Year of Publication

2014

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Physics and Astronomy

First Advisor

Dr. Lance De Long

Abstract

This thesis reports our study of the effect of domain wall pinning by ferromagnetic (FM) metamaterials [1] in the form of periodic antidot lattices (ADL) on spin wave spectra in the reversible regime. This study was then extended to artificial quasicrystals in the form of Penrose P2 tilings (P2T). Our DC magnetization study of these metamaterials showed reproducible and temperature dependent knee anomalies in the hysteretic regime that are due to the isolated switching of the FM segments. Our dumbbell model analysis [2] of simulated magnetization maps indicates that FM switching in P2T is nonstochastic. We have also acquired the first direct, two-dimensional images of the magnetization of Permalloy films patterned into P2T using scanning electron microscopy with polarization analysis (SEMPA). Our SEMPA images demonstrate P2T behave as geometrically frustrated networks of narrow ferromagnetic film segments having near-uniform, bipolar (Ising-like) magnetization, similar to artificial spin ices (ASI). We find the unique aperiodic translational symmetry and diverse vertex coordination of multiply-connected P2T induce a more complex spin-ice behavior driven by exchange interactions in vertex domain walls, which differs markedly from the behavior of disconnected ASI governed only by dipolar interactions.

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