D'Aquino, Massimiliano
(2005)
Nonlinear Magnetization Dynamics in ThinFilms and Nanoparticles.
[Tesi di dottorato]
(Inedito)
Tipologia del documento: 
Tesi di dottorato

Lingua: 
English 
Titolo: 
Nonlinear Magnetization Dynamics in ThinFilms and Nanoparticles 
Autori: 
Autore  Email 

D'Aquino, Massimiliano  [non definito] 

Data: 
2005 
Tipo di data: 
Pubblicazione 
Numero di pagine: 
165 
Istituzione: 
Università degli Studi di Napoli Federico II 
Dipartimento: 
Ingegneria elettrica 
Dottorato: 
Ingegneria elettrica 
Ciclo di dottorato: 
17 
Coordinatore del Corso di dottorato: 
nome  email 

Miano, Giovanni  [non definito] 

Tutor: 
nome  email 

Serpico, Claudio  [non definito] 

Data: 
2005 
Numero di pagine: 
165 
Parole chiave: 
micromagnetics, LandauLifshitzGilbert equation, precessional switching, spinpolarized currents, perturbative tecniques, micromagnetic simulations, fast switching, geometrical integration, micromagnetic standard problem n. 4 
Settori scientificodisciplinari del MIUR: 
Area 09  Ingegneria industriale e dell'informazione > INGINF/02  Campi elettromagnetici 
Depositato il: 
02 Mar 2007 
Ultima modifica: 
03 Dic 2014 15:52 
URI: 
http://www.fedoa.unina.it/id/eprint/148 
DOI: 
10.6092/UNINA/FEDOA/148 
Abstract
In chapter 1 the micromagnetic model and the
LandauLifshitzGilbert (LLG) equation is introduced to
describe magnetization phenomena in ferromagnetic bodies.
First, an approach in terms of the
free energy associated with the magnetic body is presented to
derive the static equilibrium conditions for magnetization vector
field. Then, the dynamic effects due to the gyromagnetic
precession are introduced. Both LandauLifshitz and
LandauLifshitzGilbert equation are presented.
Phenomenological Gilbert damping is analyzed in terms of
Rayleigh dissipation function.
In chapter 2 the study of magnetization dynamics in uniformly
magnetized particles is addressed. In particular, first the
static StonerWohlfarth model and then magnetization switching
processes are analyzed. In addition, novel analytical
techniques to study magnetization dynamics under circularly
polarized external fields and magnetization dynamics driven by
spinpolarized currents are introduced and deeply discussed.
In this respect, it is shown how some behaviors indeed
observed in experiments, can be explained in terms of bifurcations
of fixed points and limit cycles of the LLG dynamical system.
As a further step, in chapter 3, the assumption of magnetization
spatial uniformity is removed and the problem of studying
thinfilms reversal processes of technological interest is
addressed. In this respect, as preliminary step, the issue of the
computation of magnetostatic fields, which is still the bottleneck
of micromagnetic simulations, is illustrated together with
the mostly used methods at this time. Then, a comparison of
damping and precessional switching processes in thinfilms is
performed, showing that fast precessional switching can be
considered spatially quasiuniform and, therefore, its crucial
aspects can be analyzed by means of uniform mode theory discussed
in chapter 2. Finally, a uniform mode analysis is applied to
the fast switching of granular tilted media which represents one
of the most promising solutions for high density magnetic storage
in future hard disks.
In chapter 4, the problem of the geometrical integration
of LLG equation is considered. In particular, the midpoint rule
timestepping is applied to the LLG equation. In fact, it
is shown that the fundamental properties of magnetization
dynamics, embedded in the continuous model, are reproduced by the
midpoint discretized LLG equation regardless of the time step. In
addition, since the resulting numerical scheme is implicit,
special and reasonably fast quasiNewton technique is
developed to solve the nonlinear system of equations arising at
each time step. The proposed midpoint technique is validated
on the micromagnetic standard problem no. 4 which concerns with
thinfilms reversal processes. Finally, numerical
results and computational cost are discussed.
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