132 research outputs found
BaFe2As2/Fe bilayers with [001]-tilt grain boundary on MgO and SrTiO3 bicrystal substrates
Co-doped BaFe2As2 (Ba-122) can be realized on both MgO and SrTiO3 bicrystal
substrates with [001]-tilt grain boundary by employing Fe buffer layers.
However, an additional spinel (i.e. MgAl2O4) buffer between Fe and SrTiO3 is
necessary since an epitaxial, smooth surface of Fe layer can not be grown on
bare SrTiO3. Both types of bicrystal films show good crystalline quality.Comment: Accepted for the ISS2012 Proceedins, a special issue of Physics
Procedi
Hall-plot of the phase diagram for Ba(Fe1-xCox)2As2
The Hall effect is a powerful tool for investigating carrier type and
density. For single-band materials, the Hall coefficient is traditionally
expressed simply by , where is the charge of the carrier,
and is the concentration. However, it is well known that in the critical
region near a quantum phase transition, as it was demonstrated for cuprates and
heavy fermions, the Hall coefficient exhibits strong temperature and doping
dependencies, which can not be described by such a simple expression, and the
interpretation of the Hall coefficient for Fe-based superconductors is also
problematic. Here, we investigate thin films of Ba(FeCo)As
with compressive and tensile in-plane strain in a wide range of Co doping. Such
in-plane strain changes the band structure of the compounds, resulting in
various shifts of the whole phase diagram as a function of Co doping. We show
that the resultant phase diagrams for different strain states can be mapped
onto a single phase diagram with the Hall number. This universal plot is
attributed to the critical fluctuations in multiband systems near the
antiferromagnetic transition, which may suggest a direct link between magnetic
and superconducting properties in the BaFeAs system.Comment: Accepted for publication in Scientific Reports, 6 main figures plus
Supplemental Information (8 figures
CT-Based Attenuation Correction in I-123-Ioflupane SPECT
Purpose Attenuation correction (AC) based on low-dose computed tomography (CT)
could be more accurate in brain single-photon emission computed tomography
(SPECT) than the widely used Chang method, and, therefore, has the potential
to improve both semi-quantitative analysis and visual image interpretation.
The present study evaluated CT-based AC for dopamine transporter SPECT with
I-123-ioflupane. Materials and methods Sixty-two consecutive patients in whom
I-123-ioflupane SPECT including low-dose CT had been performed were recruited
retrospectively at 3 centres. For each patient, 3 different SPECT images were
reconstructed: without AC, with Chang AC and with CT-based AC. Distribution
volume ratio (DVR) images were obtained by scaling voxel intensities using the
whole brain without striata as reference. For assessing the impact of AC on
semi-quantitative analysis, specific-to-background ratios (SBR) in caudate and
putamen were obtained by fully automated SPM8-based region of interest (ROI)
analysis and tested for their diagnostic power using receiver-operator-
characteristic (ROC) analysis. For assessing the impact of AC on visual image
reading, screenshots of stereotactically normalized DVR images presented in
randomized order were interpreted independently by two raters at each centre.
Results CT-based AC resulted in intermediate SBRs about half way between no AC
and Chang. Maximum area under the ROC curve was achieved by the putamen SBR,
with negligible impact of AC (0.924, 0.935 and 0.938 for no, CT-based and
Chang AC). Diagnostic accuracy of visual interpretation also did not depend on
AC. Conclusions The impact of CT-based versus Chang AC on the interpretation
of I-123-ioflupane SPECT is negligible. Therefore, CT-based AC cannot be
recommended for routine use in clinical patient care, not least because of the
additional radiation exposure
High field superconducting properties of Ba(Fe1-xCox)2As2 thin films
The film investigated grew phase-pure and highly textured with in-plane and out-of-plane full width at half maximum, FWHM, of = 0.74° and = 0.9°, Suppl. S1. The sample, however, does contain a large density of ab-planar defects, as revealed by transition electron microscope (TEM) images of focused ion beam (FIB) cuts near the microbridges, Fig. 1. These defects are presumably stacking faults (i.e. missing FeAs layers)20. The reason for this defect formation (also observed on technical substrates)21 is not fully understood. Possible reasons are a partial As loss during deposition22, and relaxation processes in combination with the Fe buffer layer23. Estimating the distance between these intergrowths leads to values varying between 5 and 10 nm. Between the planar defects, an orientation contrast is visible in TEM (inset Fig. 1b), i.e. the brighter crystallites are slightly rotated either around (010) (out-of-plane spread, ) or around (001) (in-plane spread, ) and enclosed by dislocation networks or small-angle GBs. Since the crystallites are sandwiched between planar defects, an in-plane misorientation is most likely. The out-of-plane misorientation, on the other hand, is visible as a slight tilt of the ab-planar defects with respect to each other, especially in the upper part of the sample. No globular or columnar precipitates were found
- âŠ