Theory of the electronic and magnetic structure and transport properties of single molecule magnets

Developing electronic components at the molecular scale is the ultimate goal in molecular electronics. Because of their large magnetic anisotropy barriers and associated stable magnetic moments, single molecule magnets (SMMs) bring a new dimension to this field and also raise the possibility of molecular magnetic information storage and quantum computation. Therefore the transport properties of transistors based on individual SMMs are attracting considerable experimental and theoretical interest at present. This thesis presents a theoretical investigation of the electron and spin transport and associated phenomena in SMM transistors (SMMTs). A tight binding model is developed as an alternative approach to the giant spin Hamiltonian and density functional theory (DFT) methodologies for studying SMMs. Unique aspects of this approach are that it captures more physics than the giant spin Hamiltonians do but is much simpler than DFT and it has more flexibility for modeling experimental behaviors. Because of its simplicity this model is helpful in developing a physical understanding of SMMs and their transport properties. The tight binding model yields the total Mn12 SMM spin, the spins of the individual Mn ions, the magnetic easy axis orientation, the size of the magnetic anisotropy barrier and the size of the HOMO-LUMO gap consistent with experiments. Based on this tight binding methodology, this thesis addresses the following transport problems of current interest: ligand-based transport resonances in SMMTs, gate controlled switching between Coulomb blockade and coherent resonant tunneling in SMMTs, identification of the orientation of the magnetic easy axis of a SMM, the spin filtering effect of the SMMTs, quantum dot spin valves based on SMMs which support ligand--based transport, and tunneling and cotunneling transport through Mn12 SMMs in the weak coupling regime.