Spin-polarization properties and electronic structure of the ordered c(2 x 2) MnCu/Cu(110) surface alloy

The spin-ordering and electronic properties of the c(2 x 2) MnCu/Cu(1 1 0) surface alloy are investigated by means of ab initio density-functional calculations. We first address the magnetic ground state and the robustness of the spin-polarization properties. The lowest-energy state is found to be ferromagnetic with a very low Curie temperature, showing that the paramagnetic phase should be established in this system at room temperature. The calculated trends obtained for the various spin structures considered indicate that the local Mn-spin moment and resulting reduced work function as well as Mn-outward buckling should persist in the paramagnetic phase. We then address the electronic surface-band structure of the paramagnetic phase close to the Fermi energy, in connection with the interpretation of recent angle-resolved-photoemission-spectroscopy experiments at room temperature. Our calculations account for an intriguing new surface-band feature observed experimentally near the (X) over bar point upon alloy formation, and provide a microscopic interpretation for this feature and for the alloy-induced changes in the Cu(1 1 0) Shockley surface state.