7,502 research outputs found
Magnetic Properties of the Novel Low-Dimensional Cuprate Na5RbCu4(AsO4)4Cl2
The magnetic properties of a new compound, Na5RbCu4(AsO4)4Cl2 are reported.
The material has a layered structure comprised of square Cu4O4 tetramers. The
Cu ions are divalent and the system behaves as a low-dimensional S=1/2
antiferromagnet. Spin exchange in Na5RbCu4(AsO4)4Cl2 appears to be
quasi-two-dimensional and non-frustrated. Measurements of the bulk magnetic
susceptibility and heat capacity are consistent with low-dimensional magnetism.
The compound has an interesting, low-entropy, magnetic transition at T = 17 K.Comment: 4 pages, 5 figure
Au-SN Flip-Chip Solder Bump for Microelectronic and Optoelectronic Applications
As an alternative to the time-consuming solder pre-forms and pastes currently
used, a co-electroplating method of eutectic Au-Sn alloy was used in this
study. Using a co-electroplating process, it was possible to plate the Au-Sn
solder directly onto a wafer at or near the eutectic composition from a single
solution. Two distinct phases, Au5Sn and AuSn, were deposited at a composition
of 30at.%Sn. The Au-Sn flip-chip joints were formed at 300 and 400 degrees
without using any flux. In the case where the samples were reflowed at 300
degrees, only an (Au,Ni)3Sn2 IMC layer formed at the interface between the
Au-Sn solder and Ni UBM. On the other hand, two IMC layers, (Au,Ni)3Sn2 and
(Au,Ni)3Sn, were found at the interfaces of the samples reflowed at 400
degrees. As the reflow time increased, the thickness of the (Au,Ni)3Sn2 and
(Au,Ni)3Sn IMC layers formed at the interface increased and the eutectic
lamellae in the bulk solder coarsened.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Spin-lattice order in frustrated ZnCr2O4
Using synchrotron X-rays and neutron diffraction we disentangle spin-lattice
order in highly frustrated ZnCrO where magnetic chromium ions occupy
the vertices of regular tetrahedra. Upon cooling below 12.5 K the quandary of
anti-aligning spins surrounding the triangular faces of tetrahedra is resolved
by establishing weak interactions on each triangle through an intricate lattice
distortion. The resulting spin order is however, not simply a N\'{e}el state on
strong bonds. A complex co-planar spin structure indicates that antisymmetric
and/or further neighbor exchange interactions also play a role as ZnCrO
resolves conflicting magnetic interactions
Refined Simulations of the Reaction Front for Diffusion-Limited Two-Species Annihilation in One Dimension
Extensive simulations are performed of the diffusion-limited reaction
AB in one dimension, with initially separated reagents. The reaction
rate profile, and the probability distributions of the separation and midpoint
of the nearest-neighbour pair of A and B particles, are all shown to exhibit
dynamic scaling, independently of the presence of fluctuations in the initial
state and of an exclusion principle in the model. The data is consistent with
all lengthscales behaving as as . Evidence of
multiscaling, found by other authors, is discussed in the light of these
findings.Comment: Resubmitted as TeX rather than Postscript file. RevTeX version 3.0,
10 pages with 16 Encapsulated Postscript figures (need epsf). University of
Geneva preprint UGVA/DPT 1994/10-85
Quantitative study of molecular N_2 trapped in disordered GaN:O films
The structure of disordered GaN:O films grown by ion-assisted deposition is
investigated using x-ray absorption near-edge spectroscopy and Raman
spectroscopy. It is found that between 4 and 21 % of the nitrogen in the films
is in the form of molecular N_2 that interacts only weakly with the surrounding
matrix. The anion to cation ratio in the GaN:O host remains close to unity, and
there is a close correlation between the N_2 fraction, the level of oxygen
impurities, and the absence of short-range order in the GaN:O matrix.Comment: 5 pages, 3 figure
Structural and magnetic study of a dilute magnetic semiconductor: Fe doped CeO2 nanoparticles
This paper reports the effect of Fe doping on the structure and room
temperature ferromagnetism of CeO2 nanoparticles. X-ray diffraction and
selective area electron diffraction measurement reflects that Ce1-xFexO2 (x =
0.0 - 0.07) nanoparticles exhibit single phase nature with cubic structure and
none of the sample showed the presence of any secondary phase. The mean
particle size calculated by using a transmission electron microscopy
measurement was found to increase with increase in Fe content. DC magnetization
measurements performed at room temperature indicates that all the samples
exhibit ferromagnetism. The saturation magnetic moment has been found to
increase with an increase in the Fe content.Comment: 16 Pages, 5 figure, 1 Table, Accepted in JN
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Polyamide Nanocomposites for Selective Laser Sintering
Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high
heat resistance characteristics for a plethora of finished parts that are desired and required
for performance driven applications. It is anticipated that nanomodification of polyamide
11 and 12 will result in enhanced polymer performance, i.e., fire retardancy, high strength
and high heat resistance for polyamide 11 and 12. It is expected that these findings will
expand the market opportunities for polyamide 11 and 12 resin manufacturers.
The objective of this research is to develop improved polyamide 11 and 12 polymers
with enhanced flame retardancy, thermal, and mechanical properties for selective laser
sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into the
polyamide 11 and 12 via twin screw extrusion to provide improved material properties of
the polymer blends. Arkema RILSAN® polyamide 11 molding polymer pellets and
Degussa VESTAMID® L1670 polyamide 12 were examined with three types of
nanoparticles: chemically modified montmorillonite (MMT) organoclays, surface
modified nanosilica, and carbon nanofibers (CNFs) to create polyamide 11 and 12
nanocomposites.
Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM)
were used to determine the degree of dispersion. Injection molded test specimens were
fabricated for physical, thermal, mechanical properties, and flammability tests. Thermal
stability of these polyamide 11 and 12 nanocomposites was examined by TGA.
Mechanical properties such as tensile, flexural, and elongation at break were measured.
Flammability properties were also obtained using the Cone Calorimeter at an external
heat flux of 50 kW/m2. TEM micrographs, physical, mechanical, and flammability
properties are included in the paper. Polyamide 11 and 12 nanocomposites properties are
compared with polyamide 11 and 12 baseline polymers. Based on flammability and
mechanical material performance, selective polymers including polyamide 11
nanocomposites and control polyamide 11 were cryogenically ground into fine powders
and fabricated into SLS parts.Mechanical Engineerin
Anisotropic strains and magnetoresistance of La_{0.7}Ca_{0.3}MnO_{3}
Thin films of perovskite manganite La_{0.7}Ca_{0.3}MnO_{3} were grown
epitaxially on SrTiO_3(100), MgO(100) and LaAlO_3(100) substrates by the pulsed
laser deposition method. Microscopic structures of these thin film samples as
well as a bulk sample were fully determined by x-ray diffraction measurements.
The unit cells of the three films have different shapes, i.e., contracted
tetragonal, cubic, and elongated tetragonal for SrTiO_3, MgO, and LaAlO_3
cases, respectively, while the unit cell of the bulk is cubic. It is found that
the samples with cubic unit cell show smaller peak magnetoresistance than the
noncubic ones do. The present result demonstrates that the magnetoresistance of
La_{0.7}Ca_{0.3}MnO_{3} can be controlled by lattice distortion via externally
imposed strains.Comment: Revtex, 10 pages, 2 figure
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