Electronic and magnetic properties of bimetallic L1$_0$ cuboctahedral clusters by means of a fully relativistic density functional based calculations

By means of density functional theory (DFT) and the generalized gradient approximation (GGA) we present a structural, electronic and magnetic study of FePt, CoPt, FeAu and FePd based L1$_0$ ordered cuboctahedral nanoparticles, with total numbers of atoms, N$_{tot}$ = 13, 55, 147. After a conjugate gradient relaxation, the nanoparticles retain their L1$_0$ symmetry, but the small displacements of the atomic positions tune the electronic and magnetic properties. The value of the total magnetic moment stabilizes as the size increases. We also show that the Magnetic Anisotropy Energy (MAE) depends on the size as well as the position of the Fe-atomic planes in the clusters. We address the influence on the MAE of the surface shape, finding a small in-plane MAE for (Fe,Co)$_{24}$Pt$_{31}$ nanoparticles.