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Order and interfaces in epitaxial heterostructures: Structure and magnetism
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.ORCID iD: 0000-0001-9502-8599
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work in this dissertation is devoted to investigating order and interfaces in epitaxial heterostructures. To achieve that the software tool box GenL was developed for simulating and fitting x-ray diffraction patterns from epitaxial thin films, which is used to access structural information on the length scales of interfaces and atomic bonds. Employing GenL, it is shown that a small lattice mismatch between substrate and epitaxial layer is not the sole origin of high crystal quality, as demonstrated for nearly strain-free epitaxial growth of tungsten on sapphire with a lattice mismatch of up to 19.4 %. Furthermore, it is discussed that electronic states at the substrate/film interface can have substantial significance for the crystal structure of an epitaxial layer. For instance, despite a nearly mismatch-free interface of body-centered cubic iron on spinel, the presence of a boundary-induced interface layer with tetragonally distorted crystal structure is discovered, which has a profound impact on the magnetic properties. Finally, when creating multilayered structures, not only the interface states but the total structure is found to influence the physical properties, which is demonstrated for the interlayer exchange coupling in [Fe/MgO]Nsuperlattices.

Note: This PhD thesis is partly based on the licentiate dissertation "Growth of high quality Fe thin films" by Anna L. Ravensburg, Uppsala University, 2022. Particularly parts of: Chapter 1, Sections 2.0, 2.1, 2.2, 3.0, 3.1, 3.2, 3.3, 5.1, and Fig. 2.6 are adapted from the licentiate thesis with minor edits and updates.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. , p. 106
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2356
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-520686ISBN: 978-91-513-2010-6 (print)OAI: oai:DiVA.org:uu-520686DiVA, id: diva2:1827536
Public defence
2024-03-01, Heinz-Otto Kreiss Föreläsningssal, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2024-02-07 Created: 2024-01-15 Last updated: 2024-03-12
List of papers
1. GENL: An extensible fitting program for Laue oscillations
Open this publication in new window or tab >>GENL: An extensible fitting program for Laue oscillations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

GENL is a flexible program that can be used to simulate and/or fit x-ray diffraction data from epitaxial thin films exhibiting Laue oscillations. It utilizes differential evolution within a genetic algorithm for the fitting of data and is based on the kinematic theory of diffraction. Effects of polarization, absorption, the Lorentz factor, as well as instrumental resolution and vibrations are taken into account. Useful parameters that can be extracted after fitting include: atomic interplanar spacings, number of coherently scattering atomic planes, strain profiles along the film thickness, and crystal roughness. The program has been developed in MATLAB and employs a graphical user interface. The deployment strategy is twofold whereby the software can either be obtained in source code form and executed within the MATLAB environment, or as a pre-compiled binary for those who prefer not to run it within MATLAB. Finally, GENL can easily be extended to simulate multilayered film systems, superlattices, and films with atomic steps. The program is released under the GNU General Public Licence. 

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-520681 (URN)10.48550/arXiv.2310.13539 (DOI)
Available from: 2024-01-14 Created: 2024-01-14 Last updated: 2024-01-15
2. Influence of misfit strain on the physical properties of Fe thin films
Open this publication in new window or tab >>Influence of misfit strain on the physical properties of Fe thin films
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2022 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 761, article id 139494Article in journal (Refereed) Published
Abstract [en]

We investigate the growth of thin Fe layers on MgAl2O4 (001) and MgO (001) substrates using dc magnetron sputtering. The crystal quality of Fe layers deposited on MgAl2O4 is found to be substantially higher as compared to Fe grown on MgO substrates. The effects of the crystal quality on the magnetic and electric transport properties are discussed. 

Place, publisher, year, edition, pages
Elsevier, 2022
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-473435 (URN)10.1016/j.tsf.2022.139494 (DOI)000867640600006 ()
Funder
Swedish Research Council, 2019-03581Swedish Research Council, 2019-05379Swedish Energy Agency, 2020-005212
Available from: 2022-04-26 Created: 2022-04-26 Last updated: 2024-04-22Bibliographically approved
3. Boundary-induced phase in epitaxial iron layers
Open this publication in new window or tab >>Boundary-induced phase in epitaxial iron layers
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We report the discovery of a boundary-induced body-centered tetragonal (bct) iron phase in thin films deposited on MgAl2O4 (001) substrates. We present evidence for this phase using detailed x-ray analysis and ab-initio density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetisation direction are observed, as compared to body-centered cubic (bcc) iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultra-thin iron layers. 

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-520682 (URN)
Available from: 2024-01-14 Created: 2024-01-14 Last updated: 2024-01-15
4. Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion
Open this publication in new window or tab >>Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion
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2024 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 130, no 2, article id 74Article in journal (Refereed) Published
Abstract [en]

The conditions whereby epitaxy is achieved are commonly believed to be mostly governed by misfit strain. We report on a systematic investigation of growth and interface structure of single crystalline tungsten thin films on two different metal oxide substrates, Al2O3 (11‾20) and MgO (001). We demonstrate that despite a significant mismatch, enhanced crystal quality is observed for tungsten grown on the sapphire substrates. This is promoted by stronger adhesion and chemical bonding with sapphire compared to magnesium oxide, along with the restructuring of the tungsten layers close to the interface. The latter is supported by ab initio calculations using density functional theory. Finally, we demonstrate the growth of magnetic heterostructures consisting of high-quality tungsten layers in combination with ferromagnetic CoFe layers, which are relevant for spintronic applications.

Place, publisher, year, edition, pages
Springer, 2024
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-520683 (URN)10.1007/s00339-023-07212-w (DOI)001137900100005 ()
Funder
Swedish Research Council, 2019-03581Swedish Research Council, 2021-0465Swedish Energy Agency, 2020-005212Olle Engkvists stiftelse, 217-0023National Academic Infrastructure for Supercomputing in Sweden (NAISS)Swedish Research Council, 2022-06725
Available from: 2024-01-14 Created: 2024-01-14 Last updated: 2024-01-31Bibliographically approved
5. The effect of iron layer thickness on the interlayer exchange coupling in Fe/MgO (001) superlattices
Open this publication in new window or tab >>The effect of iron layer thickness on the interlayer exchange coupling in Fe/MgO (001) superlattices
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We describe the effect of the Fe layer thickness on the antiferromagnetic interlayer exchange coupling in [Fe/MgO]N superlattices. An increase in coupling strength with increasing Fe layer thickness is observed, which highlights the need of including the extension of both the layers when discussing the interlayer exchange coupling in superlattices.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-520684 (URN)
Available from: 2024-01-14 Created: 2024-01-14 Last updated: 2024-01-15

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