Morphology of Fe/Pd(100) films studied using photoemission from physisorbed Xe

The system Fe/Pd(100) exhibits a strong thickness dependence of the Curie temperature TC, especially in the submonolayer range. Also, the magnetic properties of ultrathin Fe/Pd(100) films depend on the growth temperature. Films grown at 100 K possess easy axes of magnetization that are perpendicular to the film plane for monolayer-range Fe thicknesses, while films grown at 300 K have in-plane easy axes for all thicknesses. In the present study, photoemission (using He i radiation, 21.2 eV) of physisorbed Xe monolayers on Pd(100) and Fe/Pd(100) at 50 K has been used to study the morphology that underlies the magnetic properties. Xe adsorbed on clean Pd(100) shows narrow Xe 5p3/2 and 5p1/2 emission peaks. The peaks broaden and shift toward higher binding energies for adsorption on the Fe/Pd(100) films. In the case of 100-K growth, the peak shift reaches maximum upon the completion of one monolayer of Fe, while for 300-K growth the shifting occurs gradually over several Fe monolayers. No splittings are observed for either the 5p3/2 or 5p1/2 emission peak, suggesting the absence of Fe islands on the Pd(100) substrate even in the submonolayer Fe regime, which is consistent with a random-site-occupancy model that has been proposed recently in a theoretical study of the TC variation.