Dynamical Valence Fluctuations and Magnetic Anisotropy in Sm(Co,Cu) 5

The magnetic properties of Sm-based intermetallics are governed by a delicate interplay between localized 4f states, exchange interactions, and valence fluctuations, yet the role of dynamical 4f correlations remains poorly understood. Here we investigate the electronic structure and magnetic anisotropy of SmCo 5 and SmCu 5 using self-consistent DFT+ U (ED), which explicitly treats dynamical fluctuations of the Sm 4f shell. We find that SmCo 5 exhibits pronounced Sm 2+ --Sm 3+ valence fluctuations, with the 4f ground state dominated by f 5 and f 6 configurations. The resulting dynamical 4f correlations yield near compensation of the Sm spin and orbital moments and provide a quantitative description of the electronic structure, magnetic moments, and large uniaxial magnetic anisotropy of SmCo 5. Upon replacing Co with Cu, the balance shifts toward the f 6 configuration, with substantial changes in the Sm spin and orbital moments. In SmCu 5, this evolution of the 4f configuration is accompanied by a pronounced reduction of both the total magnetic moment and magnetic anisotropy. These results demonstrate that dynamical 4f valence fluctuations are essential for understanding the contrasting magnetic properties of SmCo 5 and SmCu 5 and provide a microscopic framework for describing magnetic anisotropy upon Co to Cu substitution in Sm(Co,Cu) 5.