Electric-field control of spin orientation of manganocene: An insight into molecule-substrate interactions.

The manipulation of spin orientations in molecular nanomagnets assembled on surfaces is essential for the development of memory devices. These properties are dominated by interactions with the substrate. Here, we show that individual manganocene molecules deposited on Cu(111) exhibit different easy magnetization directions in an applied electric-field due to different contact geometries. Using Hubbard-U corrected density-functional theory to describe strong correlation effects and a non-self-consistent diagonalization method to treat spin-orbit coupling, we demonstrate that the field-induced spin reorientation transition occurs in the standing-up molecule in both high-spin (HS) and low-spin states, while the transition only occurs in the HS state for the flat-lying molecule. We propose plausible mechanisms in terms of charge polarization at the interface as well as modifications of the electronic states near the Fermi level E F. We show that the molecule largely preserves its arrangement of 3d orbitals in the standing configuration due to the "insulating layer" (bridging ligand), whereas direct contact of the Mn ion with the substrate in the lying configuration induces an orbital degeneracy around E F, thus preventing the electrical modulation of magnetic anisotropies.