Nanospintronics with Molecular Magnets - Tunneling and Spin-Electric Coupling

This dissertation investigates theoretically electric control of the magnetic properties of molecular magnets. Two classes of magnetic molecules are considered. The first class consists of molecules that are spin frustrated. As a consequence of the frustration, the ground-state manifold of these molecules is characterized by states of different spin chirality, which can be coupled by an external electric field. Electric control of these spin states can be used to encode and manipulate quantum information. The second class comprises molecules known as single-molecule magnets, which are characterized by a high spin and a large magnetic anisotropy. Here the main goal is to control and manipulate the magnetic properties, such as the anisotropy barriers, by adding and subtracting individual electrons, as achieved in tunneling transport. Papers I, II and III deal with spin-electric coupling in spin frustrated molecules. Spin density functional theory is used to evaluate the parameters that control the strength of this coupling. Paper I reports the electronic and magnetic properties of the triangular antiferromagnet Cu3. It is found that an external electric field couples to the spin chirality of the system. The strength of this coupling is large enough to allow efficient spin-electric manipulation with electric fields generated by a scanning tunneling microscope. Paper II investigates the zero-field splitting in the ground-state manifold of the triangular Cu3 molecular magnet caused by the Dzyaloshinskii-Moriya (DM) interaction. It employs a Hubbard model approach to elucidate the connection between the spin-orbit and the DM interaction. It is shown that the DM interaction constant D can be expressed in terms of the microscopic Hubbard-model parameters, which are calculated by first principles methods. Paper III investigates systematically the spin-electric coupling in several triangular molecular magnets, such as V3 and Cu3O, and its dependence on different types of magn