Investigation of the origin of the decrease in exchange biasing in Ga⁺ ion irradiated CoFe/IrMn films

Irradiation of CoFe/IrMn exchange biased bilayers by 30 keV Ga<sup>+</sup> ions leads to a reduction in the exchange biasing. Here we have used various imaging and analytical techniques including high resolution transmission electron microscopy and spectrum imaging based on electron energy-loss spectroscopy to determine how the physical structure of the multilayer changes as a function of irradiation dose. Element mixing across the interfaces is found to be the most important effect although significant grain growth is also observed. Computer simulation, incorporating the effects of collision cascades, can largely account for the experimental observations. The ways in which these changes lead to modification of the magnetic properties are discussed