This work addresses the growth of ultrathin magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) films and their thorough structural, electronic, and magnetic characterization. In a first step, ultrathin Fe3O4 films are grown on SrTiO3(001) substrates by reactive molecular beam epitaxy (RMBE) and the substrate-induced anomalous strain behavior of the films is investigated by complementary high-resolution transmission electron microscopy (HRTEM) and (grazing incidence) X-ray diffraction [(GI)XRD] measurements. Next, an additional CoO film is deposited on similar Fe3O4/SrTiO3(001) heterostructures to demonstrate an alternative route for the synthesis of cobalt ferrite films through the thermally mediated interdiffusion of both oxide films. The evolution from the initial bilayer stacks to completely reacted cobalt ferrite films is extensively monitored by soft and hard X-ray photoelectron spectroscopy (soft XPS and HAXPES) and (GI)XRD. Complete intermixing and formation of single cobalt ferrite films is confirmed by angular-resolved HAXPES (AR-HAXPES) and X-ray reflectivity (XRR). The study of the cationic distribution resulting from this novel synthesis technique and its effects on the magnetic properties of the cobalt ferrite films is the subject of the subsequent part. Here, X-ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry serve as key investigation techniques, which are further complemented by AR-HAXPES and atomic force microscopy (AFM) measurements. In a final step, highly crystalline cobalt ferrite films with different cationic stoichiometries are grown on MgO substrates using RMBE while their growth behavior is captured in real-time using operando XRD. Further structural characterization of the films is carried out by low-energy electron diffraction and XRR, whereas HAXPES and SQUID provide fundamental information on the electronic, chemical, and magnetic properties of the films.
| Identifer | oai:union.ndltd.org:uni-osnabrueck.de/oai:osnadocs.ub.uni-osnabrueck.de:ds-202206017048 |
| Date | 01 June 2022 |
| Creators | Thien, Jannis |
| Contributors | Prof. Dr. Joachim Wollschläger, Dr. Karsten Küpper |
| Source Sets | Universität Osnabrück |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/pdf, application/zip |
| Rights | Attribution-NonCommercial-NoDerivs 3.0 Germany, http://creativecommons.org/licenses/by-nc-nd/3.0/de/ |
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