Electronic Structure and Magnetism in Sm(Co,Cu)₇

The electronic density of states, spin-splittings and atomic magnetic moments of SmCo_7-xCu_x are studied by means of the spin-polarized multi-scattering X_α method. The results show that a few of the electrons can transfer to the Sm 5d^0 orbital due to orbital hybridization between Sm and Co. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore result in the long-range ferromagnetic order in SmCo_7-xCu_x. The Curie temperature of SmCo_7-xCu_x is generally lower than that of the corresponding pure Co, which may be explained by the weaker average strength of coupling between Co lattices due to some negative exchange couplings mainly from the 2e site. The calculated results for the Sm₅Co₃₀Cu₄ cluster may lead to a better understanding of why SmCo_7-xCu_x is stable phase. Since the negative coupling of the 2e sites becomes small and the d bond at E_F becomes stronger in contrast to SmCo₇, which results in decrease of the free energy of the system, the stable ferromagnetic order forms in SmCo_7-xCu_x.