Search

Base metal promoted gold/titania catalysts were synthesized, characterized and tested in CO oxidation reaction. Catalysts containing dopant metals in higher oxidation states exhibited higher activity than catalysts containing dopants in reduced states. The activity of fresh catalysts promoted by Cu, Fe and Ni was similar to the unpromoted one, but treatment in reducing and oxidizing atmospheres revealed the supremacy of the copper promoted catalyst. The sequential deposition method proved to be better than the co-deposition—precipitation method. An attempt to explain these differences using XPS, FTIR and H2 TPR was performed.

We investigated type II bacterial photosynthetic reaction centers, which contain a quinone - iron complex (Q_A-Fe-Q_B) on their acceptor side. Under physiological conditions it was observed mainly in a reduced high spin state but its low spin ferrous states were also observed. Therefore, it was suggested that it might regulate the dynamical properties of the iron–quinone complex and the protonation and deprotonation events in its neighbourhood. In order to get insight into the molecular mechanism of the NHFe low spin state formation, we preformed Mössbauer studies of a wild type of Rb. sphaeroides and its two mutated forms. Our Mössbauer measurements show that the hydrophobicity of the Q_A binding site can be crucial for stabilization of the high spin ferrous state of NHFe.

Different forms of iron compounds embedded in non-functionalized (as prepared) and functionalized multiwall carbon nanotubes (MWCNTs) were studied. Iron used to catalyze MWCNT synthesis can be found inside nanotubes and built-in within their walls. Mossbauer spectroscopy was applied to study valence and spin states as well as magnetic ordering of the iron compounds. In the Mossbauer spectra of as prepared MWCNTs the Fe3C carbide provides the main contribution. The content of Fe3C decreases by about 20 and 40% in carboxylated carbon nanotubes (MWCNTs-COOH) and ammonium salt of carboxylated carbon nanotubes (MWCNTs-COONH4), respectively. A small amount of α-Fe and FexCx iron forms are always observed in all studied carbon nanotubes. In MWCNTs-COOH, additionally, ferrihydrates and/or FexCy with oxygen in the second coordination sphere of iron are present (at a level of about 17%). In MWCNTs-COONH4 their content increases by a factor of 3. The experimental data shows that the purification and functionalization of as prepared MWCNTs result in removal of about 90% of iron contaminations. Additionally, we observe the modification of iron compounds inside MWCNTs. All these results are important in optimizing the as prepared MWCNT purification process and in finding a new way to produce different Fe phases inside MWCNTs.

The potential applications of carbon nanotubes (CNTs) are strongly related to their physical and chemical properties. In this work, results of different methods for the oxidation of crude CNTs are reported. These methods changed Fe binding sites within multiwall carbon nanotubes (MWCNTs). Mossbauer spectroscopy was used to detect the chemical properties of the Fe-phases in MWCNTs. Signals from the iron carbide Fe3C were the main components in the Mossbauer spectra of unmodified MWCNTs revealing magnetic ordering even at 300 K. In oxidized MWCNTs, the amount of Fe3C decreased and γ-Fe and α-Fe, ferrihydrates of iron oxides and different forms of goethite appeared. In MWCNTs oxidized with HClO4, a significant fraction (∼24%) of magnetically ordered Fe2O3 particles was detected. This study showed that traces of iron catalyst embedded in MWCNTs could be used as a sensitive probe to monitor various MWCNT modifications.

Cluster–support interaction in a Au–Fe3O4(0 0 1) system was studied using scanning tunneling microscopy, X-ray photoemission spectroscopy and Mossbauer spectroscopy, in situ, under ultra high vacuum conditions. Deposition of 0.02–5 monolayers of Au resulted in the growth of two- and three-dimensional gold nano-cluster. The positive shift of the Au 4f7/2 electron binding energy for the smallest clusters was correlated with modification of the electronic structure in the surface magnetite layer, as found from Mossbauer analysis, leading to conclusion that a positive charging of small Au clusters can be responsible for their outstanding catalytic activity.

