Influence of structural characteristics on magnetic properties in face-centered-tetragonal surface alloy of Fe/Pd(100) ultrathin films

Ultrathin Fe layers grown at room temperature (RT) on Pd(100) show anomalous magnetic in-plane anisotropy even in the monolayer limit whereas perpendicular anisotropy can be achieved only by depositing iron layers at lower temperature. The structure of the RT grown films and its influence on the magnetic properties are examined. In order to clarify the growth at RT, we have performed core level photoemission, LEED and SEXAFS on ultrathin Fe/Pd(100) layers. By photoemission, we observe a core level shift which is attributed to the interdiffusion of the first iron layers into the Pd(100) substrate. SEXAFS measurements confirm a surface alloying up to four equivalent monolayers Fe/Pd(100). At this coverage, polarization dependent SEXAFS results are compatible with a face-centered-tetragonal ${\mathrm{Fe}}_{55}{/\mathrm{P}\mathrm{d}}_{45}$ disordered alloy structure showing an expansion of 4% of the lattice parameter in the growth direction. The magnetic in plane anisotropy observed by Kerr on ultrathin Fe films and the large orbital moment measured on the Fe $L_{2,3}$ edges are understood in the light of the microscopic description of the Fe/Pd(100) interface.