The amorphization of an Fe‐Zr multilayer film due to ion‐beam mixing with protons and due to solid‐state reaction is studied in detail using backscatter Mo¨ssbauer spectroscopy, x‐ray diffraction, and Auger electron spectroscopy. The local structure of the amorphous phase produced by both processes is found to be very similar based on the Mo¨ssbauer results. The dose dependence of the ion‐beam‐mixed phase fraction can be accounted for approximately by a collision cascade mixing model. Incomplete amorphization of the Fe was observed as a result of the proton irradiation with a large enough dose to produce apparent saturation whereas complete amorphization occurred for the identical multilayer structure via solid‐state reaction. The latter was characterized by a thermal activation energy of 0.7 eV.