Modifications of structural, compositional, and magnetic properties of ultrathin Fe/Si bilayer films induced by Ar+ ion bombardment have been studied. The films were grown at room temperature using an electron beam evaporation system. After evaporation, the samples were bombarded with 3 keV Ar+ ions at fluences around 4 x 10(15) ions/cm(2). The self-organization of the Fe nanostructures and the subsequent change in morphology due to the Ar+ bombardment were studied using atomic force microscopy. The structural changes were investigated using grazing incidence x-ray diffractometer. Furthermore, the changes in magnetization and magnetic orientation were studied using vibrating sample magnetometer. It is seen that the Ar+ ion bombardment tends to rotate the easy axis of magnetization of the Fe/Si bilayer film. The results also indicate significant change in structural characteristics, indicating that ion bombardment can be used as an efficient technique of tuning the magnetic properties of ultrathin magnetic films. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3457935]