38 research outputs found
Evolution of magnetic and crystal structures in the multiferroic FeTe2O5Br
Neutron diffraction and nuclear quadrupole resonance (NQR) measurements were
employed to investigate magnetic order in the non-ferroelectric phase preceding
the low-temperature multiferroic state in FeTe2O5Br. Refnement of the neutron
diffraction data and simulations of 79,81Br NQR spectra reveal that the
incommensurate magnetic ordering in the non-ferroelectric state comprises
amplitude-modulated magnetic moments, similarly as in the multiferroic state.
The two ordered states differ in the orientation of the magnetic moments and
phase shifts between modulation waves. Surprisingly, all symmetry restrictions
for the electric polarization are absent in both states. The different
ferroelectric responses of the two states are thus argued to arise from the
differences in the phase shifts between certain modulation waves, which cancel
out in the non-ferrolectric state.Comment: 9 pages, 8 figures including appendix, published in PR
Unconventional Magnetism in a Nitrogen-Based Analogue of Cupric Oxide
We have investigated the magnetic properties of CuNCN, the first
nitrogen-based analogue of cupric oxide, CuO. Our muon spin relaxation, nuclear
magnetic resonance and electron spin resonance studies reveal that classical
magnetic ordering is absent down to lowest temperatures. However, large
enhancement of spin correlations and unexpected inhomogeneous magnetism have
been observed below 80 K. We attribute this to a peculiar fragility of the
electronic state against weak perturbations due to geometrical frustration,
which selects between competing spin-liquid and more conventional frozen
states.Comment: 4 pages + 1 page of supplementary information, accepted for
publication in PR
Origin of Tc Enhancement Induced by Doping Yttrium and Hydrogen into LaFeAsO-based Superconductors: 57Fe, 75As, 139La, and 1H-NMR Studies
We report our extensive 57Fe-, 75As-, 139La-, and 1H-NMR studies of
La_{0.8}Y_{0.2}FeAsO_{1-y} (La_{0.8}Y_{0.2}1111) and
LaFeAsO_{1-y}H_{x}(La1111H), where doping yttrium (Y) and hydrogen (H) into
optimally doped LaFeAsO_{1-y} (La1111(OPT)) increases T_c=28 K to 34 and 32 K,
respectively. In the superconducting (SC) state, the measurements of
nuclear-spin lattice-relaxation rate 1/T_1 have revealed in terms of a multiple
fully gapped s_\pm-wave model that the SC gap and T_c in La_{0.8}Y_{0.2}1111
become larger than those in La1111(OPT) without any change in doping level. In
La1111H, the SC gap and T_c also increase slightly even though a decrease in
carrier density and some disorders are significantly introduced. As a
consequence, we suggest that the optimization of both the structural parameters
and the carrier doping level to fill up the bands is crucial for increasing T_c
among these La1111-based compounds through the optimization of the Fermi
surface topology.Comment: 4 pages, 4 figures, 1 table, to be published in J. Phys. Soc. Jpn,
Vol. 79, No. 1
Principle of work of the vortex heat generator installation
Представленная статья содержит краткий анализ вихревых теплогенерирующих установок (ВТУ), обзор актуальности темы исследования, патентноинформационное обоснование, а также проанализированы современные научнообоснованные факты и результаты, как теоретических, так и экспериментальных работ. Исследованы основные основополагающие (физико-химические, технологические процессы, технико-экономические и законодательные обоснования), а также и другие актуальные вопросы касательно ВТУ. The presented article contains a brief analysis of vortex heat-generating plants, an overview of the relevance of the research topic, patent information justification, and also analyzes modern scientifically-based facts and results of both theoretical and experimental work. The basic fundamental (physicochemical, technological processes, feasibility and legislative justifications), as well as other relevant issues regarding vortex heat-generating installations are investigated
Electronic properties of LaOFFeAs in the normal state probed by NMR/NQR
We report 139La, 57Fe and 75As nuclear magnetic resonance (NMR) and nuclear
quadrupole resonance (NQR) measurements on powders of the new LaO1-xFxFeAs
superconductor for x = 0 and x = 0.1 at temperatures up to 480 K, and compare
our measured NQR spectra with local density approximation (LDA) calculations.
For all three nuclei in the x = 0.1 material, it is found that the local Knight
shift increases monotonically with an increase in temperature, and scales with
the macroscopic susceptibility, suggesting a single magnetic degree of freedom.
Surprisingly, the spin lattice relaxation rates for all nuclei also scale with
one another, despite the fact that the form factors for each site sample
different regions of q-space. This result suggests a lack of any q-space
structure in the dynamical spin susceptibility that might be expected in the
presence of antiferromagnetic correlations. Rather, our results are more
compatible with simple quasi-particle scattering. Furthermore, we find that the
increase in the electric field gradient at the As cannot be accounted for by
LDA calculations, suggesting that structural changes, in particular the
position of the As in the unit cell, dominate the NQR response.Comment: 17 pages, 6 figure
AFe2As2 (A = Ca, Sr, Ba, Eu) and SrFe_(2-x)TM_(x)As2 (TM = Mn, Co, Ni): crystal structure, charge doping, magnetism and superconductivity
The electronic structure and physical properties of the pnictide compound
families OFeAs ( = La, Ce, Pr, Nd, Sm), FeAs ( = Ca,
Sr, Ba, Eu), LiFeAs and FeSe are quite similar. Here, we focus on the members
of the FeAs family whose sample composition, quality and single
crystal growth are better controllable compared to the other systems. Using
first principles band structure calculations we focus on understanding the
relationship between the crystal structure, charge doping and magnetism in
FeAs systems. We will elaborate on the tetragonal to
orthorhombic structural distortion along with the associated magnetic order and
anisotropy, influence of doping on the site as well as on the Fe site, and
the changes in the electronic structure as a function of pressure.
Experimentally, we investigate the substitution of Fe in
SrFeAs by other 3 transition metals, = Mn, Co, Ni.
In contrast to a partial substitution of Fe by Co or Ni (electron doping) a
corresponding Mn partial substitution does not lead to the supression of the
antiferromagnetic order or the appearance of superconductivity. Most calculated
properties agree well with the measured properties, but several of them are
sensitive to the As position. For a microscopic understanding of the
electronic structure of this new family of superconductors this structural
feature related to the Fe-As interplay is crucial, but its correct ab initio
treatment still remains an open question.Comment: 27 pages, single colum
Cold atoms in space: community workshop summary and proposed road-map
We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies