Present study compares the effects of 200 MeV Ag15+ and 100 MeV O7+ ion irradiations on the structural, interfacial mixing and magnetic properties of annealed Pt/Co/Pt layers fabricated by DC magnetron sputtering. X-ray diffraction analysis shows that ion irradiations coupled with post annealing results in the formation of the face centred tetragonal L1(0) CoPt phase. Irradiation using 200 MeV Ag15+ ions having higher ionizing energy transfer to the film was found to be more efficient in causing structural phase transition as compared with that using 100 MeV energy O7+ ions having lower ionizing energy transfer at similar fluence. Rutherford back scattering analysis reveals the role of defect mediated inter-atomic diffusion in tailoring the alloy composition of the film irradiated by different energetic ions. A broad magnetic switching field distribution for O7+ ion irradiated films compared to Ag15+ ion irradiation was evident from the magnetic measurements. The contribution of alloy composition to switching field distribution has been discussed in details. Above results showed that the electronic energy loss and fluence dependent defects, generated by irradiation, played an important role in tuning the structural, atomic diffusion and magnetic reversal properties of Pt/Co/Pt. (C) 2014 Elsevier B.V. All rights reserved.