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PROPERTIES OF MAGNETIC NANOSTRUCTURES
by
Wen Zhang
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PHYSICS)
August 2010
Copyright 2010 Wen Zhang
Object Description
| Title | Properties of magnetic nanostructures |
| Author | Zhang, Wen |
| Author email | wenzhang@usc.edu; vincentzhw@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Physics |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2010-01-21 |
| Date submitted | 2010 |
| Restricted until | Unrestricted |
| Date published | 2010-06-19 |
| Advisor (committee chair) | Haas, Stephan |
| Advisor (committee member) |
Dappen, Werner Bickers, Nelson Nakano, Aiichiro Zhang, Jianfen |
| Abstract | The study of magnetic nanoparticles has been evolving into a rich and rapidly growing research area during the last two decades, featuring many novel phenomena and potential applications. As their characteristic spatial dimensions are sufficiently small, the shape of these nanoparticles becomes one of the dominant factors in determining their magnetic properties. A great variety of magnetic configurations which do not exist in bulk materials have been observed, and many new phenomena have been discovered recently.; In this thesis, we study the static and quasistatic properties of nanomagnets, including their phase diagrams, anisotropy and magnetization reversal processes. A recently developed scaling approach is shown to be effective for nanomagnetic systems, enabling researchers to use small systems to study larger ones. Regarding the numerical method, instead of the widely used Fast Fourier Transform, we have adapted a Cartesian Coordinates based Fast Multipole Method (FMM) for point dipolar magnetic systems and showed its superiority.; In this thesis, we first analyze the magnetic phase diagrams of single-domain nanoparticles with various geometric shapes, crystalline anisotropies and lattice structures. Then we mainly focus on two geometries: square and ring shapes. For square nanomagnets, a systematic study of the configurational anisotropy (CA) is performed varying their edge length, height, exchange coupling constant and external magnetic field. The CA is a special type of anisotropy, existing only in nanomagnets, which results from the deviation of the magnetization configuration from a uniform distribution. We identified four types of anisotropy symmetry, clarifying some existing confusion in literature. Then, the relation between CA and superparamagnetism is discussed. For ring structures, we have focused on their switching hysteresis curves, namely on their magnetization reversal processes. We discovered three new types of switching mechanisms and present here complete in-plane uniform field switching phase diagrams. We review all the possible (meta)stable states in ring structures and discuss in detail all six different types of switching process. Finally, their potential data storage applications are discussed. |
| Keyword | anisotropy; fast multipole method; hysteresis; magnetization reversal; nanomagnet; phase diagram; switching |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3142 |
| Rights | Zhang, Wen |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Zhang-3717 |
| Archival file | uscthesesreloadpub_Volume51/etd-Zhang-3717.pdf |
Description
| Title | Page 1 |
| Full text | PROPERTIES OF MAGNETIC NANOSTRUCTURES by Wen Zhang A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (PHYSICS) August 2010 Copyright 2010 Wen Zhang |
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