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Bertram F.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | Deiter C.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | Schemme T.,University of Osnabrück | Jentsch S.,University of Osnabrück | Wollschlager J.,University of Osnabrück
Journal of Applied Physics | Year: 2013

Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films. © 2013 AIP Publishing LLC.


Wang X.D.,Zhejiang University | Cao Q.P.,Zhejiang University | Jiang J.Z.,Zhejiang University | Franz H.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | And 8 more authors.
Scripta Materialia | Year: 2011

Structural evolution of an Au-based bulk metallic glass (BMG) after severe plastic deformation (SPD) was investigated. The newly formed glass contains high-density shear bands, a reduced ordering and a concomitant excess free volume. Moreover, it exhibits a less-changed local structure even in the supercooled liquid region, but a reduced thermal stability reflected in an accelerated crystal nucleation and growth process. These results suggest that SPD modifies the atomic structure of BMGs by localized shear band formation, thus producing so-called nanoglasses. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Mikhailova D.,Max Planck Institute for Chemical Physics of Solids | Mikhailova D.,Leibniz Institute for Solid State and Materials Research | Schwarz B.,Leibniz Institute for Solid State and Materials Research | Senyshyn A.,TU Munich | And 14 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We have studied the magnetic properties and crystal structure of Sr 3CoIrO 6 and Sr 3NiIrO 6 as a function of temperature. Two characteristic temperatures, T 1=90 K and T 2=25 K for Sr 3CoIrO 6, and T 1=85 K and T 2=15 K for Sr 3NiIrO 6, were observed. Below T 1 a significant increase of magnetization and below T 2 a weak temperature dependence of magnetization in the field-cooled and practically zero magnetization values in the zero-field-cooled mode were detected for both compounds. The existence of Ir4 + in Sr 3CoIrO 6 was confirmed by an Ir-L III x-ray absorption measurement. Magnetoelastic effects have been observed in the temperature dependence of the lattice parameters of Sr 3CoIrO 6 and Sr 3NiIrO 6. The magnetic structure of Sr 3CoIrO 6 in zero fields can be described as a commensurate modulated antiferromagnet with a propagation vector k=(0,0,1). Neutron powder diffraction with polarized neutrons gave evidence of short-range magnetic order, above and below the magnetic ordering temperature. © 2012 American Physical Society.


Kuschel T.,University of Osnabrück | Becker T.,University of Osnabrück | Bruns D.,University of Osnabrück | Suendorf M.,University of Osnabrück | And 3 more authors.
Journal of Applied Physics | Year: 2011

Thin Co films of different thickness deposited on glass are investigated by magnetooptic Kerr effect to study the uniaxial magnetic anisotropy of these films. The direction of the uniaxial magnetic anisotropy is determined from the azimuthal dependence of the magnetic remanence and differs with increasing thickness of the Co film investigated by x-ray reflectivity. Our experiments reveal that preparation conditions like temperature, deposition rate, or obliqueness of deposition cannot be the reason for this rotation effect of the uniaxial magnetic anisotropy. Also, strain in the substrate and possible textures in the film structure can be excluded as the origin of the magnetic behavior as studied by grazing incidence wide angle x-ray scattering. Thus, probably only the substrate shape in connection with the amorphous or polycrystalline film structure can explain the rotation of the uniaxial magnetic anisotropy. © 2011 American Institute of Physics.


Bertram F.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | Deiter C.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | Hoefert O.,Friedrich - Alexander - University, Erlangen - Nuremberg | Schemme T.,University of Osnabrück | And 4 more authors.
Journal of Physics D: Applied Physics | Year: 2012

Epitaxial ultrathin iron oxide films of different thicknesses were grown by reactive molecular beam epitaxy in 10 -6mbar oxygen atmosphere on MgO(001) single crystal substrates at room temperature. Afterwards, the films were studied by x-ray diffraction, x-ray reflectivity and x-ray photoelectron spectroscopy to provide information regarding film structure as well as chemical composition of the films. Except for a very thin interface layer of subnanometre thickness, the iron oxide films have magnetite stoichiometry and structure and Mg does not diffuse from the substrate into the iron oxide film. The interface layer has a wuestite structure as determined by kinematic diffraction analysis. The magnetite films exhibit very homogeneous thickness while the vertical lattice constant decreases gradually towards its bulk value. © 2012 IOP Publishing Ltd.


