We report on the effects of 2 MeV He+-ion irradiation on the magnetic and structural properties of Pt/Cr/Co multilayers. We observe He+-ion irradiation leads to mixing across the interfaces [Pt (2.5 nm)/Cr (0.8 nm)/Co (3.0 nm)] × 6/Si multilayers. In addition, we observe Co-Cr-Pt phase formation at the highest fluence of 5.5 × 1016 ions cm-2. This is accompanied by an enhancement in the coercivity. Such enhancement in the coercivity is attributed to inhomogeneous alloying and a possible mixing-induced strain. High-resolution transmission electron microscopy confirms the formation of CoCrPt ternary alloy phase. These findings are explained in the light of ion beam induced recoil mixing and ionization events. © 2009 Elsevier B.V. All rights reserved.