Calculation of magnetic and structural properties of small Co–Rh clusters

Structural and magnetic properties of CoMRhN clusters with M+N⩽4 atoms are determined by performing first-principles calculations in the framework of the density functional theory in a generalized gradient-corrected approximation and within the projector-augmented wave method. The role of magnetism on the most stable structures and on the energy differences among the low-lying isomers is quantified by comparing magnetic and non-magnetic solutions of the Kohn–Sham equations. As usual in small clusters, CoMRhN clusters show contracted interatomic distances with respect to the bulk. They exhibit ferromagnetic-like order with environment-dependent local magnetic moments μ(i). The average magnetic moments per atom μ̄(M,N) and μ(i) are generally more than a factor 2 larger than in macroscopic alloys of similar concentration. For a given cluster size M+N, μ̄ increases with increasing number of Co atoms M. The μ(i) at Rh atoms are remarkably enhanced by the presence of Co nearest neighbors, while the μ(i) at Co atoms are not much affected by the presence of Rh atoms. The correlation between structure, chemical order, and environment-dependent magnetic properties is discussed.