Development of a relativistic full-potential firstprinciples multiple scattering Green function method applied to complex magnetic textures of nano structures at surfaces
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Beschreibung
This thesis is concerned with the quantum mechanical investigation of a novel class of
magnetic phenomena in atomic- and nanoscale-sized systems deposited on surfaces
or embedded in bulk materials that result from a competition between the exchange
and the relativistic spin-orbit interactions. The thesis is motivated by the observation
of novel spin-textures of one- and two-dimensional periodicity of nanoscale pitch
length exhibiting a unique winding sense observed in ultra-thin magnetic lms on
nonmagnetic metallic substrates with a large spin-orbit interaction. The goal is to
extend this eld to magnetic clusters and nano-structures of nite size in order to
investigate in how far the size of the cluster and the atoms at the edge of the cluster or
ribbon that are particular susceptible to relativistic eects change the balance between
dierent interactions and thus lead to new magnetic phenomena. As an example,
the challenging problem of Fe nano-islands on Ir(111) is addressed in detail as for an
Fe monolayer on Ir(111) a magnetic nanoskyrmion lattice was observed as magnetic
structure.
To achieve this goal a new rst-principles all-electron electronic structure code based
on density functional theory was developed. The method of choice is the Korringa-
Kohn-Rostoker (KKR) impurity Green function method, resorting on a multiple
scattering approach. This method has been conceptually further advanced to combine
the neglect of any shape approximation to the full potential, with the treatment of
non-collinear magnetism, of the spin-orbit interaction, as well as of the structural
relaxation together with the perfect embedding of a nite size magnetic cluster of
atoms into a surface or a bulk environment. For this purpose the formalism makes
use of an expansion of the Green function involving explicitly left- and right-hand
side scattering solutions. Relativistic eects are treated via the scalar-relativistic
approximation and a spin-orbit coupling term treated self-consistently. This required
the development of a new algorithm to solve the relativistic quantum mechanical
scattering problem for a single atom with a non-spherical potential formulated in
terms of the Lippmann-Schwinger integral equation.
Prior to the investigation of the Fe nano-islands, the magnetic structure of an Fe
monolayer is studied using atomistic spin-dynamics on the basis of a classical model
Hamiltonian, which uses realistic coupling parameters obtained from rst principles. It
is shown that this method is capable to nd the experimentally determined magnetic
structure.
Autor*in
David Siegfried Georg Bauer