GROWTH OF FEXNI1-X ULTRATHIN FILMS ON CU(100) NEAR THE INVAR CONCENTRATION

We have grown ultrathin FexNi1-x films epitaxially on Cu(100) with dif ferent stoichiometry. Previous measurements showed a deviation of the thickness dependence of T-c for a Fe75Ni25 alloy, which was not observ ed for smaller Fe concentrations. Therefore, we investigated the growt h near this invar concentration more closely. With a charge coupled de vice camera based acquisition system, we observed the evolution of the reflection high-energy electron diffraction pattern during growth nea r the invar concentration. This allows us to determine the in-plane la ttice constant of the top layer. Up to 66% Fe content, we see in-plane lattice constant oscillations similar to the Co/Cu(100) system [Fassb ender et al., Phys. Rev. Lett. 75, 4476 (1995)]. At 80% Fe content, th ese oscillations are suppressed and we observe also a lattice contract ion as expected from recent calculations. We discuss these results in connection with our previous results on the magnetic properties of Fex Ni1-x ultrathin films. (C) 1997 American Institute of Physics.