First-principle calculations of the electronic structure and the magnetism of the rare earth metal Sm monolayer

The electronic structure and the magnetism of fcc Sm(001) and hcp Sm(0001) monolayers are investigated using the all-electron total-energy full-potential linearized augmented plane-wave (FLAPW) method, emphasizing the valence of the Sm monolayers (MLs). The valences are found to be 2.47 and 2.49 for paramagnetic fcc Sm(001) and hcp Sm(0001) MLs, respectively. The spin-polarization affects the valence so that the valence of the ferromagnetic hcp Sm(0001) ML becomes 2.33, which is less than that of paramagnetic hcp Sm(0001) by 0.16. The contribution of the valence electrons to spin magnetic moment is 0.45 mu(B), which comes in part from spontaneous polarization (estimated to be 0.29 mu(B)) and in part from induced polarization due to the exchange interaction between the valence electrons and the f-electrons. The paramagnetic bands are rigidly split into spin-up and spin-down bands when spin polarization is considered.