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@PHDTHESIS{Bouaziz:771422,
author = {Bouaziz, Juba},
othercontributors = {Lounis, Samir and Honerkamp, Carsten},
title = {{S}pin-orbitronics at the nanoscale : from analytical
models to real materials},
volume = {204},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Forschungszentrum Jülich},
publisher = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
reportid = {RWTH-2019-10151},
isbn = {978-3-95806-429-4},
series = {Schriften des Forschungszentrums Jülich. Reihe
Schlüsseltechnologien/ key technologies},
pages = {1 Online-Ressource (228 Seiten) : Illustrationen,
Diagramme},
year = {2019},
note = {Druckausgabe: 2019. - Onlineausgabe: 2019. - Auch
veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen, 2019},
abstract = {This thesis provides a theoretical description of magnetic
nanostructures in inversion asymmetric environments with
strong spin-orbit interaction (SOI). The theoretical
concepts introduced here can be applied in the field of
spin-orbitronics, which consists of exploiting the SOI to
manipulate the electron spin without external magnetic
fields. The investigated systems display a plethora of
interesting phenomena ranging from chiral magnetic
interactions to gapped magnetic excitations. In practice, we
adopt two different approaches: First, a model-based one
relying on the Rashba Hamiltonian, which is employed to
demystify and understand magnetic and transport properties
of magnetic nanostructure sembedded in a Rashba electron
gas. Second, we use a first-principles approach within the
framework of the Korringa-Kohn-Rostoker (KKR) Green function
method to investigate the ground state properties of
magnetic impurities in topologically insulating hosts. This
method is suitable to simulate nanostructures in real space.
Then, we employed our newly developed code based on
time-dependent density functional theory to compute the spin
excitation spectra of these magnetic nanostructures embedded
in topological insulators. Moreover, the KKR Green function
method was used to simulate the electronic structure and
ground state properties of large magnetic nanostructures,
namely magnetic Skyrmions. In the first part, the analytical
Rashba Green function and the scattering matrices modelling
the magnetic impurities in the s-wave approximation are
employed for the computation of the magnetic interaction
tens or which contains: isotropic exchange,
Dzyaloshinskii-Moriya (DM) and pseudo-dipolar interactions.
The competition between these interactions leads to a rich
phase diagram depending on the distance between the magnetic
impurities. Next, we consider an external perturbing
electric field and investigate the transport properties by
computing the residual resistivity tensor within linear
response theory. The contribution of SOI is explored. The
investigation of arbitrary orientations of the impurity
magnetic moment allowed a detailed analysis of contributions
from the isotropic magnetoresistance and planar Hall effect.
Moreover, we calculate the impurity induced bound currents
in the Rashba electron gas, which are used to compute the
induced orbital magnetization. For a trimer of impurities
with a non-vanishing spin chirality (SC) a finite orbital
magnetization is observed when SOI is turned off. Since it
emerges from the SC, it was named chiral orbital
magnetization. In the second part, we investigate the doping
of topological insulators with magnetic impurities, which
breaks time-reversal symmetry, leading to the prediction of
a gap opening at the Dirac point when the magnetic moments
are oriented in the perpendicular direction with respect to
the surface of the topological insulator. This could
potentially functionalize the topological surface states by
enabling the control of the quantum anomalous Hall effect
and dissipationless transport. Several experimental
investigations obtained conflicting results, generating a
lot of controversy on this point. Since the orientation of
the magnetic moments depends on their magnetic anisotropy
energy, we use the KKRGreen function method to investigate
isolated 3d and 4d transition metal impurities on the
surfaces and in the bulk of Bi2Te3 and Bi2Se3. We explore
the impact of impurity induced in-gap states on the
orientation of the magnetic moments, their dynamical
spin-excitations and on the zero-point spin-fluctuations
affecting the magnetic stability. We propose to use scanning
tunneling spectroscopy in the inelastic mode to verify our
predictions. In the third part, we focus on magnetic
Skyrmions which are topologically protected spin textures.
These magnetic entities can be stabilized by the DM
interaction. Relying on the KKR method we access the
electronic structure of sub-5 nm Skyrmions and propose the
spin mixing tunneling magnetoresistance (TXMR) for an
all-electrical detection of Skyrmions in devices.
Furthermore, we suggest to use X-ray magnetic circular
dichroism(XMCD) as a magnetic microscopy technique for
optical detection of non-collinear spin textures such as
Skyrmions. This can be achieved due to a chiral contribution
to the orbital moments, driven by the non-collinear spin
texture, and acquiring a topological nature for large
Skyrmions.},
cin = {139830 / 130000},
ddc = {530},
cid = {$I:(DE-82)139830_20160118$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2019-10151},
url = {https://publications.rwth-aachen.de/record/771422},
}
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