In the Fe–Mo system, amorphous alloys are thermodynamically unstable and are hard to form in the bulk state. In multilayered films, however, amorphous alloys were produced by room temperature 200 keV xenon ion mixing. It was found, when keeping the total thickness of the multilayered film constant at 40 nm, that the composition range favoring amorphization extended from the equiatomic stoichiometry towards the two metal sides with increasing number of metal layers. This alloying behavior is discussed in terms of a simple thermodynamic calculation. ©1997 American Institute of Physics.