Properties of magnetic thin film devices cannot be understood without detailed knowledge of their structure. For this purpose, a variety of thin film and multilayer systems have been studied. Both reciprocal space (low energy electron diffraction, reflection high energy electron diffraction, X-ray diffraction and reflectometry) and direct space (transmission electron microscopy) as well as Rutherford backscattering spectrometry have been applied. To gain understanding of an oxidation procedure for the growth of magnetite layers, thermal stability of iron layers on molybdenum seed layers has been investigated. Following the mosaicity and the out-of-plane coherence length over different ratios between the constituting layers allowed a deeper understanding of the limits of metallic superlattices. This, together with an approach to use hydrogen in the process gas during magnetron sputter epitaxy, opens routes for the growth of metallic superlattices of superior quality. A non-isostructural multilayer/superlattice system, Fe/MgO, has been investigated. In turn, this gave more understanding how superlattice diffraction patterns are suppressed by strain fields. As an alternative route to single-crystalline superlattices, amorphous multilayers present interesting opportunities. In this context, crystallization effects of iron/zirconium layers on alumiunium oxide were studied. Understanding these effects enables significant improvement in the quality of amorphous multilayers, and allows avoiding these, growing truly amorphous layers. Both the substantial improvement in quality of metallic superlattices, approaching true single-crystallinity, as well as the improvements in the growth of amorphous multilayers give rise to opportunities in the field of magnetic coupling and superconducting spin valves.

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Thin metallic films with magnetic properties like magnetite are an interesting material in current technological applications. In the presented work the iron oxide films are grown by molecular beam epitaxy on MgO(001) substrates at temperatures between room temperature and 600K. The film and surface structure are investigated by x-ray reflectometry (XRR), x-ray diffraction (XRD) and low energy electron diffraction (LEED). The chemical properties are investigated by x-ray photoelectron spectroscopy (XPS). Furthermore, charge transfer multiplet (CTM) calculations are performed as a means to gain additional information from photoemission spectra. It is shown that only for temperatures higher than 500K the oxide film forms a spinel structure. A previously unobserved (2x1) surface reconstruction in two orthogonal domains is found for various preparation conditions. The application of CTMs results in good quantitative and qualitative agreement to other methods for the determination of the film stoichiometry. In addition CTMs can well describe the segregation of Mg atoms into the oxide film either during film growth or during film annealing. It is found that initially Mg substitutes Fe on all possible lattice sites, only for prolonged treatment at high temperature do Mg atoms favour the octahedral lattice sites of divalent Fe.

MnSi(111) films were grown on Si(111) substrates by solid phase epitaxy (SPE) and molecular beam epitaxy (MBE) to determine their magnetic structures. A lattice mismatch of -3.1% causes an in-plane tensile strain in the film, which is partially relaxed by misfit dislocations. A correlation between the thickness dependence of the Curie temperature (TC) and strain is hypothesized to be due to the presence of interstitial defects. The in-plane tensile strain leads to an increase in the unit cell volume that results in an increased TC as large as TC = 45 K compared to TC = 29.5 K for bulk MnSi crystals. The epitaxially induced tensile stress in the MnSi thin films creates an easy-plane uniaxial anisotropy. The magnetoelastic coefficient was obtained from superconducting quantum interference device (SQUID) magnetometry measurements combined with transmission electron microscopy (TEM) and x-ray diffraction (XRD) data. The experimental value agrees with the coefficient determined from density functional calculations, which supports the conclusion that the uniaxial anisotropy originates from the magnetoelastic coupling. Interfacial roughness obscured the magnetic structure of the SPE films, which motivated the search for a better method of film growth. MBE grown films displayed much lower interfacial roughness that enabled a determination of the magnetic structure using SQUID and polarized neutron reflectometry (PNR). Out-of-plane magnetic field measurements on MBE grown MnSi(111) thin films on Si(111) substrates show the formation of a helical conical phase with a wavelength of 2?/Q = 13.9 ± 0.1 nm. The presence of both left-handed and right-handed magnetic chiralities is found to be due to the existence of inversion domains that result from the non-centrosymmetric crystal structure of MnSi. The magnetic frustration created at the domain boundaries explains an observed glassy behaviour in the magnetic response of the films. PNR and SQUID measurements of MnSi thin films performed in an in-plane magnetic field show a complex magnetic behaviour. Experimental results combined with theoretical results obtained from a Dzyaloshinskii model with an added easy-plane uniaxial anisotropy reveals the existence of numerous magnetic modulated states that do not exist in bulk MnSi. It is demonstrated in this thesis that modulated chiral magnetic states can be investigated with epitaxially grown MnSi(111) thin films on insulating Si substrates, which offers opportunities to investigate spin-dependent transport in chiral magnetic heterostructures based on this system.

