The Synthesis and Characterization of Novel 2D Rare Earth Oxides for the Study of Frustrated Magnetism

Abstract

Geometric frustration is a rich area of study in condensed matter physics. Competing interactions can result in highly degenerate low temperature states and unusual quantum phenomena, yielding models for probing exotic quasi-particle excitations and statistical mechanics. This dissertation details the synthesis and characterization of novel materials that exhibit geometric frustration. Chapter 1 provides an introduction to solid state chemistry, including the methods and tools of materials characterization. In Chapter 2, the fundamentals of magnetic frustration are explored.

Discovering new rare earth-derived geometrically frustrated materials has been of great interest to enhance the fundamental understanding of lanthanide exchange interactions in frustrated magnetism. In particular, the triangular kagome lattice, which resembles the Chinese checkerboard or the Star of David, is notorious for its frustrated geometry. Chapters 3 through 7 focus on novel materials that assume this kagome structure. In Chapters 3 and 4, the synthesis and properties of compounds with an ideal 2D rare earth kagome lattice, RE3Sb3Zn2O14 (RE= La, Pr, Nd, Sm, Eu, Gd) and RE3Sb3Mg2O14 (RE=La, Pr, Sm, Eu, Sm, Tb, Ho), are investigated. Both sets of materials evade magnetic ordering down to 1.8 K.

Chapter 5 juxtaposes the magnetism and crystal structures of the 2D kagome Nd3Sb3Mg2O14 with that of a corresponding 3D pyrochlore, Nd2ScNbO7. These materials reveal magnetic ordering transitions below 0.6 K.

Chapters 6 and 7 demonstrate the ease of manipulation of the kagome structure with chemical substitution. In Chapter 6, dilution experiments are performed on Nd3-xLaxSb3Mg2O14 and the structures and magnetic properties are assessed. Chapter 7 details the synthesis and physical properties of kagome materials containing both a magnetic rare earth and transition metal, RE3Sb3MnCaO14 and RE3Sb3CoCaO14 (RE=La, Pr, Nd, Sm, Eu).

Chapter 8 focuses on the magnetism of KBaRE(BO3)2 (RE=Sm, Eu, Gd, Tb, Dy, Ho). These materials feature a 2D triangular net of rare earth ions and do not undergo magnetic ordering above 1.8 K. All of the compounds examined in this dissertation open up the door for new and exotic physics. Comprising the design, synthesis, and characterization of extended lattices, this dissertation reveals the many elements involved in solid state chemistry.