  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 studied the MA of
transition metal dimers Co-Os, Co-Co and Os-Os adsorbed on two-dimensional
ferroelectric In2Se3 (In2Se3-CoOs, In2Se3-OsCo, In2Se3-CoCo and In2Se3-OsOs) by
first-principles calculations. It is found that the Co-Os dimer in In2Se3-CoOs
has large total perpendicular magnetic anisotropy energy (MAE) of ~ 40 meV. In
particular, the MAE arising from Os atom is up to ~ 60 meV. The large MAE is
attributed to the high spin-orbit coupling constant and the onefold
coordination of Os atom. In addition, the MA of the dimers can be tuned by the
polarization reversal of In2Se3. When the polarization is upward, the easy-axis
directions of MA in In2Se3-OsCo, In2Se3-CoCo and In2Se3-OsOs are all in-plane,
while the directions become perpendicular as the polarization is switched to
downward. For the In2Se3-CoOs, switching polarization from upward to downward
enhance the perpendicular MA from ~ 20 meV to ~ 40 meV. Based on the
second-order perturbation theory, we confirm that the exchange splitting of
dxy/dx2-y2 and dxz/dyz orbitals as well as the occupation of dz2 orbital at the
vicinity of Fermi level play important roles in the changes of MA with the
reversal of FE polarization of In2Se3.
