientation of the magnetization, dependent on both Fe thickness and temperature. X-ray absorption fine structure has been recorded for samples prepared in-situ, both in the near edge and in the extended x-ray absorption fine structure (EXAFS) region. Using x-ray magnetic circular dichroism we found that Fe films between 2--5 monolayers show an out-of-plane remanent magnetization. For thicker films the magnetization lies in-plane. By applying the magneto-optical sum rules we found an enhancement of the orbital moment $({m}_{l})$ for the out-of-plane phase, whereas the spin moment $({m}_{s})$ is unchanged. From the Fe $L$-edge EXAFS, we obtain information on the local crystallographic structure. A strong correlation between the local crystallographic structure and the magnetic properties is found for the $\mathrm{Fe}∕\mathrm{Ag}(100)$ system. Variations in the nearest neighbor distance of $\ensuremath{\sim}0.15\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ are observed when comparing 3 ML and 25 ML films. By comparison to simulations performed with the FEFF 8.10 code, we can identify a bcc structure for 6--25 ML Fe on Ag(100). For the 3 ML Fe film our simulations indicate strong deviations from any structure derived along the Bain path. We conclude that intermixing and distortion are important to describe the structure in this thickness range.