Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Physics and Astronomy

First Advisor

Dr. Lance E. De Long

Abstract

Quasicrystals have been shown to exhibit physical properties that are dramatically different from their periodic counterparts. A limited number of magnetic quasicrystals have been fabricated and measured, and they do not exhibit long-range magnetic order, which is in direct conflict with simulations that indicate such a state should be accessible. This dissertation adopts a metamaterials approach in which artificial quasicrystals are fabricated and studied with the specific goal of identifying how aperiodicity affects magnetic long-range order. Electron beam lithography techniques were used to pattern magnetic thin films into two types of aperiodic tilings, the Penrose P2, and Ammann-Beenker tilings. SQUID magnetometer measurements were performed on sample artificial quasicrystals, and their low-temperature, ground-state magnetization textures were directly imaged using X-ray photoemmission electron microscopy (PEEM) and scanning electron microscopy with polarization analysis (SEMPA) techniques. Monte Carlo simulations of the ground state configurations for Penrose P2 and Ammann-Beenker tilings indicate the emergence of complex ordered sublattices that have not been previously observed in periodic systems. Magnetic imaging of artificial quasicrystals show regions of long-range order in an imperfectly equilibrated state. Defects are found between superdomain walls and between smaller, highly correlated vertex clusters. These results bear on the current lack of evidence for long-range magnetic order in three-dimensional atomic quasicrystals.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.409

Funding Information

Research was performed with the support of the U.S. National Science Foundation Grant No. DMR-1506979. 6/1/2015 - 8/1/2019

Research was performed with the support of the U.S. DoE Grant DE-FG02-97ER45653. 5/24/2012 - 6/1/2015

Available for download on Thursday, September 30, 2021

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