Low Energy Excitations in Spin Clusters and Molecular Solids

This thesis investigates low energy magnetic and vibrational excitations in molecular solids. Analytical and numerical studies of these two types of excitations, both in idealized systems and in more complicated models that are thought to capture the relevant physics of several materials. The materials considered include molecular magnets and layered organic superconductors and semiconductors. Our results include exact expressions for certain magnetic observables, neutron scattering structure factors for small spin 1/2 clusters, studies of the molecular dynamics of Fe₈Br₈ molecular magnet, the e®ects of symmetry breaking in (DT-TTF)₂Au(mnt)₂ spin ladder candidate, and the importance of totally symmetric modes in κ-ET-based superconductors with reduced symmetries. Finally, a preliminary study of the interaction of magnetic and vibrational excitations in a model coupled Hamiltonian is discussed, which illustrates spin-vibrational effects that may be observable in future studies of magnetic materials.