First-Principle Studies of Spin-Electric Coupling in a Cu3 Single Molecular Magnet

摘要

We report on a study of the electronic and magnetic properties of the triangular antiferromagnetic (Cu3) single-molecule magnet, based on spin density functional theory. Our calculations show that the low-energy magnetic properties are correctly described by an effective three-site spin s = 1/2 Heisenberg model, with an antiferromagnetic exchange coupling J approximately equal to 5 meV. The ground state manifold of the model is composed of two degenerate spin S = 1/2 doublets of opposite chirality. Due to lack of inversion symmetry in the molecule these two states are coupled by an external electric field, even when spin-orbit interaction is absent. The spin-electric coupling can be viewed as originating from a modified exchange constant delta-J induced by the electric field. We find that the calculated transition rate between the chiral states yields an effective electric dipole moment d = 3.38 x 10(exp -33)C m approximately equal to e10(exp -)4a, where a is the Cu separation. For external electric fields epsilon approximately equal to 10(exp 8) V/m this value corresponds to a Rabi time tau approximately equal to 1 nanosecond and to a delta-J of the order of a few micro-eV.