UC Berkeley

This dissertation describes chemical strategies for the development of novel dynamic spin systems. Using synthetic molecular design principles, three metal–organic coordination solids were created for specific applications in spin dynamics. These targets range from diluted qubit arrays, where the dynamics of isolated spins are of consequence; to magnetic materials that order at room temperature for magnonic applications; to geometrically frustrated, layered 2D materials, which display novel emergent properties.Chapter 1 presents an overview of spin dynamics, from weakly interacting to strongly interacting spin ensembles. First, the manipulation of individual spins using microwave photons is addressed, and key figures of merit for coherent qubits are discussed. Second, the basics of spin- waves, and their quantum analog, the magnon, are introduced. Similarities between high performance magnonic materials are considered. Finally, frustrated magnetic materials, both positionally disordered and geometrically frustrated, are presented. Magnetic materials housing spin glass phases, which undergo an unusual phase transition that preserves certain spin dynamics, are emphasized. Chapter 2 describes the synthesis and characterization of a nanoporous metal–organic framework containing diluted trivalent cerium. Due to the low density of nuclear spins in this framework, the cerium functions as a qubit, comparing favorably to solid-state cerium analogs. As a demonstration of the possibilities of quantum sensing in such a system, the coherent dynamics of the system are compared when the pores are voided, versus filled with several different solvents. As the distance between pore dwelling analytes and the qubit is small, hyperfine interactions are readily observed through various relaxometry and hole-burning techniques. Chapter 3 describes the electrosynthesis and deposition of thin films of the amorphous magnonic material vanadium tetracyanoethylene, V(TCNE)2. This novel synthetic method allows for facile synthesis of a material that is otherwise prohibitively challenging to make. Electrodeposition allows for this material to be deposited on conductive substrates using simple starting materials. The spin-wave characteristics of the material are studied, and are shown to be competitive with other high performance magnonic materials. Chapter 4 describes the synthesis and characterization of the novel layered metal–organic coordination solid Mn3C6S6. The 2D sheets comprising this material are kagome lattices, a classic platform for the study of geometric spin frustration. Extensive magnetic characterization shows that this material is a “topological” spin glass, with accordingly exotic dynamic behavior. Upon field annealing, the material displays exchange bias, defined as a shift in the hysteretic loop. This exchange bias can be induced isothermally, suggesting that a novel mechanism is responsible. Field dependent chiral domain wall defect modes are presented as a likely rationale for the observed exchange bias.