Non-collinear magnetism in Mn monolayer on Ag(111) fcc: Density functional calculations

The magnetic properties of Mn monolayer on Ag (111) surface have been studied, using the first-principle plane-wave implementation of the density-functional theory (DFT). Several collinear and non-collinear magnetic configurations have been considered including the effects of different stacking sequences for the surface termination. We compare our results with recent experimental data of Gao et al. [C. L. Gao, W. Wulfhekel and J. Kirschner, Phys. Rev. Lett. 101, 267205 (2008)]. Our simulations reveal that the lowest energy state is antiferromagnetic, and corresponds to an out-of-plane collinear antiferromagnetic state, Néel structures when we take into account the spin-orbit interactions while the 120° antiferromagnetic Néel has an excess energy of 56.06 meV/Mn. The magnetic anisotropy energy found between the antiferro-magnetic out-of-plane and in-plane structures is of 2.65 meV. These findings are in agreement with the previous electronic structure calculations, which pointed to a collinear row-by-row antiferromagnetic ground state but in disagreement with the experimental finding. Also, our results for Mn/Ag (111) suggest that a non-collinear ground state corresponding to the clean surface can be excluded while more complex systems, including surface contamination or oxidation, should be considered to reproduce the experimental 120° Néel structure.