The electronic and magnetic properties of epitaxial Fe 3 O 4 (001) films on MgO(100) substrates were studied throughout the 2.5- to 30-nm thickness range using conversion electron Mossbauer spectroscopy. Despite the superparamagnetism that was observed for film thickness below 5 nm, the Verwey transition persisted even for the thinnest film. Temperature-dependent Mossbauer measurements between 80 K and 400 K revealed that the activation energy for the magnetic moment fluctuations in the 3-nm magnetite film is higher than the magnetic anisotropy energy by an order of magnitude.

We demonstrate that FeRh layers can be implemented to the epitaxial Fe/Au/FeRh spin valve structures grown on MgO(001). Owing to the AFM-FM phase transition in the FeRh film, the magnetic structure of our Fe/Au/FeRh system can be temperature controlled. The indirect exchange coupling between Fe and FeRh films mediated by the Au spacer enables to control the relative orientation of the Fe and FeRh magnetizations by the Au spacer thickness between ferromagnetic and non-collinear with nearly orthogonal magnetizations. Moreover, the evolution of magnetic structure of the Fe/Au/FeRh system along with the AFM-FM transition is accompanied by the reversible in-plane rotation of the top Fe-layer magnetization.We demonstrate that FeRh layers can be implemented to the epitaxial Fe/Au/FeRh spin valve structures grown on MgO(001). Owing to the AFM-FM phase transition in the FeRh film, the magnetic structure of our Fe/Au/FeRh system can be temperature controlled. The indirect exchange coupling between Fe and FeRh films mediated by the Au spacer enables to control the relative orientation of the Fe and FeRh magnetizations by the Au spacer thickness between ferromagnetic and non-collinear with nearly orthogonal magnetizations. Moreover, the evolution of magnetic structure of the Fe/Au/FeRh system along with the AFM-FM transition is accompanied by the reversible in-plane rotation of the top Fe-layer magnetization.

Series of Fe3O4/MgO(001) and Fe3O4/Fe/MgO(001) films (single- and bi-layer films, respectively) with a total layer thickness in the range of 20¥150 nm were investigated by the Rutherford backscattering spectrometry (2 MeV He+ ion beam), by the Rutherford backscattering spectrometry channeling experiments (1.5 MeV He+ ion beam). Depending on the layer thickness of each layer and the film geometry, a single Fe peak and/or a double-anomaly feature was revealed in the Rutherford backscattering spectra. For all films no magnesium presence in the surface layer was observed. For both single- and bi-layer films with a total layer thickness less than 60 nm only one minimum was observed in the channeling curves, while a double minimum was revealed for the bi-layer films with a larger thickness. X-ray reflectometry measurements have revealed that the film density is the same as that of the bulk one.

A study of in-plane magnetic anisotropy (MA) in epitaxial bcc Co films and Fe/Co bilayers on a Fe(110) surface is reported. Surface MA of as-deposited Co films and Fe/Co bilayers strongly depends on the Co (dCo) and Fe (dFe) thickness. Adsorption of residual gases drastically modifies in-plane MA of both Co films and Fe/Co bilayers. We present two dimensional MA maps in the (dCo, dFe) space for both as grown and adsorption-modified films. Our results indicate how to precisely engineer in-plane MA that can be controlled by dCo, dFe and is sensitive to the residual gas adsorption.

The XPS technique was applied to study Au deposition on defect-rich MgO(100) surfaces in a coverage range of 0.2-5 Au manolayers. Three MgO surfaces were used with increasing concentration of surface defects as determined based on surface composition and modified Auger parameter: air-cleaved, ultrahigh-vacuum-cleaved, and polished. The analysis of the Au 4f core excitation intensities showed 3D-island growth of Au. The Au 4f binding energy was shown to decrease with increasing Au coverage, with a dependence on the substrate type.

We used nuclear hyperfine spectroscopies and a 57 Fe probe layer approach to study the depth-dependent magnetic properties of ultrathin Fe films on NiO(0 0 1), a system exhibiting exchange bias. Conversion electron Mossbauer spectroscopy and nuclear resonance scattering of synchrotron radiation were employed. The samples were two Fe films with a thickness (8–10 ML) slightly above the critical thickness for the onset of ferromagnetism at room temperature, in which a 2 ML-thick probe layer, enriched in the 57 Fe Mossbauer isotope, was embedded at different depths from the Fe/NiO interface. Both techniques indicate that inside the film Fe has a metallic character, while at the interface with NiO different Fe phases are present. The main conclusion is that already a few monolayers from the interface with NiO the magnetic properties of Fe are bulk-like.

