Synthesis and Characterization of 3D-Ordered and Quasi-1D Magnetic Materials

Abstract

Magnetic materials play a vital role in everyday life and in emerging technology – from the magnetic stripes on credit cards to the development of new materials with possible applications in quantum computation. This dissertation presents the synthesis, structural determination, and physical properties characterization of three new materials with coupled magnetic moments. Synthesis methods include traditional solid-state syntheses under oxidizing and inert atmospheres for new borate and oxide materials, as well as arc-melting synthesis of an intermetallic boride. Structural characterization techniques include single-crystal X-ray diffraction and powder X-ray diffraction, while the physical, thermal, and optical properties are investigated with magnetometry, resistivity, heat capacity, differential scanning calorimetry, and diffuse reflectance absorption spectroscopy.In order to set up a strong basis for understanding the subsequent chapters in this dissertation, chapter 1 discusses the basics of structure and bonding in extended solids, magnetism arising from unpaired electrons in materials, and the synthesis and characterization techniques utilized in the course of this PhD work. In chapter 2, I present a new antiferromagnetically ordered material LaNiB3O7, which is only the third compound discovered in the CaAlB3O7 structure type. With its Néel temperature of 19 K, LaNiB3O7 is the first in this structure type to demonstrate magnetic ordering. Chapter 3 describes the discovery of a metastable polymorph of NdCo2B2, which demonstrates complex magnetic behavior due to its low-symmetry structure, the presence of magnetic Nd and Co, and possible coexistent localized and conduction-electron-mediated magnetic coupling. In chapter 4, I investigate the quasi-one-dimensional magnetism arising in a new oxide semiconductor in the Pb-Re-O ternary system, with heat capacity data revealing possible spinon excitations below 10 K. This dissertation spans a range of material compositions, magnetic properties, and conductive behavior, painting a picture of how the structure, bonding, and electron interactions in materials give rise to their diverse magnetic properties.