He+ ion irradiation-induced disordering in L10-FePd thin films: Ion fluence dependence

Highly ordered, epitaxial, isotope-periodic [natFePd/57FePd] multilayers were prepared by molecular beam epitaxy and irradiated with 130 keV He+ ions to fluences of up to 1.49 × 1016 atoms cm−2. Electron microscopy showed a gradual accumulation of defects and disordering in irradiated samples. A significant decrease in the long-range order parameter was observed by X-ray diffraction analysis. However, the structural changes remained local, as nuclear resonant X-ray reflectometry confirmed that the isotope multilayer maintained good periodicity.