Composition-structure correlations in strained FexMn1-x/Ir superlattices

The structural and chemical characteristics of FexMn1-x alloys in [FexMn1-x /Ir(001)] superlattices with iron contents of x=0.3, 0.5 and 0.9 are invest igated at the nanometer scale by high resolution transmission electron micr oscopy and electron energy loss spectroscopy techniques. The transmission e lectron microscopy experiments show that pseudomorphic growth of the alloy on Ir is only achieved for x greater than or equal to 0.5. Layers with iron content x=0.5 display, however, structural inhomogeneities and a weak Mn s egregation effect. Layers with a high iron content, Fe0.9Mn0.1 are seen to present a quasiperiodic lattice modulation. We suggest that this modulation is associated with spinodal decomposition. All these structural investigat ions indicate that, in epitaxial strained thin layers, the FexMn1-x alloy r eproduces almost all of the complex FexMn1-x phase diagram with, however, a marked shift towards the low Fe content regions. (C) 2000 American Institu te of Physics. [S0021-8979(00)00121-3].