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 anomalou s magnetic in-plane anisotropy even in the monolayer limit whereas perpendi cular anisotropy can be achieved only by depositing iron layers at lower te mperature. The structure of the RT grown films and its influence on the mag netic properties are examined. In order to clarify the growth at RT, we hav e performed core level photoemission, LEED and SEXAFS on ultrathin Fe/Pd(10 0) layers. By photoemission, we observe a core level shift which is attribu ted to the interdiffusion of the first iron layers into the Pd(100) substra te. SEXAFS measurements confirm a surface alloying up to four equivalent mo nolayers Fe/Pd(100). At this coverage, polarization dependent SEXAFS result s are compatible with a face-centered-tetragonal Fe-55/Pd-45 disordered all ey structure showing an expansion of 4% of the lattice parameter in the gro wth direction. The magnetic in plane anisotropy observed by Kerr on ultrath in Fe films and the large orbital moment measured on the Fe L-2,L-3 edges a re understood in the light of the microscopic description of the Fe/Pd(100) interface. [S0163-1829(99)01830-5].