Antiferromagnetism and segregation in cuboctahedral FePt nanoparticles

Total energies and magnetic properties of unsupported cuboctahedral near-stoichiometric FePt nanoparticles with up to 561 atoms are compared by means of large scale ab initio calculations within the framework of density functional theory. The results show that for L1(0) ordered alloys, the two (0 0 1) surfaces perpendicular to the shortened c-axis are preferably covered by Pt atoms. Also, layer-wise antiferromagnetic (AF) configurations are found with practically degenerate energies for perfectly ordered structures. The latent AF tendencies are suppressed by compositional disorder in the core layers.