Abstract Ion beam sputtering (IBS) was used to prepare Co/Cu multilayer films within the first antiferromagnetic coupling range. Several preparation conditions were varied to optimize the giant magnetoresistance effect. We report the improvement of magnetoresistance by changing the sputtering gas from Ar to Xe, by finding an optimal substrate position and ion beam acceleration voltage, and by increasing the growth rate. A maximum magnetoresistance of 51% was achieved at room temperature in a stack with only 16 periods. The obtained improvements compared to previous efforts are discussed in terms of interface sharpness, layer homogeneity, and impurity incorporation. The main advantage of the established plasma sputtering technique, which still yields somewhat better results compared to IBS, appears to be a larger growth rate resulting in less impurity incorporation.