217 research outputs found
Studies of local magnetism and local structure in La(2-x)Sr(x)CuO4
The muon spin rotation (MUSR) study of local magnetism of Sr-doped La2CrO4 is reviewed. Emphasis is placed on magnetic order as detected by local and bulk probes with local atomic environments studies by x ray absorption fine structure (XAFS). Correlations between the MUSR study of local magnetic ordering and the bulk magnetization study are presented along with a discussion of the dependence upon oxygen stoichiometry. Results are presented for both superconducting phases and magnetic phases. Recent data which reveals the existence of local magnetic ordering in the hydrogen-doped YBa2Cu3O7 system are also discussed
Supporting flight data analysis for Space Shuttle Orbiter experiments at NASA Ames Research Center
The space shuttle orbiter experiments program is responsible for collecting flight data to extend the research and technology base for future aerospace vehicle design. The infrared imagery of shuttle (IRIS), catalytic surface effects, and tile gap heating experiments sponsored by Ames Research Center are part of this program. The software required to process the flight data which support these experiments is described. In addition, data analysis techniques, developed in support of the IRIS experiment, are discussed. Using the flight data base, the techniques provide information useful in analyzing and correcting problems with the experiment, and in interpreting the IRIS image obtained during the entry of the third shuttle mission
Direct Evidence for the Source of Reported Magnetic Behavior in "CoTe"
In order to unambiguously identify the source of magnetism reported in recent
studies of the Co-Te system, two sets of high-quality, epitaxial CoTe films
(thickness 300 nm) were prepared by pulse laser deposition (PLD).
X-ray diffraction (XRD) shows that all of the films are epitaxial along the
[001] direction and have the hexagonal NiAs structure. There is no indication
of any second phase metallic Co peaks (either or ) in the XRD
patterns. The two sets of CoTe films were grown on various substrates with
PLD targets having Co:Te in the atomic ratio of 50:50 and 35:65. From the
measured lattice parameters for the former and
for the latter, the compositions CoTe (63.1% Te) and CoTe
(63.8% Te), respectively, are assigned to the principal phase. Although XRD
shows no trace of metallic Co second phase, the magnetic measurements do show a
ferromagnetic contribution for both sets of films with the saturation
magnetization values for the CoTe films being approximately four times
the values for the CoTe films. Co spin-echo nuclear magnetic
resonance (NMR) clearly shows the existence of metallic Co inclusions in the
films. The source of weak ferromagnetism reported in several recent studies is
due to the presence of metallic Co, since the stoichiometric composition "CoTe"
does not exist.Comment: 19 pages, 7 figure
Local Structure and It's Effect on The Ferromagnetic Properties of LaSrCoO thin films}
We have used high-resolution Extended X-ray Absorption Fine-Structure and
diffraction techniques to measure the local structure of strained
LaSrCoO films under compression and tension. The lattice
mismatch strain in these compounds affects both the bond lengths and the bond
angles, though the larger effect on the bandwidth is due to the bond length
changes. The popular double exchange model for ferromagnetism in these
compounds provides a correct qualitative description of the changes in Curie
temperature , but quantitatively underestimates the changes. A microscopic
model for ferromagnetism that provides a much stronger dependence on the
structural distortions is needed.Comment: 4 pages, 4 figure
Flux pinning and phase separation in oxygen rich La2-xSrxCuO4+y system
We have studied the magnetic characteristics of a series of super-oxygenated
La2-xSrxCuO4+y samples. As shown in previous work, these samples spontaneously
phase separate into an oxygen rich superconducting phase with a TC near 40 K
and an oxygen poor magnetic phase that also orders near 40 K. All samples
studied are highly magnetically reversible even to low temperatures. Although
the internal magnetic regions of these samples might be expected to act as
pinning sites, our present study shows that they do not favor flux pinning.
Flux pinning requires a matching condition between the defect and the
superconducting coherence length. Thus, our results imply that the magnetic
regions are too large to act as pinning centers. This also implies that the
much greater flux pinning in typical La2-xSrxCuO4 materials is the result of
nanoscale inhomogeneities that grow to become the large magnetic regions in the
super-oxygenated materials. The superconducting regions of the phase separated
materials are in that sense cleaner and more homogenous than in the typical
cuprate superconductor.Comment: 4 figures 8 pages Submitted to PR
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