Unit:
Department of PhysicsLibrary of the School of Science
Dissertation committee:
1. Φοίβος Μαυρόπουλος, Καθηγητής Τμήματος Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
2. Yuriy Mokrousov, Professor, Johannes Gutenberg-Universität Mainz and Forschungszentrum Jülich, Γερμανία.
3. Νικόλαος Στεφάνου, Καθηγητής Τμήματος Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών.
4. Marjana Lezaic, Researcher, Forschungszentrum Jülich, Γερμανία.
5. Ιωσήφ Γαλανάκης, Καθηγητής, Τμήμα Επιστήμης Υλικών, Πανεπιστήμιο Πατρών.
6. Αθανάσιος Δημουλάς, Διευθυντής Ερευνών, ΕΚΕΦΕ Δημόκριτος.
7. Γεώργιος Κιοσέογλου, Καθηγητής Τμήματος Επιστήμης Υλικών, Πανεπιστήμιο Κρήτης
Original Title:
Quantum states in materials with complex topological electronic and magnetic structure
Translated title:
Quantum states in materials with complex topological electronic and magnetic structure
Summary:
The research on the complex topological electronic and magnetic structure of materials
has been gaining importance over the last few years, as it can be applied in the field
of spintronics with prospects for implementation in information technology.
The main goal of this thesis is the theoretical and computational study of spin-transport
phenomena in topological structures. Our simulations are based on ab-initio calculations
augmented by electronic scattering theory.
Firstly, we focus on the phenomenon of the spin-orbit torque in a special materials class,
the topological insulators, doped with magnetic impurities. We investigate the spin-orbit
torque exerted on the magnetic moments of ferromagnetically coupled transition-metal
defects (Cr, Mn, Fe, and Co) embedded in the surface of the topological insulator Bi2Te3,
in response to an electrical current flow in the surface. The scattering properties of surface states off multiple magnetic impurities are calculated within the Korringa-Kohn-Rostoker (KKR) Green function method, while the spin-orbit torque calculations are performed by combining the KKR results on the Fermi surface and scattering rate with the semiclassical linearized Boltzmann equation. We discuss the correlation of the spin-orbit torque to the spin current on the Fermi surface, analyzing the spin flux contribution to the spin-orbit torque on the defects. In addition, we relate the torque to the resistivity and the Joule heat production. We find these systems may be favorable for spintronic applications. In particular, we predict that the Mn/Bi2Te3 is the most promising among the studied systems for applications of the spin-orbit torque effect.
Secondly, we focus on magnetic skyrmions in magnetic films, which are two-dimensional
topological solitons that behave like particles that can be formed, transported, detected.
Based on the KKR method, non-collinear spin-density-functional theory calculations are
carried out for the formation of stable magnetic skyrmions in Pd/Fe/Ir(111) ultrathin
films. Next, solving selfconsistently the Boltzmann transport equation, we study the
topological Hall effect (THE) induced by the electron scattering on skyrmion systems.
The investigation of the THE is of pivotal importance in these systems, since it is
one of the key methods for electrically detecting magnetic skyrmions. We present the
resistivity and the Hall angle of the system, and we examine the dependence of the THE
on disorder, modelled by an additional electron scattering term. Our findings predict a
strong dependence of the topological Hall angle on the degree of disorder of the sample.
Main subject category:
Science
Keywords:
spintronics, magnetism, topology, ab-initio simulations, density functional theory, KKR Green function method, electronic structure, Boltzmann formalism, spin-orbit torque, topological insulators, magnetic impurities, magnetic skyrmions, topological Hall effect
Number of references:
143