In the presented thesis thin praseodymia films on non-passivated and passivated Si(111) substrates were investigated. The first part deals with PDA of praseodymia films with fluorite structure under UHV conditions in the temperature region from RT to 600°C. Here, a sophisticated model of the annealing process of praseodymia films is established. This is done by detailed analysis of XRD measurements using the kinematic diffraction theory in combination with the analysis of GIXRD, XRR and SPA-LEED measurements. It is shown that the untreated films, which are oxidized in 1 atm oxygen to obtain fluorite structure, do not exhibit pure PrO2 stoichiometry as it was assumed before. Instead, they decompose into two laterally coexisting species exhibiting a PrO2 and a Pr6O11. oxide phase, respectively. These species are laterally pinned to the lattice parameter of bulk Pr6O11. Homogeneous oxide films with Pr6O11 phase can be observed after annealing at 100°C and 150°C. Here, lateral strain caused by the pinning of the species is minimized and an increase of the crystallite sizes is determined. If higher annealing temperatures are applied, the film decomposes again into two coexisting species. Finally, after annealing at 300°C, a mixed crystalline film with both Pr2O3 and Pr2O3+Delta oxide phases is formed, where Delta denotes a considerable excess of oxygen within the sesquioxide phase. Again the lateral strain increases due to the tendency of praseodymia phases to increase their lattice parameters during oxygen loss combined with the lateral pinning. This is accompanied by a decrease of crystallite sizes, which are afterwards comparable to those of the untreated films. Further annealing at temperatures above 300°C does not significantly change the structure of the oxide film. However, the increase of the amorphous Pr-silicate interface between Si substrate and oxide at the expense of the crystalline oxide can be observed after annealing at higher temperatures. Furthermore, an increased mosaic spread of the crystallites occurs, which reduces the lateral strain caused by the oxygen loss. Nevertheless, the crystalline structure is stable against further annealing up to temperatures of 600°C. Transportation of the sample under ambient conditions after annealing at 200°C and 300°C leads to the formation of an additional crystalline structure at the surface which cannot be allocated to any praseodymia phase and may be explained by the contamination of the topmost crystalline layers with Pr-hydroxides. The results obtained from praseodymia films annealed in 1 atm nitrogen show that these films are good candidates to form homogeneous oxide films with pure cub-Pr2O3 structure by subsequent annealing in UHV. Here, a single oxide species is already observed after annealing at 300°C by SPA-LEED measurements which is in contrast to praseodymia films with fluorite structure where higher annealing temperatures (600°C) are necessary. In this case, negative effects like interface growth or increased defect density (mosaics, grain boundaries) can be minimized. Investigations on oxygen plasma-treated praseodymia films to obtain pure PrO2 stoichiometry are presented in the second part. Oxygen plasma-treated samples are compared with samples oxidized in 1 atm oxygen regarding the structure of the crystalline film. For this purpose, XRR and XRD measurements are performed to get structural information of the oxide film, which can be used to identify the corresponding oxide phases. Here, significantly smaller lattice constants of the crystalline oxide species can be observed after plasma treatment, which points to the incorporation of additional oxygen atoms. This verifies former studies, where a higher oxidation state of the oxide film was found by XPS measurements and it shows that plasma-treated films exhibit a higher oxidation state than films oxidized in 1 atm oxygen due to the availability of reactive atomic oxygen in the plasma. Furthermore, the Pr-silicate interface between crystalline film and Si substrate is not increased during plasma treatment. In the last part of the presented thesis, first results from the epitaxy of praseodymia films on Cl-passivated Si substrates are shown. The aim is to suppress the Pr-silicate formation during the growth process. Thus, praseodymia films are grown on passivated and non-passivated substrates to compare the crystallinity of both samples using XSW and LEED measurements. The structure of the oxide films on Cl-passivated Si is determined afterwards by XRR. It is shown that crystalline films with cub-Pr2O3 structure and several nanometer thickness can be successfully grown on Cl-passivated substrates. Here, the Pr-silicate interface layer are restricted to a single mono-layer. In contrast, the films grown on non-passivated substrates are completely amorphous containing Pr-silicates and Pr-silicides.