(Georgia Institute of Technology, 2020-03-16)
Ge, Luwei
Quantum magnetism is one of the most important branches in condensed matter physics because it serves as an excellent platform to realize model quantum many-body systems which are difficult to find elsewhere. Good understanding of the nature of magnetic excitations in such systems demands both experimental and theoretical efforts. This thesis presents comprehensive studies of the magnetic properties of several 3d transition-metal oxides for which the effective spin Hamiltonian forms quasi-1D, quasi-2D or 3D lattices. Primarily relying on advances in neutron scattering instrumentation and spin-wave theory, the work carefully examines the effectiveness of the theory of weakly interacting magnons in describing the elementary magnetic excitations of these insulators. By revealing the microscopic interactions of these systems and testing the applicability of spin-wave theory quantitatively, the work also hopes to offer useful insights or guidance to future investigations, which may extend to the entire field of quantum many-body physics.