Large perpendicular magnetic anisotropy of transition metal dimers driven by polarization switching of a two-dimensional ferroelectric InSe substrate.

Large perpendicular magnetic anisotropy (MA) is highly desirable for realizing atomic-scale magnetic data storage which represents the ultimate limit of the density of magnetic recording. In this work, we study the MA of transition metal dimers Co-Os, Co-Co and Os-Os adsorbed on two-dimensional ferroelectric InSe (InSe-CoOs, InSe-OsCo, InSe-CoCo and InSe-OsOs) using first-principles calculations. We find that the Co-Os dimer in InSe-CoOs has a total magnetic anisotropy energy (MAE) of ∼40 meV. The MAE arising from the Os atom in InSe-CoOs is up to ∼60 meV. Such large MAE is attributed to the high spin-orbit coupling constant and the onefold coordination of the Os atom. In addition, perpendicular MA can be enhanced in InSe-CoOs and induced in InSe-OsCo, InSe-CoCo and InSe-OsOs by the ferroelectric polarization reversal of InSe. We demonstrate that the enlargement of exchange splitting of d/d and d/d orbitals for Os atoms in InSe-OsOs, Co atom in InSe-CoOs and Os and Co atoms in InSe-OsCo is responsible for the increase of MAE; while, for the upper Co atom in InSe-CoCo and the Os atom in InSe-CoOs, the energy rise of the d orbital owing to the change of the crystal field effect by the reversal of ferroelectric polarization results in the increase of MAE.