Structural and magnetic properties of CoRh nanoparticles

The structural and magnetic properties of free-standing ConRhm clusters (N=n+m≈110 and n≈m) of three different symmetries—cubo-octahedral, icosahedral, and hcp—were investigated in two different chemical orders: segregated and alternated layering alloyed. The initial geometrical structures constructed at bulk distances were relaxed with a many-body Gupta potential to obtain the cluster geometries and energies. We find that the lowest energy in the different structures in all the cases corresponds to the segregated case (Rh-rich core surrounded by Co shells), and that the lowest energy is associated with the hcp structure. The interatomic distance for all the structures is slightly lower than the Rh bulk distance, in good agreement with the experimental observation , [Zitoun , Phys. Rev. Lett. 89, 037203 (2002)]. The spin-polarized electronic structure and related magnetic properties of these optimized geometries were calculated by solving self-consistently a spd tight-binding Hamiltonian. The magnetic moment of the Rh atoms shows a strong dependence on the position and environment, whereas the Co atoms show a smoother dependence. The magnetic moment of the Rh (Co) atoms in the alloying case are larger (lower) than the ones in the segregated case, however, the overall average for the segregated and alloying case are only slightly different for the different structures. The results are compared with the experimental data and with other theoretical calculations available in the literature.