Epitaxial Fe3O4(0 0 1) thin films (with a thickness in the range of 10–20 nm) grown on MgO substrates were characterized using low-energy electron diffraction (LEED), conversion electron Mossbauer spectroscopy (CEMS) and investigated using Rutherford backscattering spectrometry (RBS), channeling (RBS-C) experiments and X-ray reflectometry (XRR). The Mg out-diffusion from the MgO substrate into the film was observed for the directly-deposited Fe3O4/MgO(0 0 1) films. For the Fe3O4/Fe/MgO(0 0 1) films, the Mg diffusion was prevented by the Fe layer and the surface layer is always a pure Fe3O4 layer. Annealing and ion beam mixing induced a very large interface zone having a spinel and/or wustite formula in the Fe3O4-on-Fe film system.

The interface reactions in an epitaxial 10 nm-thick Fe3O4/MgO(0 0 1) film were investigated by using Rutherford Backscattering spectrometry (RBS), channeling (RBS-C) and X-ray reflectometry (XRR). The as-grown film had a good crystallinity indicated by the minimum yield and the half-angle value for Fe, respectively, χmin(Fe) = 22% and ψ1/2(Fe) = 0.62°. Annealing the films under partial argon pressure up to 600 °C led to a large enhancement of Mg out-diffusion into the film forming a wustite-type phase, but the total layer thickness did not change much. Ion irradiation of the film by 1 MeV Ar ion beam caused a strong Fe ion mixing resulting in a large interfacial zone with a thickness of 23 nm.

Epitaxially-grown Fe3O4(0 0 1) thin films by reactive deposition on MgO(1 0 0) substrates were studied using low-energy electron diffraction (LEED), conversion electron Mossbauer spectroscopy (CEMS), Rutherford backscattering spectrometry (RBS), channeling (RBS-C) experiments and X-ray reflectometry (XRR). No visible influence from the ion irradiation of the samples on the CEMS spectra was found, while surface oxidation of the samples was observed after exposure to the atmospheric pressure. RBS analysis indicated the presence of magnesium with an average amount of 3% in the films. RBS-C experiments yielded a value of 22% for the minimum yield of Fe and a value of 0.62° for the half-angle for Fe in the film indicating a good crystal quality of the films. The value for film-thickness obtained from XRR is in a good agreement with that from RBS and the nominal value.

We report on nuclear resonant scattering (NRS) studies of the electric field gradient (EFG) of a clean Fe monolayer on W(1 1 0) and its changes upon adsorption of residual gases. The consecutive NRS time spectra indicate a gradual tilt of the EFG main axis from perpendicular orientation for the as-prepared monolayer to the in plane one as a result of increasing adatom concentration.

The initial growth and influence of annealing on structural and magnetic properties of 5 monolayers epitaxial Fe films on cleaved and polished MgO(0 0 1) substrates was studied using conversion electron Mossbauer spectroscopy (CEMS). Broadening of LEED spots indi- cated a granular structure of the films grown at room temperature. The CEMS analysis showed that the film on the cleaved substrate is flat and consists of a 2 ML interfacial layer with the electronic structure affected by the oxidic substrate, while the remaining 3 ML are metallic with the Curie temperature below RT. Annealing changes the film structure, as seen by CEMS, but only for temperatures above 550 K. In the annealing process the continuous film breaks into 3-dimensional islands and oxidation takes place at the Fe/cleaved-MgO interface. On the polished substrate, the as-prepared film consists of small superparamagnetic metallic iron particles. Contrary to the cleaved substrate, no oxidation is observed at the interface upon annealing. � 2007 Elsevier B.V. All rights reserved.

