We have performed ab initio density functional theory calculations to investigate the formation energy and the effects of low dimensionality and reduced coordination on the magnetic properties of pseudomorphically grown monolayers of Co-Ag surface alloys on a Rh(111) substrate. We find that if such an alloy could form, its magnetic moment would be considerably enhanced relative to that of bulk Co. However, we also find that its formation is energetically disfavoured against phase-segregated forms; this can be mainly attributed to the high `chemical’ cost of forming Ag-Co bonds. Trends in the variation of magnetic moment with alloy composition are largely consistent with the Stoner argument.
