The design and crystal growth of oxides and fluorides for the study of geometrically frustrated magnetism

Abstract

The symmetry and balance in nature persists down to the atomic scale. The symmetry of properties observed in the macroscopic world is the same as that of the underlying atomic symmetry. Solid-state chemists have the opportunity to explore the rich relationship between the structure and properties of materials. Fundamental research in the area of magnetic frustration provides a target to explore these relationships, which can lead to, discoveries of materials that help advance basic condensed matter physics or everyday technology. To the solid-state chemist, the entire process is a combination of adventure, art, complexity, and hard manual labor. This dissertation provides a window into this process, and focuses on a few groups of materials to show that the structure and properties are intimately intertwined.

Frustrated magnetism is most often found to coexist with layered crystal structures. A family of materials known as Langasites shows a great deal of flexibility in the crystal structure, which makes them ideal for the exploration of structure-property relationships. Work on a series of lead-containing compounds illustrates the complex subtleties of the structure and how small crystallographic distortions produce complex magnetic properties. Similarly, Na2IrO3 also has a layered, magnetically frustrated structure, and is of great interest in condensed matter physics. Work on Na2IrO3 also illustrates how structural details can be very important to the overall chemical stability, and how the decomposition in air can have profound effects on the magnetic properties.

Pyrochlores differ from the other materials presented here in that they possess a three-dimensional structure. Specifically the pyrochlores presented here also are fluorides, which makes their synthesis extremely challenging. Traditionally the pyrochlores most commonly studied are oxides. These fluorides open the door to a new field of compounds not previously explored for magnetic frustration. The work on these pyrochlores demands a high level of skill from solid-state chemists. Encompassing the material design, experimental apparatus construction, synthesis, crystal growth, and characterization, this work shows all facets of work in solid-state chemistry.