Wang X.D.,Zhejiang University | Lou H.B.,Zhejiang University | Bednarcik J.,Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen Synchrotron | Franz H.,Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen Synchrotron | And 3 more authors.
Applied Physics Letters | Year: 2013

The tensile behavior of a Cu46Zr46Al8 bulk metallic glass (BMG) at elevated temperatures has been studied using in situ x-ray diffraction and molecular dynamics simulation. It is demonstrated that excess open volume is generated during elastic deformation and accumulated enough before plastic flow starts. The open volume almost keeps constant during homogeneous deformation, suggesting that a high content of open volume is a key point for developing BMGs with pronounced tensile plasticity. © 2013 American Institute of Physics.


Bertram F.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | Deiter C.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | Pflaum K.,Hamburger Synchrotronstrahlungslabor Am Deutschen Elektronen Synchrotron | Suendorf M.,University Osnabrck | And 2 more authors.
Journal of Applied Physics | Year: 2011

A maghemite (γ- Fe2O3) film of 8.3 nm thickness is epitaxially grown on MgO(001) single crystal substrate by reactive molecular beam epitaxy. Chemical composition and crystal structure of the surface was studied by x-ray photoelectron spectroscopy and low energy electron diffraction, respectively. Afterwards the sample was moved to a heating cell for in situ x-ray diffraction experiments on the post-deposition annealing process in high-vacuum to study structural phase transitions of the iron oxide film. The iron oxide film is reduced with increasing temperature. This reduction occurs in two steps that are accompanied by structural transitions. The first step is a reduction from γ- Fe2O3 to γ- Fe 3O4 at 360°C and the second step is the reduction from Fe3O4 to FeO at 410 °C. © 2011 American Institute of Physics.


Wunderlich F.,TU Dresden | Leisegang T.,TU Dresden | Weissbach T.,TU Dresden | Zschornak M.,TU Dresden | And 9 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

In YMn2 O5, the Mn atoms occupy two nonequivalent Wyckoff sites within the unit cell exhibiting different oxygen coordinations, i.e., the system can be characterized as a mixed-valence compound. For the formation of the orthorhombic crystal structure, Jahn-Teller distortions are assumed to play an important role. In this study, we aimed at the investigation of the crystal structure changes upon the substitution of Mn by the non-Jahn-Teller cation Fe3+. Therefore, we synthesized a series of YMn2-x Fex O5 powder samples with x=0, 0.5, and 1 by a citrate technique. We utilized extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) analysis as well as density-functional theory (DFT) to investigate the two nonequivalent Wyckoff sites within the orthorhombic crystal structure (confirmed for all compositions) occupied by transition-metal atoms. For quantitative determination of structural short-range order, all plausible options of substitution of Fe for Mn are discussed. On the basis of these evaluations, the EXAFS and XANES behavior is analyzed and appropriate crystallographic weights are assigned to the subset of structural models in accordance with the experimental data. From EXAFS analysis, using multiple-scattering theory, we conclude only the 4h Wyckoff site to be occupied by Fe [occupancy refined is (100±3) % in case of x=1]. Furthermore, taking the XANES spectra into account, we are able to verify the EXAFS results and additionally explain the differences in the MnK XANES spectra in dependence on x to be caused by changes in the dipole transitions to 4p final states. From quantitative pre-edge analysis an oxidation number of +4 for the Mn atom for x=1 is determined whereas the Fe valence is shown to be unchanged. Since the substitution process only involves one Wyckoff site, the experimentally observed limit to a maximum amount of x=1 is explained. Additionally, a possible disorder, discussed in the literature, is not proven for our samples. With DFT calculations, the experimental findings are verified on the basis of the total energy of the different possible electronic configurations. Crystal-field effects are identified to be responsible for the site-selective substitution of Fe for Mn. © 2010 The American Physical Society.


Bertram F.,Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen Synchrotron | Deiter C.,Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen Synchrotron | Pflaum K.,Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen Synchrotron | Seeck O.H.,Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen Synchrotron
Review of Scientific Instruments | Year: 2012

A very compact multi purpose high vacuum heating chamber for x-ray scattering techniques was developed. The compact design allows the chamber to be installed on high precision diffractometers which usually cannot support heavy and/or large equipment. The chamber is covered by a Be dome allowing full access to the hemisphere above the sample which is required for in-plane grazing incident x-ray diffraction and out-off plane wide angle x-ray diffraction. © 2012 American Institute of Physics.


PubMed | Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen Synchrotron
Type: Journal Article | Journal: The Review of scientific instruments | Year: 2012

A very compact multi purpose high vacuum heating chamber for x-ray scattering techniques was developed. The compact design allows the chamber to be installed on high precision diffractometers which usually cannot support heavy and/or large equipment. The chamber is covered by a Be dome allowing full access to the hemisphere above the sample which is required for in-plane grazing incident x-ray diffraction and out-off plane wide angle x-ray diffraction.

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