Doctoral Dissertations

Date of Award

12-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Haidong Zhou

Committee Members

Hanno Weitering, David Mandrus, Takeshi Egami

Abstract

Geometrical frustration refers to the inability of a complex system to satisfy all its competing interactions within an underlying topological constrained lattice. The two-dimensional kagome lattice is one of the most frustrated lattices and has been a favorite in the theoretical condensed matter community. However, the large variety of exotic states predicted in kagome lattices lies in contrast to a paucity of experimental systems, making new kagome lattice compounds highly desired.

In this dissertation, I shall provide a systematic study of the structural and magnetic properties of a new compounds family, A2RE3Sb3O14 (A = Mg, Zn; RE = Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb). These compounds feature a hitherto unstudied \tripod kagome lattice (TKL)" that was realized by partial ion substitution in the pyrochlore structure. In this dissertation, I shall first brie y introduce the frustrated magnetism and experimental methods in the first two chapters. The third part will cover some general aspects of the TKL, including its structural relation to the pyrochlore lattice, the unique tripod-like spin anisotropies, and spin Hamiltonian. In the fourth chapter, I shall present susceptibility (dc, ac) and specific heat measurements and do a case by case investigation of their magnetic ground states. These include non-collinear spin orders, dipolar spin orders, spin glasses, magnetic charge orders, and several quantum spin liquids. These ground states are compared with the parent pyrochlore lattice and are understood from the standpoint of a balance among spin-spin interactions, anisotropies and Kramers/non-Kramers nature of single ion state. In the fifth chapter, an in-depth neutron scattering study of Mg2Ho3Sb3O14 is provided, demonstrating the system to be a kagome spin ice from a transverse Ising model. The last section contains the conclusions of this dissertation and offers perspectives for future work.

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