GROWTH AND MAGNETIC-PROPERTIES OF COXNI1-X AND FEXNI1-X ULTRATHIN FILMS ON CU(100)

We have grown ultrathin CoxNi1-x and FexNi1-x films on Cu(100) with va rying stochiometry x. We find that these alloy films grow in a fee pha se on Cu(100). With the surface magneto-optic Kerr effect we measured the variation of the Curie temperature T-C as a function of the film t hickness n in monolayers. Fitting an empirical scaling curve to our re sults we are able to extrapolate the value T-C(n=x) for samples with d ifferent stochiometry. We use this framework in order to determine T-C (n=x) for FexNi1-x alloy films, in particular for concentrations close to 65% Fe content. Bulk Fe65Ni35 shows a collapse of magnetic long-ra nge order and a fcc-to-bce structural transition, which is the so-call ed Invar effect. In ultrathin Fe65Ni35 films, we observe a ''quenching '' of the Invar effect, because growth on a Cu(100) substrate forces t he film to adept the Cu lattice spacing thereby suppressing the struct ural relaxation.