We investigated changes in the magnetic properties of a single Fe monolayer on Au(0 0 1) induced by the interlayer exchange coupling (IEC) to FeAu monoatomic superlattices. The grazing incidence nuclear resonant scattering of X-rays (GI-NRS) combined with the 57 Fe probe layer concept allowed us to selectively monitor the local structure and magnetism of the Fe(0 0 1) monolayer in a coupled state. The dependence of the monolayer hyperfine parameters on temperature and spacer thickness was determined from the fitted GI-NRS time spectra, collected for the selected thickness of the stepped Au spacer. The influence of the coupling on the hyperfine magnetic field B HF was negligible at temperatures much lower than T C of the uncoupled Fe monolayer ( T C = 210 K as checked by MOKE). The analysis of the time-spectra accumulated at 200 K showed a non-monotonous dependence of the average B HF as a function of the spacer thickness, related to IEC oscillations. The maximum influence of IEC on B HF (13 T) was found for the 4 ML Au spacer.

Grazing-Incidence Small Angle X-ray Scattering (GISAXS) and X-Ray Photon Correlation Spectroscopy (XPCS) studies of island growth in two different systems are presented: 5 ML of iron on MgO(001) and 10 ML of iron on Au(001). Due to a missing conducting surface Fe/MgO thinner than approximately 20 ML could not be studied previously by common methods like STM. Fe/Au(001) is interesting as atoms of gold diffuse easily through iron layers and form precipitates. The coarsening dynamics of these precipitates is investigated by XPCS in GISAXS geometry. Their growth depends on the crystallographic directions of the substrate and correlates with the morphology measured by STM microscopy. Measurements were performed at the ESRF in Grenoble.

The structural and magnetic properties of ultrathin FeO(111) films on Pt(111) with thicknesses from 1 to 16 monolayers (ML) were studied using the nuclear inelastic scattering (NIS) of synchrotron radiation. Distinct evolution of vibrational characteristics with thickness that is revealed in the phonon density of states (PDOS) witnesses a textbook transition from 2D to 3D lattice dynamics. For the thinnest films of 1 and 2 ML, the low energy part of the PDOS followed a linear dependence in energy that is characteristic for 2-dimensional systems. This dependence gradually transforms with thickness to the bulk ~E-square relation. Density functional theory phonon calculations perfectly reproduced the measured 1 ML PDOS within a simple model of a pseudomorphic FeO/Pt(111) interface. The calculations show that the 2D PDOS character is due to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of the vibrational properties with an increasing thickness is closely related to a transient long range magnetic order and stabilization of an unusual structural phase.

The adsorption of MgO molecules on a Fe(001) surface was studied using density functional theory (DFT) and projector augmented wave methods. The energetically most favored configurations for different adsorption sites considered were identified. The most preferable adsorption geometry is when the MgO molecules are parallel to the surface, with Mg in the interstitial site and O in on-top of the Fe atom. During the adsorption of subsequent MgO molecules in this geometry, a sharp, non-oxidized interface is formed between the MgO adlayer and Fe(001) surface. The adsorption of MgO perpendicular to the surface, with oxygen incorporated in the topmost Fe layer is less probable, but may lead to the formation of the FeO layer when stabilized with an excess of oxygen atoms. Structural, electronic and magnetic properties of both interface types were examined for the MgO coverage from 1/9 to 1 monolayer (ML). Electronic and magnetic properties are sensitive to the MgO coverage. For lower coverage of MgO, clear hybridization between the Fe 3d and O 2p states is shown. The average magnetic moment of the surface Fe atoms is reduced with coverage, achieving 2.78 $\mu_{\rm B}$ for 1 ML of MgO., Comment: 9 pages, 7 figures

Magnetization and electrical resistivity measurements have been performed on a stoichiometric single crystalline magnetite Fe 3 O 4 thin film (thickness of ca. 500 nm) MBE deposited on MgO (1 0 0) substrate. The aim of these studies was to check the influence of preparation method and sample form (bulk vs. thin film) on magnetic anisotropy properties in magnetite. The film magnetization along 〈0 0 1〉 versus applied magnetic field has been determined both in the direction parallel and perpendicular to the film surface, and at temperatures above and below the Verwey transition. We have found, in agreement with published results, that the in-plane field of 10 kOe was not sufficient to saturate the sample. This can be understood if some additional factor, on top of the bulk magnetocrystalline anisotropy, is taken into account.

