Magnetic domains and magnetization reversal in 40 nm thick films of Fe 0.6 Al 0.4 , have been studied by longitudinal magneto-optical Kerr effect. By varying the Ne + ion-energy E between 2 and 30 keV (keeping a constant fluence), we varied the depth-penetration of the ions, and thereby influenced the homogeneity of the induced saturation magnetization M s. The dependence of coercivity on ion energy shows maximum for 5 keV Ne +. Considerable differences in the magnetic domain formation and magnetization reversal processes were observed: at low E (≤ 5keV), the reversal process is dominated by domain nucleation mechanism (high density of domain nucleation sites), consistent with the occurrence of an inhomogeneous M s. Films irradiated with E > 5keV ions exhibit significantly low domain nucleation density, and the reversal is dominated by domain propagation mechanism, suggesting homogeneity in induced M s. These results demonstrate the tunability of magnetization reversal behavior in materials possessing disorder induced magnetic phase transitions., and T. Gemming, " Tailoring of magnetism in Pt/Co/Pt ultrathin films by ion irradiation, " Phys. Rev. B 85(5), 054427 (2012). 5.-and current-induced domain-wall motion in permalloy nanowires with magnetic soft spots, " Appl. Phys. Lett. 98(20), 202501 (2011). 7. D. McGrouther and J. N. Chapman, " Nanopatterning of a thin ferromagnetic CoFe film by focused-ion-beam irradiation, " Appl. Phys. Lett. 87(2), 022507 (2005). 8. J. McCord, L. Schultz, and J. Fassbender, " Hybrid soft-magnetic lateral exchange spring films prepared by ion irradiation, " J. Sort, and J. Nogués, " Direct magnetic patterning due to the generation of ferromagnetism by selective ion irradiation of