Unit:
Department of PhysicsLibrary of the School of Science
Author:
Patsopoulos Aristotelis
Dissertation committee:
Στεφάνου Νικόλαος, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Μαυρόπουλος Φοίβος, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Σταμόπουλος Δημοσθένης, Αναπληρωτής Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Σιμσερίδης Κωσταντίνος, Επίκουρος Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Φραντζεσκάκης Δημήτριος, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Λυκοδήμος Βλάσιος, Επίκουρος Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Κεχράκος Δημήτριος, Αναπληρωτής Καθηγητής, Παιδαγωγικό Τμήμα, ΑΣΠΑΙΤΕ
Original Title:
Δυναμική της μαγνήτισης σε πεπερασμένη θερμοκρασία σύνθετων νανοδομικών υλικών
Translated title:
Magnetization dynamics in finite temperature of complex nanostructured materials
Summary:
Elongatedmagneticnanowiresarecharacterizedbyenhancedanisotropydue
to their shape and hold promises for major advances in different areas of modern
technology ranging from magnetic recording and spintronics to biomedicine. A
new perspective in magnetic memory devices has also emerged, stimulated by
the manifested feasibility to manipulate the domain wall motion in these quasi
one-dimensionalnanostructuresandpavednewpathsforinformationstorageand
spintronics applications. In this effort to develop magnetic materials with desired
properties, the exchange bias effect has long been recognized as a means to
tailor the hysteresis characteristics of nanostructured magnetic materials while
the fundamental research related to magnetic nanostructures remains to reveal
the various factors that govern the magnetization reversal mechanism.
Inchapter1,wedescribethebasicinteractionscontrollingthemagneticbehavior
ofthestudiedsystemsandthemagneticorderingoriginatingfromtheircompetition.
We also perform an introductory interpretation of the exchange - bias effect and
elucidatebasictheoryofmagneticnanowiresandmagneticsolitonictextureswhich
are the fundamentals of this thesis.
In chapter 2, we introduce the computational micromagnetic approach that we
use to model the magnetic structure of the studied systems and the Metropolis
Monte Carlo simulation from which numerical results are derived.
Inchapter3,westudythemagneticpropertiesofcylindricalferromagneticcore
/ antiferromagnetic shell nanowires in order to elucidate the impact of the oxidized
shell on the magnetic properties and the magnetization reversal mechanism. We
find that the coupling to the antiferromagnetic shell introduces a complex reversal
mechanismcomparingwiththebareferromagneticnanowires.Wealsodemonstrate
that the coupling to a polycrystalline antiferromagnetic shell leads to maximum
exchange - bias in an off - axis direction. In addtion, polysrystallinity increases the
critical core diameter for transition from transverse to vortex domain walls. Our
results are in qualitative agreement with recent experimental studies of Co/CoO
nanowires.
“Domain wall traps” have been engineered and well exploited in nanostrips by
creating a geometrical trapping site, e.g. a single notch along a stripe. In chapter
4, we report our systematic study on the domain wall structure and its nucleation
/ propagation in tri-segmented diameter - modulated ferromagnetic nanowires.
We find out that the magnetization behavior of single DM - NWs exhibits the
significance of positional ordering of thick and thin segments, distinguished by
two distinct geometries including: dumbbell - type (type I) and rolling pin - type
(type II). Based on our numerical simulations, it was evidenced that the widenarrow
junctions create trap sites for domain walls where the narrow segment
restricts their motion.
Inchapter5,westudytheformationofmagneticskyrmionsincurvedgeometries
such as nanotubes. We address systematically the impact of curvature in the
formation and in the geometrical features of magnetic skyrmions, defining the
limitations in which this formation is stable.
Finally, in chapter 6, we summarize the basic conclusions of this thesis and we
highlight some open questions for future research.
Main subject category:
Science
Keywords:
Magnetic Nanowires, Exchange Bias, Micromagnetism, Magnetic Solitons
Number of references:
159
