Chemical order and magnetic properties in small Mx−2N2 nanoalloys

A systematic analysis of the chemical order, structure stability and magnetic behaviour of small transition metal binary nanoalloys is performed employing spin-polarised ab-initio simulations. The doping of icosahedral geometries at 13 and 19 atoms of magnetic materials with two impurities both magnetic (Fe, Co, Ni, Pt) and non-magnetic (Ag, Cu) is considered. In CoFe, the most favourable substitutional sites are those which maximise the total magnetic moment of the system: Fe dopants tend to occupy surface sites while Co atoms stay in the inner. For all the other nanoalloys, the doping sites respect a chemical order that leads to a surface energy minimization often followed by a depression of the total magnetization. The ferromagnetic arrangement is always the energetically most favourable order apart from the Ag-doped case where the anti-ferromagnetic alignment is almost degenerate to the ferromagnetic phase.