285 research outputs found
Synthesis, crystal structure and chemical stability of the superconductor FeSe_{1-x}
We report on a comparative study of the crystal structure and the magnetic
properties of FeSe1-x (x= 0.00 - 0.15) superconducting samples by neutron
powder diffraction and magnetization measurements. The samples were synthesized
by two different methods: a 'low-temperature' one using powders as a starting
material at T =700 C and a "high-temperature' method using solid pieces of Fe
and Se at T= 1070 C. The effect of a starting (nominal) stoichiometry on the
phase purity of the obtained samples, the superconducting transition
temperature Tc, as well as the chemical instability of FeSe1-x at ambient
conditions were investigated. It was found that in the Fe-Se system a stable
phase exhibiting superconductivity at Tc~8K exists in a narrow range of
selenium concentration (FeSe0.974(2)).Comment: 7 pages, 7 figures, 1 tabl
Direct observation of the ground state of a 1/3 quantum magnetization plateau in SrMnPO using neutron diffraction measurements
We can directly investigate the ground state in magnetization-plateau fields
(plateau ground state) using neutron diffraction measurements. We performed
neutron diffraction measurements on the spin-5/2 trimer substance
SrMnPO in magnetization-plateau fields. The integrated
intensities of magnetic reflections calculated using an expectation value of
each spin in a plateau ground state of an isolated-trimer model agree well with
those obtained experimentally in the magnetization-plateau fields. We succeeded
in direct observation of a plateau ground state in SrMnPO
Anomalous pressure dependence of the atomic displacements in the relaxor ferroelectric PbMgTaO
The crystal structure of the PbMgTaO (PMT) relaxor
ferroelectric was studied under hydrostatic pressure up to GPa by
means of powder neutron diffraction. We find a drastic pressure-induced
decrease of the lead displacement from the inversion centre which correlates
with an increase by 50 % of the anisotropy of the oxygen temperature
factor. The vibrations of the Mg/Ta are, in contrast, rather pressure
insensitive. We attribute these changes being responsible for the previously
reported pressure-induced suppression of the anomalous dielectric permittivity
and diffuse scattering in relaxor ferroelectrics
Candidate Quantum Spin Liquid in the Ce\textsuperscript{3+} Pyrochlore Stannate CeSnO
We report the low temperature magnetic properties of CeSnO, a
rare-earth pyrochlore. Our susceptibility and magnetization measurements show
that due to the thermal isolation of a Kramers doublet ground state,
CeSnO has Ising-like magnetic moments of
. The magnetic moments are confined to the local trigonal axes,
as in a spin ice, but the exchange interactions are antiferromagnetic. Below 1
K the system enters a regime with antiferromagnetic correlations. In contrast
to predictions for classical -Ising spins on the
pyrochlore lattice, there is no sign of long-range ordering down to 0.02 K. Our
results suggest that CeSnO features an antiferromagnetic liquid
ground state with strong quantum fluctuations.Comment: 6 pages, 4 figure
Absence of Long Range Magnetic Order in the La1.4Sr0.8Ca0.8Mn2O7 Bilayered Manganite
In this work we studied, by means of high-resolution neutron diffraction as a
function of temperature, the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite for two
different annealing treatments. Out data allowed us to shown, for the first
time, the absence of long-range magnetic order in this optimally doped
bilayered manganite where the A-site of the structure is doped with equal
proportions of different isovalent cations (Ca and Sr). The system, however,
presents defined IM transitions which suggest that the transport properties are
not linked to the evolution of long-range order and that two dimensional spin
ordering in the layers of the perovskite blocks may be sufficient to 'assist'
the hole hopping. Possible reason for the suppression of magnetic order induced
by the Ca doping is a size effect coupled to the cation size mismatch between
the Sr and Ca ions.Comment: 24 pages, 7 figure
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