Structure of Mn films grown on (111) and (001)fcc Ir determined by EXAFS and the multiple-scattering approach

Mn films were grown on (001) and (111) fcc Ir lattices by molecular beam epitaxy, extended x-ray absorption fine structure (EXAFS) experiments were performed on these films in order to determine the Mn structures. As Mn can adopt different crystalline structures, it is first shown that the usual Fourier treatment of EXAFS oscillations is not an appropriate technique for this purpose. On the contrary, the application of multiple scattering theory of x-ray-absorption fine structure allows us to identify the structures. For relaxed (polycrystalline) thick Mn deposits, Mn crystallizes in the Mn alpha structure. For unrelaxed (single-crystalline) thick Mn films, the Mn EXAFS oscillations are well simulated assuming a mixing of fee and Mn alpha structure. For thin Mn films in Mn/Lr (111) and (001) superlattices, this multiple scattering approach allows us to show that Mn is in a trigonal structure when it is grown on Ir(111) and a tetragonal structure when it is grown on Ir(001). Finally, the (root 3 x root 3)R30 degrees superstructure of Mn films grown on (111) Ir is shown to come from the epitaxy of a mixed fee and Mn alpha structures and not from the occurence of Mn Laves phases like Cu2Mg or Zn2Mg as assumed by several workers.