Evolution of magnetic domain structure formed by ion-irradiation of B2-Fe0.6Al0.4

Magnetic domains and magnetization reversal in 40 nm thick films of Fe0.6Al0.4, 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.