The valence band photoemission spectra of epitaxially grown film and bulk single crystal of magnetite were measured by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at 300 K and 120 K. Four main features of the electron photoemission were observed at about -1.0 eV, -3.5 eV, -5.0 eV and -6.5 eV below the chemical potential; they are rather strongly dependant on structure and preparation of surface. The three higher-energy features showed significant energy dispersion. The ARUPS spectra were compared to the accessible band structure calculations. Special attention was paid to the leading edge of the emission at -1.0 eV of the low-temperature spectrum where an insulating gap should be observed.

The properties of thin films are directly connected with the atomic structure. At elevated temperatures this structure is determined by atomic dynamics. Pronounced effects are expected for thin films of low coverage. We have investigated electronic and dynamical properties of a submonolayer Fe film on a W(1 1 0) substrate with nuclear resonance scattering (NRS) in grazing–incidence geometry. This atomistic technique is best suited for such investigations due to its element (isotopic) and submonolayer sensitivity as demonstrated in the model system of Fe/W(1 1 0). A simple relaxation model was used to explain the temperature dependence of the NRS spectra. The relaxation rates and diffusion coefficients have been calculated. � 2004 Elsevier B.V. All rights reserved.

Ultrathin (8 and 16 � epitaxial Co films were grown on Au(0 0 1)-hex substrates. The films were characterized in situ by LEED, STM and the directional Auger electron spectroscopy (DAES) and ex situ by magnetooptic Kerr effect. From LEED and DAES data it was found that a distorted bcc-Co phase can be stabilized on Au(0 0 1)-hex at least up to 10 ML. The easy axis of magnetization for the bcc-Co films coated with Au lies in-plane along a AE 10 0ae direction. � 2004 Elsevier B.V. All rights reserved.

Epitaxial Fe3O4(001)/MgO(001) films obtained by reactive molecular beam epitaxy were studied using a combination of in situ scanning tunneling microscopy (STM) and monolayer 57Fe probe Conversion E...

The Kerr magnetometer with differential amplifier which in contrast to lock-in detection technique, is especially recommended for rapid measurements up to 1.5 kHz is described. The calibration of the Kerr rotation angle was performed on the standard sputtered films (with thickness from 2 nm to 50 nm) and Fe-wedge sample, prepared by MBE-technique, in the range of thickness from 1ML to 50 ML of Fe. The test measurements on spin valve structure were also performed.

The development of the low energy muon beam at PSI opens the possibility of studying muon diffusion in artificially layered structures within the nm scale. Here, we report on first muon diffusion experiments on different Cr=x nm Au=Cr trilayers ðx ¼ 19; 21; 30; 39Þ in the temperature range from 5 to 320 K: If the appropriate implantation energy is chosen, the initial muon implantation profile is centered within the non-magnetic Au layer. Muons stopping in magnetic Cr or penetrating the Au/Cr interface by thermally activated diffusion immediately lose their spin polarization. The depolarization of the LE-mSR signal allows extraction of the time-dependent fraction of muons reaching one of the interfaces. r 2002 Elsevier Science B.V. All rights reserved.

Epitaxial Fe(001) films of a high crystalline and surface quality, as checked in situ with Auger electron spectroscopy, low energy electron diffraction and STM, were grown on MgO(001). Such films show an exceptional corrosion resistance remaining metallic for years at the ambient atmosphere, except of a 5 10 nm surface layer, as found using the conversion electron Mossbauer spectroscopy (GEMS). For more systematic corrosion studies, 50 nm iron films were prepared of the 57 Fe isotope. As-prepared Fe films, exposed to the atmosphere did not show clear morphological and compositional changes, which could be associated with the oxide formation, as checked with contact AFM in air and with CEMS. After exposure of the film to HNO 3 or HCl vapors corrosion was observed with AFM. It resulted in two different types of surface modifications. The first one was seen as a homogenous granular layer with the height amplitude of about 15 nm. Corrosion-induced changes of the second type have a localized character resulting in micrometer sized porous protrusions. The corrosion products were identified as γ-FeOOH. Controlled oxidation of a surface iron layer to epitaxial Fe 3 O 4 passivated the film.

