“…Ion beam mixing carried out on Co/Pt mulilayers [16] and bilayers [17] has resulted in CoPt and CoPt 3 phase synthesis. We have reported the formation of ordered CoPt phase by carrying out ion beam mixing in Pt/Co/Si bilayer films [18] and we have also demonstrated that the ion beam mixing in the Pt/Co/Si bilayers using Pt + ions is diffusion controlled rather than reaction controlled [19]. In this paper, we suggest a mechanism of phase formation during ion beam mixing in Pt/Co/Si(substrate) bilayers.…”