Simple structure and soft elastic behavior of Mn on Fe{001}

Ultrathin films of Mn grow epitaxially and pseudomorphically on Fe{001}. Low-energy electron diffraction (LEED) experiments show that with increasing thickness the films contain defects and disorder, but a substantial portion remains well crystallized. A quantitative LEED analysis of a 23-Å-thick film finds that the film has a body-centered-tetragonal structure with lattice parameters: a=2.866 Å and c=3.228 Å, hence with an axial ratio c/a=1.13 and atomic volume 13.3 A${\mathrm{̊}}^3$/atom. Strain analysis using both the LEED results and the tetragonal structure from dilute Mn alloys determines the Poisson ratio of the film to be near 0.5, hence the film is elastically soft. Both the face-centered- and the body-centered-cubic structures are consistent with the data as underlying phases of the grown film. LEED intensity data show that the distance between Mn layers is small (about 1.3 Å) when the epitaxial film is only two- or three-layers thick, and then increases to become 1.614 Å in the bulk of 14-layer thick films. © 1996 The American Physical Society.