742 research outputs found
Evidence for electromagnetic granularity in polycrystalline Sm1111 iron-pnictides with enhanced phase purity
We prepared polycrystalline SmFeAsO1-xFx (Sm1111) bulk samples by sintering
and hot isostatic pressing (HIP) in order to study the effects of phase purity
and relative density on the intergranular current density. Sintered and HIPped
Sm1111 samples are denser with fewer impurity phases, such as SmOF and the
grain boundary wetting phase, FeAs. We found quite complex magnetization
behavior due to variations of both the inter and intragranular current
densities. Removing porosity and reducing second phase content enhanced the
intergranular current density, but HIPping reduced Tc and the intragranular
current density, due to loss of fluorine and reduction of Tc. We believe that
the HIPped samples are amongst the purest polycrystalline 1111 samples yet
made. However, their intergranular current densities are still small, providing
further evidence that polycrystalline pnictides, like polycrystalline cuprates,
are intrinsically granular.Comment: 14 pages, 6 figure
Influence of growth temperature on the vortex pinning properties of pulsed laser deposited YBa(2)Cu(3)O(7-x) thin films
Epitaxial high-temperature superconducting YBa(2)Cu(3)O(7-x) thin films grown on 2 degrees miscut (001) (LaAlO(3))(0.3)-(SrAl(0.5)Ta(0.5)O(3))(0.7) substrates by pulsed laser deposition show significant and systematic changes in flux pinning properties on changing the substrate temperature from 730 to 820 degrees C. The bulk pinning force is highest for the 760 degrees C growth, rising to a maximum of 4.4 GN/m(3) at 77 K, though there are indications that vortex pinning strength is even higher for the 730 degrees C growth once allowance for the current-blocking effects of a-axis oriented grains is made. Cross-sectional transmission electron microscope images show that the density of antiphase boundaries, stacking faults, and edge dislocations increases strongly with decreasing growth temperature, and is highest at 730 degrees C. In spite of the enhanced density of the pinning defects mentioned above, their vortex pinning effect is still much smaller than for insulating nanoparticles of high density and optimum size, where pinning forces can be four to five times higher.open121
Search for dinucleon decay into pions at Super-Kamiokande
A search for dinucleon decay into pions with the Super-Kamiokande detector
has been performed with an exposure of 282.1 kiloton-years. Dinucleon decay is
a process that violates baryon number by two units. We present the first search
for dinucleon decay to pions in a large water Cherenkov detector. The modes
O C, O
N, and O
O are investigated. No significant excess in the
Super-Kamiokande data has been found, so a lower limit on the lifetime of the
process per oxygen nucleus is determined. These limits are:
years,
years, and
years. The lower
limits on each mode are about two orders of magnitude better than previous
limits from searches for dinucleon decay in iron.Comment: 20 pages, 17 figures. Accepted for publication in Physical Review D
on March 30, 201
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