Energetics and the magnetic state of Mn2 adsorbed on Au(111): Dimer bond distance dependence

• The diffusion of Mn2 on Au(111) is studied for Mn–Mn distances up to 6.8 Å. Our results are consistent with formation of clusters.
• The Mn atoms have a anti-parallel coupling for almost all distances, in agreement with RKKY.
• For a particular geometry the Mn2 have a ferromagnetic coupling, probably a double exchange mechanism.

In this work we present a theoretical study of the adsorption Mn2 dimer on the Au(111) surface. Here we use the density functional theory to construct a map of adsorption energies, EA, of Mn2 on a Au(111) surface as a function of interatomic bond distance, dMn–MndMn–Mn, among Mn atoms. We employed a 4×4 supercell of Au(111) surface which lead us to reach dMn–MndMn–Mn values in the range from 2.6 to 6.8 Å. To make a full study of the adsorption energies we considered the antiferromagnetic (AFM) and ferromagnetic (FM) states of the Mn2 on the surface. The energy landscape contains local minima when the Mn atoms are adsorbed above triangular sites and barriers that the Mn adatoms have to overcome when they move across the Au(111) surface along various paths. Our results show that the lowest energy state corresponds to the state in which the Mn atoms are next-nearest neighbors and are antiferromagnetically coupled. Furthermore, all the local minima with higher bonding energy are also those in the antiferromagnetic state. Nevertheless we find a short interval in which the FM state has lower energy than the AFM one. Finally, scanning tunneling microscope simulations for various dimer configurations on surface are reported.