Magnetism in Rh monolayers

Abstract

We have studied the magnetic behavior of a 4$d$ transition metal Rh monolayer (ML) on different substrates (Ag, Au, Cu) and orientations. We find the Rh monolayer to be magnetic in the (001) orientation on all the substrates, in the (111) direction for Au and Ag alone ($\mu \approx 0.6$ $% \mu _{B}$) for both, in the (110) one we do not find any magnetic activity. We analyze the parameters that have been suggested as general criteria for magnetism in the monolayer-substrate system. In particular, we study several possible geometric parameters and the bandwidth as possible clues to predict the magnetic behavior. A detailed analysis shows that the physics underlying the switching on of magnetism in a Rh-ML on noble metal substrates, is determined by an intraband transfer of $d$-electronic states (as compared to the Rh surface), from lower and higher energies to the Fermi level. This effect enhances the density of states at that energy, in an important way and shrinks the $d$-bandwidth. It seems to depend strongly on specificities of the interaction between the ML and the substrate that are hardly taken into account by a single parameter, in a general way. We impose charge neutrality in our calculations but deal explicitly with the changes to be expected if charge transfer would actually occur.