Evolution of the magnetic hyperfine field profiles in ion-irradiated Fe60Al40 film measured by nuclear resonant reflectivity

Nuclear resonant reflectivity (NRR) from an Fe60Al40 film was measured using synchrotron radiation at several grazing angles near the critical angle of the total external reflection. By laterally resolved measurements after 20 keV Ne+ ion irradiation with gradually varied fluences of 0 - 3.0 x 10^14 ions/cm2, the progressive creation of the ferromagnetic A2 phase with increasing ion fluence was confirmed. The observed depth-selectivity of the method has been explained by application of the standing wave approach. From the time spectra of the nuclear resonant scattering in forward or diffraction directions the depth-profiles for different hyperfine fields were extracted. The results evidence that the highest magnetic hyperfine fields (~ 18 % 23 T) are initially created at the center part of the film and partially at the bottom interface with SiO2 substrate. The evolution of the ferromagnetic onset, commencing at a fixed depth within the film and propagating towards the interfaces has been directly observed. At higher fluence (3.01014 ions/cm2) the depth distribution of the ferromagnetic fractions became more homogeneous across the film depth in accordance with previous results.