Annealed 10 ML Fe films on Au(0 0 1) were studied using STM. Annealing above 670 K causes violent changes of the surface due to Au segregation. At 800 K annealing, formation of nanometer sized plate-like precipitates of gold in the Fe layer is observed. At higher temperatures the precipitates migrate and agglomerate.

Structural and magnetic properties of ultrathin Co films were studied by scanning tunneling microscopy and magneto-optics. Hundred nm Au(1 1 1) films grown epitaxially on mica were used as buffer layers. The initial Co nucleation at the elbows of the ‘‘herringbone’’ reconstruction determined the film morphology, which displayed long chains resulting from the coalescence of the self-organized Co nuclei. A height amplitude of the chains changed considerably upon film annealing. For the ex situ magnetic measurements, wedge samples were prepared, protected with a 5 nm Au layer. Using Kerr magnetometry it was possible to observe the spin reorientation transition. It turned out that the critical thickness decreases for annealed films. The magnetic surface anisotropy was determined and correlated with the film microstructure. 2002 Elsevier Science B.V. All rights reserved.

The access to X-rays of third generation synchrotron radiation sources enables studies of dynamics in metallic systems in grazing incidence geometry. Combining grazing incidence reflection of X-rays with nuclear resonant scattering of synchrotron radiation allows depth-selective investigations of hyperfine parameters and diffusion phenomena of iron and iron compounds. The unique feature of this method is its sensitivity to near-surface motions of atoms and not exclusively to the atoms on the surface. The depth sensitivity can be varied between about two and more than 10 nm. A 300 nm thick 57 Fe sample grown by molecular beam epitaxy on a cleaved MgO(0 0 1) substrate was investigated. The diffusion coefficient of iron in the near-surface layer (thickness about 2 nm) is almost two orders of magnitude larger than in bulk bcc iron at the same temperature.

Resent results concerning epitaxial Fe 3 O 4 (001) films grown by reactive deposition on MgO(001) substrates as well as obtained by oxidation of epitaxial Fe(001) films are reviewed. Conversion electron Mossbauer spectroscopy (CEMS) performed in and ex situ was used to check the stoichiometry and electronic properties with monolayer resolution. Size effects were reflected in reduction of the Verwey temperature for the film thickness less than 50 nm. With further decrease in thickness, the films showed strong deviation from the bulk properties due to formation of a magnesium rich phase near the MgO/Fe 3 O 4 interface. Surface oxidation to γ-Fe 2 O 3 , which can be reversed by annealing, was found using CEMS. The atomic scale surface characterization was accomplished for the first time in situ by the scanning tunneling microscopy, which revealed details of the surface reconstruction and termination.

Ultrathin cobalt films and wedges in gold envelope Au/Co(d Co 0) were determined for samples with different thicknesses. Annealing induced in the sample: (i) flattening of the cobalt surface; (ii) a decrease of the coercivity field and magnetic anisotropy caused a decrease of thickness of reorientation from easy axis state to easy plane one; (iii) an increase of the Barkhausen volume which contains many cobalt islands creating the chains. Approaching the reorientation region, the character of the magnetization reversal drastically changes from that with the preference of domain wall propagation into the one connected to the domain wall nucleation.

Ultrathin Fe(001) films, of 1-3 atomic layers, were grown on the Au(001)-hex surface by molecular beam epitaxy. The film growth was controlled in situ by LEED and STM. At the initial stages of the iron growth, a monolayer of Au automatically diffuses onto the growing Fe film, preventing it from breaking up into islands. Conversion electron Mossbauer spectroscopy (CEMS) reveals considerable Au-Fe intermixing at the interface, which leads to formation of a two-dimensional alloy. The intermixing is also responsible for certain deterioration of the atomic order and the layer sequence in the artificial FeAu alloy obtained by alternative deposition of Fe(001) and Au(001) monolayers. CEMS data for single Fe films and Fe-Au monoatomic superlattices are compared and discussed basing on the FLAPW calculations using WIEN97 code.

