Date of Award
8-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
Committee Chair/Advisor
Joseph W. Kolis
Committee Member
Colin D. McMillen
Committee Member
Thao T. T. Dominy
Committee Member
Rhett C. Smith
Abstract
Geometric magnetic frustration is a term that refers to magnetic spins that are “confused” or frustrated due to geometric arrangements of magnetic ions that prohibit the spins from magnetically ordering. This phenomenon has been subject to much research due to the ability to study exotic magnetic states and expand upon knowledge that would allow for materials to be implemented into quantum computing, memory storage and advanced sensor processing. One of the most exotic magnetic states, quantum spin liquids (QSL), has never been achieved but shows much promise. In the QSL state, magnetic spins do not order down to 0 K but have strong magnetic correlations. While this proposed state has perplexed scientists for decades, one understudied magnetic coupling pathway, Haldane coupling, has generated QSL like ground states sparking much interest and forming one of the foundations of this project. Dr. Duncan Haldane, a Nobel prize winner for this work, stated that an odd whole integer spin system (i.e. S = 1) arranged in a 1-D chain would behave nonclassically under applied magnetic fields. He theorized that spins under applied magnetic fields would couple antiferromagnetically and eventually fractionalize to then couple to their next nearest neighbor creating delocalized spin pairing and a resultant spin gap. Since this was proposed in the 1980’s only fifteen examples have been confirmed to be Haldane materials, primarily consisting of chains of metal coordination complexes, along with a few inorganic structures, one of which was from the Kolis group.
In hope to expand the study of Haldane interactions in inorganic systems, the high temperature hydrothermal synthetic method was employed due to the techniques ability to solubilize high refractory oxides at temperatures (500 – 600 ˚C) that are much lower than traditional solid state preparative methods. The high temperature hydrothermal method also allows for the growth of high quality sizeable single crystals. Because all reactions are carried out in welded silver tubing there are no reactor impurities present as is sometimes the case in other flux and melt growth techniques. Additionally, the sizeable crystals allow for anisotropic physical properties measurements to be performed which is imperative to obtain directional information that can be lost on powder samples.
Mineral and mineral type systems were ideal inspirations and testbeds while using this technique, and allowed for magnetically silent building blocks such as oxyanions, to be incorporated into the crystalline lattices to help drive the magnetic ion dimensionality. As previous group members made strides in studying mineralogical building blocks such as silicates, molybdates and vanadates, the logical next development were phosphates and arsenates. In turn this also allowed for the direct comparisons between previously synthesized vanadate samples and what was to come from the exploration of phosphates and arsenates. This became important because many previous examples show that these isostructural building block analogs can have identical atomic structures but very different magnetic structures with no real explanation as to why. The magnetic ions of choice for this work were focused on the first-row transition metal ions. Due to Haldane interactions requiring an odd, whole integer spin value, V3+ and Ni2+ are the only two first row transition metal ions to commonly exhibit such spin values. Additional magnetic ions were also explored even though they are not Haldane candidates, but to develop fundamental knowledge of 1-D magnetic coupling pathways across a range of spin values, considering all magnetic ions have the potential to behave differently according to their environment.
From there, this dissertation sought to expand upon geometric magnetic frustration in exploration of a variety of QSL candidates. Magnetic ion dimensionality focused on variations of 1-D and 2-D systems and hybrid systems that exhibited 2-D layering with distinct 1-D character. Research began with Ni2+ 1-D chains that exhibited increasingly complex magnetic ion arrangements to study if the systems preliminary magnetic data showed any Haldane coupling signatures. One material, Ni2(PO4)(OH), does show initial Haldane characteristics but has a magnetic transition at 31 K which requires additional neutron scattering studies to understand the magnetic complexity of this structure. While this cannot definitively be considered as a Haldane material, it is certainly Haldane-like. With that, not every 1-D Ni2+ system exhibited the highly anticipated Haldane interactions, but fundamental insight was gained in understanding how the atomic structure does affect the potential to access the Haldane coupling mechanism.
In addition to this, the dissertation work expanded into 2-D phase spaces which primarily were dominated by KCoAsO4 which was a highly sought after honeycomb material and proposed to exhibit Kitaev magnetic interactions. While preliminary magnetic results look promising, neutron scattering results are still being processed. Lastly, the work sought to study the Kagome strip class of materials in which are a structural derivative of the traditional Kagome lattice. Preliminary magnetic results indicate spin-flop transitions and high amounts of competing magnetic interactions in which neutron scattering studies have and are still underway to better understand these frustrated interactions. Finally, several other new phases were prepared that display considerable potential as magnetically frustrated materials. The detailed structural aspects of all these compounds are presented along with magnetic studies on many of them. When possible the magnetic measurements were performed on oriented single crystals in the applied fields enabling the determination of anisotropic behavior.
Recommended Citation
Williams, Emily D., "The Exploration of One-Dimensional and Two-Dimensional Frustrated Magnetic Transition Metal Phosphates and Arsenates Via Hydrothermal Synthesis" (2026). All Dissertations. 4327.
https://open.clemson.edu/all_dissertations/4327
Author ORCID Identifier
0000-0003-4658-9677