144,505 research outputs found
Mossbauer spectrometer radiation detector
A Mossbauer spectrometer with high efficiencies in both transmission and backscattering techniques is described. The device contains a sodium iodide crystal for detecting radiation caused by the Mossbauer effect, and two photomultipliers to collect the radiation detected by the crystal. When used in the transmission technique, the sample or scatterer is placed between the incident radiation source and the detector. When used in a backscattering technique, the detector is placed between the incident radiation source and the sample of scatterer such that the incident radiation will pass through a hole in the crystal and strike the sample. Diagrams of the instrument are provided
Mossbauer effect and its applications in materials research
It is generally recognized that in any well behaved metal fatigue failure, the following sequence of events occurs. The application of stress causes the movement of defects already present in the specimen, besides producing new defects. These defects concentrate in the regions of stress concentration. This defect concentration, which precedes crack nucleation and its eventual growth, actually amounts to environmental changes for Mossbauer atoms located in these regions. Changes in the atomic composition of the Mossbauer absorber atom environment are sensed by examining changes in the sensitive parameters of the Mossbauer spectra. A preliminary study of changes in the isomer shift and line width of commercial nonmagnetic steel specimen is reported
LaFeAsOF: A low carrier density superconductor near itinerant magnetism
Density functional studies of 26K superconducting LaFeAs(O,F) are reported.
We find a low carrier density, high density of states, and modest
phonon frequencies relative to . The high leads to proximity to
itinerant magnetism, with competing ferromagnetic and antiferromagnetic
fluctuations and the balance between these controlled by doping level. Thus
LaFeAs(O,F) is in a unique class of high superconductors: high
ionic metals near magnetism.Comment: Shortened published form. Typos correcte
Properties of KCoAs and Alloys with Fe and Ru: Density Functional Calculations
Electronic structure calculations are presented for KCoAs and alloys
with KFeAs and KRuAs. These materials show electronic
structures characteristic of coherent alloys, with a similar Fermi surface
structure to that of the Fe-based superconductors, when the electron count
is near six per transition metal. However, they are less magnetic than the
corresponding Fe compounds. These results are discussed in relation to
superconductivity.Comment: 5 page
Prediction of Room Temperature High Thermoelectric Performance in n-type La(Ru,Rh)4Sb12
First principles calculations are used to investigate the band structure and
the transport related properties of unfilled and filled 4d skutterudite
antimonides. The calculations show that, while RhSb3 and p-type La(Rh,Ru)4Sb12
are unfavorable for thermoelectric application, n-type La(Rh,Ru)4Sb12 is very
likely a high figure of merit thermoelectric material in the important
temperature range 150-300 K.Comment: 3 pages, 3 figures. To appear, Appl. Phys. Let
Electronic structure of Ba(Fe,Ru)2As2 and Sr(Fe,Ir)2As2 alloys
The electronic structures of Ba(Fe,Ru)As and Sr(Fe,Ir)As are
investigated using density functional calculations. We find that these systems
behave as coherent alloys from the electronic structure point of view. In
particular, the isoelectronic substitution of Fe by Ru does not provide doping,
but rather suppresses the spin density wave characteristic of the pure Fe
compound by a reduction in the Stoner enhancement and an increase in the band
width due hybridization involving Ru. The electronic structure near the Fermi
level otherwise remains quite similar to that of BaFeAs. The
behavior of the Ir alloy is similar, except that in this case there is
additional electron doping
Optical properties of cubic and rhombohedral GeTe
Calculations of the optical properties of GeTe in the cubic NaCl and
rhombohedral ferroelectric structures are reported. The rhombohedral
ferroelectric distortion increases the band gap from 0.11 eV to 0.38 eV.
Remarkably, substantial changes in optical properties are found even at high
energies up to 5 eV. The results are discussed in relation to the bonding of
GeTe and to phase change materials based on it
Electronic Structure and Bulk Spin Valve Behavior in CaRuO
We report density functional calculations of the magnetic properties and
Fermiology of CaRuO. The ground state consists of ferromagnetic
bilayers, stacked antiferromagnetically. The bilayers are almost but not
exactly half-metallic. In the ferromagnetic state opposite spin polarizations
are found for in-plane and out-of-plane transport. Relatively high out of plane
conductivity is found for the majority spin, which is relatively weakly
conductive in-plane. In the ground state in-plane quantities are essentially
the same, but the out of plane transport is strongly reduced.Comment: 5 page
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