Molecular beam epitaxy grown (001) oriented Cr/Fe/Cr and Cr/Fe/Cr/Fe/Cr sandwiches were characterized using the conversion electron Mossbauer spectroscopy (CEMS), which proved that the FeCr interface extended up to about 2.5 atomic layers. Analysis of the CEMS results was based on a simple alloy-model of the Fe/Cr interface, resulting in concentration profiles of Fe and Cr atoms. The derived interface model was then used to study the effect of thermal annealing on the film properties. The CEMS studies were correlated with the measurements of the indirect exchange coupling followed by the magneto-optic Kerr effect. Whereas CEMS revealed a measurable effect of annealing on the interface atomic structure for the annealing temperature T A = 200°C, the coupling character began to change at considerably higher temperature (about 400 °C).

γ-ray holography is a novel method for three-dimensional (3D) imaging of a local atomic structure, which utilizes the internal reference idea of holography. The principles of this method will be presented with emphasis on the phase information gained by means of complex holograms.

Metal-oxide ${\mathrm{[Fe}}_{K}/(\text{MgO}){}_{L}{\mathrm{]}}_{N}$ multilayers were grown on MgO(001) substrates for various integer numbers $(K,L)$ of the Fe(001) and MgO(001) monolayers, respectively, and the number of repetitions $N$ varied from 6 to 30. Room-temperature conversion electron M\"ossbauer spectroscopy (CEMS) measurements proved that the magnetic properties of these monoatomic multilayers were extremely sensitive to both the Fe and MgO sublayer thicknesses. A stable ferromagnetic state and a strong perpendicular magnetization component at room temperature were obtained by changing the sublayer thickness and the number of multilayer repetitions. The analysis of the CEMS spectra in correlation with the magneto-optic Kerr effect measurements indicated a complicated domain structure in this special type of metal-insulator material. The vortexlike domain structure was confirmed by micromagnetic simulations.

The (1 0 0) surface of the magnetite thin film has been investigated by low-energy ion scattering in the small-angle geometry and in the temperature range of 85–300 K. Thin film of Fe3O4 was grown on MgO (1 0 0) substrate by the molecular beam epitaxy (MBE) and characterized by low-energy electron diffraction, conversion electron Mossbauer spectroscopy and scanning tunneling microscopy. The scattered ion spectra have shown two maxima, in which the intensity of the maximum at low-energy side increases enormously with increasing bombarding energy values. The temperature dependence of scattering ion yield, R+(T), for 5.0, 5.5 and 6.0 keV Ne+ bombardments exhibit two minima, around 110 K and around 125 K, related to the metal-insulator phase transition of this material. The high-temperature minimum was found to disappear at 6.5 keV Ne+ bombardment, indicating the ion velocity dependence of the character of the R+(T) curve, which has been observed previously for the MBE (1 1 1) magnetite thin film. This phenomenon has been explained in the framework of the resonant and Auger neutralization.

Conversion electron Mossbauer spectroscopy (CEMS) was applied to model the buried interfaces in epitaxial 1–14 monolayer (ML) Fe(0 0 1) films sandwiched between Cr(0 0 1) layers. The local arrangement of Fe and Cr was derived by analysis of the experimental hyperfine field distributions determined from 80 K CEMS spectra. A discontinuity in magnetic properties for the 6 ML Fe film suggests that a modification of the magnetic structure occurs at this thickness. The 57 Fe probe layer analysis showed that Cr/Fe and Fe/Cr interfaces are non-equivalent. The lower interface showed up to be smoother than the upper one. The Fe concentration profile obtained form the CEMS analysis displayed a considerable interface Fe–Cr alloying for films deposited at the room temperature.

