UC San Diego

The focus of this dissertation is the thorough analysis of the effects of dipolar coupling on magnetic relaxation behavior within erbium-based molecular magnets. Utilizing the Er-COT unit as the starting point and building block, we investigate intra- and inter-molecular dipolar coupling motifs generated with analogous highly anisotropic building block units. Each chapter holds a specific focus, organized as follows: Chapter 1 offers a brief introduction to molecular magnetism, followed by an overview of topics necessary towards understanding magnetic relaxation in the scope of this work, including energy perturbations, relaxation dynamics, and anisotropy; an introduction to the Er-COT unit and coupling schemes in lanthanide-based molecular magnetism, and the motivation for investigating dipolar coupled systems. The chapter concludes with extended chapter summaries for the remainder of this work. Chapter 2 focuses on the role and effects of intramolecular dipolar coupling in a series of compounds of increasing nuclearity. This work demonstrates the ability of intramolecular dipolar coupling to control quantum tunnelling of magnetization, and thus the rate and mechanism of magnetic relaxation. This chapter utilizes an expanded frequency space magnetometry technique to garner new insights into magnetic relaxation by visualizing, fitting, and analyzing multiple relaxation regimes. The chapter concludes with an intuitive model of thought based on a simple vector addition model, within which spin interactions can be estimated directly from a crystal structure. Chapter 3 discusses the effects of intermolecular dipolar coupling within a series of identical single-ion magnets within varied crystal packing environments. This work depicts the propensity of intermolecular dipolar coupling to drive dramatic differences in resulting magnetic behavior and seeks to shed light on the relationship between single-ion magnetism and solid-state magnetism. This chapter applies a novel fitting methodology to quantify additional parameters from isothermal magnetization data for downstream analysis. Chapter 4 presents the analysis of a highly symmetric, near-tetrahedral tetranuclear single-molecule magnet to discuss the effects of crystallographic symmetry on the resulting dipole-coupled spin-space symmetry. This chapter discusses the ensuing available rhombic dodecahedral quantum space of this molecule, composed of octahedral and cubic subspaces, and makes connections to theoretically proposed quantum Cayley networks upon hypercubes.