Comprehensive Studies of Magnetic Properties of Metal-Organic Frameworks and Molecular Compounds

Single-ion magnets (SIMs) are at the forefront of molecular electronic spin magnets with potential applications in magnetic memory storage devices. However, the magnetic properties of the SIMs are yet to be completely understood, especially the magnetic properties of large anisotropy systems. A part of this dissertation is to utilize optical and neutron spectroscopies such as far-IR magneto-spectroscopy (FIRMS) and inelastic neutron scattering (INS) to quantify the anisotropy and study the phonon properties of the SIMs as two-dimensional (2-D) metal-organic frameworks (MOFs) or coordination polymer (CP), and a molecular magnet. In addition, ab initio calculations are used to understand the origin of the anisotropy and the electronic structure of the systems. Furthermore, the systems studied in this dissertation can also be quantum bit (qubit) candidates. Qubits are the building blocks of quantum computers. The properties of qubits can be determined using pulsed electron paramagnetic resonance (pulsed EPR). The results yielded the spin-lattice relaxation time and the spin-spin relaxation time, where both relaxation times are crucial in determining the effectiveness of the qubit candidates. The second part of this dissertation focuses on studying the symmetry-protected topological states of a Haldane one-dimensional (1-D) spin-1 chain as a 2-D MOF. The topological properties of the Haldane spin-1 chain can be highlighted by the Haldane energy gap that exists between the non-magnetic singlet ground state and the triplet excited state, the fractionalized edge states, and the system’s robustness to external perturbations through symmetry-protection. Optical and neutron spectroscopies in addition to the magnetic susceptibility measurements were used to quantify the energy gaps as well as the anisotropy that governs the system. Furthermore, the spin chain is found to exhibit a critical field and critical temperature where the system observes a phase transition. These studies in this dissertation, in part, aim to give a complete understanding of the magnetic anisotropy and phonon properties of the SIM and qubit systems as well as to have a comprehensive understanding of the topological properties of the Haldane 1-D spin-1 chain system.