Date of Award

2006

Degree Type

Thesis

Degree Name

Doctor of Philosophy

Program

Physics

Supervisor

Dr. Michael Cottam

Abstract

Recent Brillouin light scattering experiments on ferromagnetic nanowire arrays together with advances in materials growth techniques have motivated general interest in the spin-wave dynamics of magnetic nanowires. In the first part of this thesis a microscopic theory is developed for the exchange-dominated spin waves in ferromagnetic films with one or more perpendicular truncations. Extensions are then made to long ferromagnetic nanowires with a general cross sectional shape. As examples, this theory is applied to magnetic strips with grooves, ridges or steps, as well as to some wires composed oftwo different materials in epitaxial contact. In the next several chapters the calculations are generalized to the dipole-exchange spin waves in long antiferromagnetic nanowires with rectangular cross section. The model now includes exchange interactions (along and perpendicular to the wire axis), the long-range dipole-dipole interactions, single-ion anisotropy (which stabilizes the overall antiferromagnetic ordering) and an applied magnetic field. As in bulk materials there are three equilibrium configurations depending of the magnitude of the applied field. These are the low-field antiferromagnetic (AF) phase, the intermediate spin-flop (SF) phase, and the high-field ferromagnetic (F) phase. The spectrum discrete coupled spin waves is calculated for each phase separately. The transition fields between the different phases are also studied with regards to finite-size effects and effects of the dipolar interactions. The dipolar interactions lead to a general reduction of the transition fields compared with the exchange limit. These calculations show a hysteresis type of effect in the AF <> SF phase transition for the nanowires, while there is a smooth transition between the SF and the F phases. Finally a Green’s function method is applied to the antiferromagnetic nanowires in the AF phase. The Green’s functions provide more detailed information about the dynamics of the system. Results are deduced for the relative spectral intensities of the spin-wave excitations and for the average square amplitude and ellipticity ofprecession for the spins in the system

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.