We set out to compare the ferromagnetic behavior of FexNi(1−x)and CoxNi(1−x)films of varying stoichiometry epitaxially grown on Cu(100). The thickness chosen was 5 ML over a wide alloy composition range. Using a scaling law for the thickness vs Curie temperature, we extrapolate the bulk fcc film thickness and plot the bulk fcc Curie temperature as a function of composition. The results suggest (a) that the Invar effect is quenched in these ultrathin pseudomorphic fcc films of FexNi(1−x)alloys and (b) the magnetic phase of Fe atoms is the low‐spin ferromagnetic phase. The CoxNi(1−x)films show the expected monotonic decrease inTcwith increasing Ni content.