Analysis of Electronic and Magnetic Properties at the Interfaces of Transition Metal Heterostructures
Date
2024-01-12
Authors
Journal Title
Journal ISSN
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Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
Material science is a field of physics that bridges the gap between the microscopic properties
of materials and how these properties manifest as tangible, observable characteristics
that can be observed or harnessed for applications. Material scientists grow, analyze, modify,
and model complex, exotic materials to understand emergent, novel phenomena and create
devices which can readily be employed for electronic, magnetic, and other applications. However,
many material properties cannot be measured or observed directly; it is not feasible
to measure the orbital energies of an atom directly or quantify angstrom-scale magnetic
variations in a thin film sample directly. Since these properties are frequently what create
meaningful effects at a macroscopic level, an understanding of them is required that only
material science techniques can provide. This thesis concerns two separate studies of complicated
material systems that require an understanding of their underlying structure and
properties that cannot be directly discerned by experiment alone. These samples belong to a
class of materials known as heterostructures, structures formed by layering multiple materials
with different chemical/elemental compositions. The junctions where different materials in a
heterostructure connect are called interfaces, and serve as the sites of emergent physical and
chemical phenomena with a myriad of electronic and magnetic applications.
The first material system studied is the interface of bulk LaAlO3 and bulk CaTiO3,
often simply abbreviated as LAO/CTO. Systems containing interfaces between transition
metal compounds have been intensely studied within the past two decades because certain
phenomena such as two-dimensional electron gases (2DEG), magnetism, and other effects
tend to appear specifically around the interface. Historically, a combination of bulk LaAlO3 and bulk SrTiO3 (LAO/STO) was studied instead, but the interfacial effects can be changed
by swapping out various elements in the compound. This variation is due to the crystal
structure near the interface being distorted according to the element introduced, altering the
Ti orbital energies near the interface as well. These near-interface orbital energies directly
correlate to observed interfacial phenomena, so swapping elements is expected to affect the
macroscopic electronic and magnetic properties of the system. The difficulty resides in the
fact that orbital energies and 2DEG charge densities cannot be measured directly by any
experiment; rather, they need to be extracted from experimental data via sophisticated
modelling. The purpose of this study was to probe two samples of LAO/CTO with varying
thicknesses, use the extracted experimental data to generate models of the two samples, and
finally use this model to discern orbital energies. Special consideration was given to comparing
and contrasting the difference between the LAO/STO interfacial electronic structure with
that obtained for LAO/CTO. It was found that the orbital energies of LAO/CTO maintain
a significantly different configuration from those of LAO/STO, and suggest that LAO/CTO
may be more promising for magnetic applications. Furthermore, this difference will foster
more investigation into interfaces of this kind, particularly in designing new configurations
of different metals to observe what macroscopic effects they produce.
The second material system studied is thin films of Fe3GeTe2, often abbreviated FGT.
FGT as a bulk material has been studied since the turn of the millennium for potential
magnetic applications, and attention has recently moved towards growing the substance
in thin film form on the order of angstroms thick. Several sources have found that the
electronic and magnetic properties of these thin films vary dramatically vary dynamically as
more FGT film layers are grown sequentially in one sample. However, this information is only known at a high level; the magnetic effects are known to differ, but how exactly this
manifests on a microscopic level is unknown. Given the angstrom level thickness of the films,
it is extremely difficult to probe the magnetic properties in detail. A more sophisticated
technique is needed, so here we apply resonant X-ray reflectometry. This study considered
two samples: a single FGT layer film (monolayer) and a combination of two FGT layers as
a film (bilayer). Experimental results were used to synthesize a model of each film and the
magnetized iron distribution was quantified in each case. The two samples were found to
have differing magnetized iron distributions, further lending credence to observations that
FGT films of various layers will produce different magnetic properties and effects.
These two studies represent intriguing but very limited applications of material science.
New exotic materials are being actively discovered all the time, each with their own unique
need for a method that probes their microscopic properties to understand macroscopic phenomena.
Material science techniques are and will continue to be important for these reasons;
advancement of technology is now reliant on synthesizing and understanding new materials
that improve electronic and magnetic infrastructures, an understanding that material science
provides.
Description
Keywords
Material science, heterostructures, thin films, synchrotron, resonant x-ray reflectometry, RXR, LAO/CTO, FGT
Citation
Degree
Master of Science (M.Sc.)
Department
Physics and Engineering Physics
Program
Physics