Alteration of exchange anisotropy and magnetoresistance in Co/Cu/Co/FeMn spin valves by ion bombardment

The dose dependence of the exchange bias field and magnetoresistance by 10 keV-He ion bombardment in an applied magnetic field were investigated for Co/Cu/Co/FeMn top spin valves. The exchange bias field H-eb of the pinned Co layer can be enhanced, reversed, and reduced similarly to an exchange biased bilayer system. Additionally, upon ion bombardment, the free Co layer couples increasingly strong to the pinned Co layer until they act magnetically as one single pinned layer. The magnetoresistance decreases exponentially with increasing ion dose, caused by a higher sheet resistance due to increasing defect density and increasing coupling between the free and the pinned ferromagnetic layer. A phenomenological model is extended to describe the ion bombardment-induced changes of H-eb of ferromagnet/antiferromagnet exchange biased bilayers by including saturation effects. This model is compared to available experimental data. (C) 2003 American Institute of Physics.