Significant charge transfer between a single-molecule magnet Mn12 and a Bi substrate

Abstract

We investigate electronic and magnetic properties of a single-molecule magnet Mn12 adsorbed on Bi(111) without any linker molecules, using a first-principles method. This study is motivated by a scanning tunneling microscopy experiment on individual Mn12 molecules on a Bi substrate. We apply density-functional theory including spin–orbit coupling, on-site Coulomb repulsion U, and dipole corrections. With geometry relaxation, the Mn12 molecule remains slightly tilted relative to the surface such that its magnetic easy axis is 6° away from the axis normal to the surface. Upon adsorption, a gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the Mn12, is reduced to 0.43eV, compared to the corresponding gap of 1.07eV for an isolated Mn12. The total magnetic moment of the adsorbed Mn12 increases to 21μB. This is due to charge transfer from the Bi slab to the Mn12. The tilted geometry of the Mn12 allows to favor one of the outer Mn sites for charge transfer and magnetic moment change. Although bulk Bi is semimetal, there are surface states near the Fermi level, which facilitates significant charge transfer and a change in the magnetic moment.