First-principles theory of ultrathin magnetic films

We report on a set of systematic first-principles electronic structure inve stigations of the magnetic spin moments, the magnetic spin configurations, and the magnetic coupling of ultrathin magnetic films on (001)- and (Ill)-o riented noble-metal substrates and on the Fe(001) substrate. Magnetism is f ound for 3d-, 4d-, and Sd-transition-metal monolayers on noble-metal substr ates. For V, Cr, and Mn on (001) substrates a c(2 x 2) antiferromagnetic su perstructure has the lowest energy, and Fe, Co, Ni are ferromagnetic. On(ll l) substrates, for Cr the energy minimum is found for a 120 degrees non-col linear magnetic configuration in a (root 3 x root 3)R30 degrees unit cell, and for Mn a row-wise antiferromagnetic structure is found. On Fe(001), V a nd Cr monolayers prefer the layered antiferromagnetic coupling, and Fe, Co, and Ni monolayers favour the ferromagnetic coupling to Fe(001). The magnet ic structure of Mn on Fe(001) is a difficult case: at least two competing m agnetic states are found within an energy of 7 meV. The Cr/Fe(001) system i s discussed in more detail as the surface-alloy formation is investigated, and this system is used as a test case to compare theoretical and experimen tal scanning tunnelling spectroscopy (STS) results. The possibility of reso lving magnetic structures by STS is explored. The results are based on the local spin-density approximation and the generalized gradient approximation to the density functional theory. The calculations are carried out with th e full-potential linearized augmented-plane-wave method in film geometry.