Epitaxial Fe3O4(0 0 1) thin films were grown on MgO(0 0 1) using molecular beam of 57Fe at the oxygen partial pressure of about 1×10−6 mbar. LEED patterns indicated perfect growth with a p(1×1) reconstructed surface (as labeled with respect to the bulk unit cell of magnetite) . In situ UHV conversion electron Mossbauer spectroscopy (CEMS) was applied to investigate the film stoichiometry and composition. CEMS spectra taken for films in the 10 nm range revealed a magnesium rich magnetite MgxFe3−xO4 phase formed at the MgO/Fe3O4 interface. Ex situ Mossbauer measurements proved that the magnetite surface oxidizes when exposed to the atmosphere for a couple of weeks. The oxidized phase was identified as a few nanometers thick surface layer of γ-Fe2O3 formed on Fe3O4. By virtue of the γ-Fe2O3 CEMS pattern, the oxidation can be easily misinterpreted as a surface non-stoichiometry for films studied only ex situ. The oxidation process is reversible and annealing at 600 K in UHV restores the magnetite surface structure. At elevated annealing temperature Fe also diffuses into MgO forming a wustite phase.

The possibility of imaging the local environments of nuclei with different hyperfine interaction parameters using complex γ -ray holography is investigated. The discussion is based on calculations performed for magnetite Fe3O4, in which Fe ions occupy two nonequivalent positions in the unit cell characterized by different sets of hyperfine interaction parameters.

Exchange bias (EB) is studied in an epitaxial CoO/Fe bilayer grown by molecular beam epitaxy on MgO(001). The characterization of the layer structure and interface quality was performed using LEED, AES and conversion electron Mossbauer spectroscopy(CEMS). Detailed experimental studies of the EB effect as a function of temperature were carried out using the magneto-optical Kerr effect. Notwithstanding the formation of Fe oxides at the CoO/Fe interface, as evidenced by the CEMS measurements, we observed a negative EB with blocking temperature T B = 257 K. At temperatures close to T B , the coercive field reaches a maximum, which is in agreement with the stiles and McMichael model.

Low-energy muon spin rotation (LE-μ+SR) measurements were performed on 3.4 and 9.1 nm epitaxial Cr(0 0 1) films buried by non-magnetic boundary layers to study the collapse of the spin-density wave (SDW) of bulk Cr, which is expected when decreasing the thickness of the film below the modulation period of the SDW ( ≈6 nm ). Magnetic phases of Cr are identified by the fast relaxation of the muon spin polarization. While a reduced Neel temperature of 285 K with respect to the bulk value is found for the 9.1 nm Cr layer, the 3.4 nm film remains in a magnetic phase over the investigated temperature range of 20–320 K.

A giant magneto-optical anisotropy (MOA) in a magnetic monoatomic Fe/Au multilayer structure is reported. The dependence of the off-diagonal part of the optical conductivity tensor on the angle between the magnetization and crystallographic axes is evidenced by measurements of both the polar and longitudinal Kerr effects. The microscopic origin of the MOA is elucidated on the basis of the first principles’ band-structure calculations. A relationship of the MOA with the predicted strong anisotropy of Fe d orbital magnetic moment and the magnetocrystalline anisotropy is discussed.

The (1 1 1) surface of the magnetite thin film has been investigated by low-energy ion scattering (LEIS) in the small-angle geometry and in the temperature range 85–300 K. The thin film has been grown by molecular beam epitaxy (MBE) and characterized by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and conversion electron Mossbauer spectroscopy (CEMS). The temperature dependence of the scattered ion yield, R + ( T ), obtained by LEIS technique has shown anomaly around 120 K attributed to the insulator–metallic phase transition of this material. The character of the R + ( T ) curve has been found to depend on the velocity of incoming ions. The resonant and Auger neutralization, which depends on the density of state and on the degree of electron localization, can be responsible for the behavior of the R + ( T ) curve, especially in the phase transition region.

Thin magnetite films grown on cleaved MgO (100) substrates were studied by in-situ conversion electron Mossbauer spectroscopy (CEMS) in the temperature range of 80 K–300 K. The film growth was monitored by low energy electron diffraction revealing a perfect epitaxy in the whole thickness range from 430 nm down to 3 nm. CEMS measurements proved an ideal magnetite stoichiometry of the 430 nm thick film reflected both in the hyperfine pattern and in the Verwey transition. The thinner films showed strong deviation from the bulk properties, which was attributed to the modification of composition at the MgO/Fe3O4 interface, at which a magnesium rich phase is supposed based on CEM spectra. This phase, which was not observed previously, could be detected thanks to highly sensitive low-temperature measurements.