An applied field is used to perform Ga+ ion irradiation on a CoFe/PtMn bilayer.Effects of the applied field and energy transfer between Ga+ ions and antiferromagnetic(AFM) atoms on the exchange bias field Hex are investigated.A partially reversed Hex is found in CoFe/PtMn specimens irradiated at a dose of 1 × 1014 ions/cm2 with an applied field anti-parallel to the original exchange bias direction.We believe that the rapid energy transfer and local temperature increase originating from the interaction between Ga+ ions and AFM atoms result in spin reversal and the formation of reversed AFM domains when specimens are irradiated with anti-parallel fields.The decrease in Hex when annealing the film in a negative saturation field indicates a thermal decay process.The AFM moments are reversed by thermal activation over an energy barrier distribution,which may change in some way as the temperature increases.