2,020 research outputs found
Differential thermal analysis and solution growth of intermetallic compounds
To obtain single crystals by solution growth, an exposed primary
solidification surface in the appropriate, but often unknown, equilibrium alloy
phase diagram is required. Furthermore, an appropriate crucible material is
needed, necessary to hold the molten alloy during growth, without being
attacked by it. Recently, we have used the comparison of realistic simulations
with experimental differential thermal analysis (DTA) curves to address both
these problems. We have found: 1) complex DTA curves can be interpreted to
determine an appropriate heat treatment and starting composition for solution
growth, without having to determine the underlying phase diagrams in detail. 2)
DTA can facilitate identification of appropriate crucible materials. DTA can
thus be used to make the procedure to obtain single crystals of a desired phase
by solution growth more efficient. We will use some of the systems for which we
have recently obtained single-crystalline samples using the combination of DTA
and solution growth as examples. These systems are TbAl, PrNiSi,
and YMnAl.Comment: 17 pages, 8 figure
A small sealed Ta crucible for thermal analysis of volatile metallic samples
Differential thermal analysis on metallic alloys containing volatile elements
can be highly problematic. Here we show how measurements can be performed in
commercial, small-sample, equipment without modification. This is achieved by
using a sealed Ta crucible, easily fabricated from Ta tubing and sealed in a
standard arc furnace. The crucible performance is demonstrated by measurements
on a mixture of Mg and MgB, after heating up to 1470. We
also show data, measured on an alloy with composition GdMg, that
clearly shows both the liquidus and a peritectic, and is consistent with
published phase diagram data
Ferroelectric and magnetic properties of Pb(Fe2/3W1/3)O3-based multiferroic compounds with cation order
BiFeO3 and PbTiO3 were introduced to a Sc-modified Pb(Fe2/3W1/3)O3 compound with strong cation order to improve the multiferroic properties. It is found that the degree of cation order decreases as the amount of BiFeO3 or PbTiO3 increases. As a result, the saturation magnetization deteriorates. Solid solutions with BiFeO3 show an increase in both ferroelectric and magnetic transition temperatures. However, the ferroelectric remanent polarization is dramatically suppressed. In contrast, solid solution with PbTiO3 leads to an increase in the ferroelectric transition temperature, a decrease in the magnetic transition temperature, and a significant enhancement of remanent polarization. The composition 0.93[0.79Pb(Fe2/3W1/3)O3–0.21Pb(Sc2/3W1/3)O3]–0.07PbTiO3 shows the optimized properties of Tmax of 208K, Pr of 3.6μC/cm2 between 120 and 210K, TN of 209K, and Ms of 0.23μB/f.u. (3.7emu/g) at 10K under 5T
Electrically-detected magnetic resonance in ion-implanted Si:P nanostructures
We present the results of electrically-detected magnetic resonance (EDMR)
experiments on silicon with ion-implanted phosphorus nanostructures, performed
at 5 K. The devices consist of high-dose implanted metallic leads with a square
gap, into which Phosphorus is implanted at a non-metallic dose corresponding to
10^17 cm^-3. By restricting this secondary implant to a 100 nm x 100 nm region,
the EDMR signal from less than 100 donors is detected. This technique provides
a pathway to the study of single donor spins in semiconductors, which is
relevant to a number of proposals for quantum information processing.Comment: 9 pages, 3 figure
Low-Temperature Rapid Synthesis and Superconductivity of Fe-Based Oxypnictide Superconductors
we were able to develop a novel method to synthesize Fe-based oxypnictide
superconductors. By using LnAs and FeO as the starting materials and a
ball-milling process prior to solid-state sintering, Tc as high as 50.7 K was
obtained with the sample of Sm 0.85Nd0.15FeAsO0.85F0.15 prepared by sintering
at temperatures as low as 1173 K for times as short as 20 min.Comment: 2 pages,2 figures, 1 tabl
Magnetic and thermal properties of the S = 1/2 zig-zag spin-chain compound In2VO5
Static magnetic susceptibility \chi, ac susceptibility \chi_{ac} and specific
heat C versus temperature T measurements on polycrystalline samples of In2VO5
and \chi and C versus T measurements on the isostructural, nonmagnetic compound
In2TiO5 are reported. A Curie-Wiess fit to the \chi(T) data above 175 K for
In2VO5 indicates ferromagnetic exchange between V^{4+} (S = 1/2) moments. Below
150 K the \chi(T) data deviate from the Curie-Weiss behavior but there is no
signature of any long range magnetic order down to 1.8 K. There is a cusp at
2.8 K in the zero field cooled (ZFC) \chi(T) data measured in a magnetic field
of 100 Oe and the ZFC and field cooled (FC) data show a bifurcation below this
temperature. The frequency dependence of the \chi_{ac}(T) data indicate that
below 3 K the system is in a spin-glass state. The difference \Delta C between
the heat capacity of In2VO5 and In2TiO5 shows a broad anomaly peaked at 130 K.
The entropy upto 300 K is more than what is expected for S = 1/2 moments. The
anomaly in \Delta C and the extra entropy suggests that there may be a
structural change below 130 K in In2VO5.Comment: 6 pages, 7 figures, 1 tabl
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