132 research outputs found
Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6
The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of
spin structures that differ in the spin sequence of ferrimagnetic iron - osmium
layers along the tetragonal c-axis. Neutron powder diffraction experiments,
57Fe M\"ossbauer spectra, and density-functional theory calculations suggest
that this behavior arises because a lattice instability resulting in
alternating iron-osmium distances fine-tunes the balance of competing exchange
interactions. Thus, Sr2FeOsO6 is an example for a double perovskite, in which
the electronic phases are controlled by the interplay of spin, orbital, and
lattice degrees of freedom.Comment: 8 Pages, 3 Figure
Upper critical field, lower critical field and critical current density of FeTe0.60Se0.40 single crystal
The transport and magnetic studies are performed on high quality
FeTe0.60Se0.40 single crystals to determine the upper critical fields (Hc2),
lower critical field (Hc1) and the Critical current density (Jc). The value of
upper critical field Hc2 are very large, whereas the activation energy as
determined from the slope of the Arrhenius plots are was found to be lower than
that in the FeAs122 superconductor. The lower critical field was determined in
ab direction and c direction of the crystal, and was found to have a anisotropy
of 'gamma'{=(Hc1//c) / (Hc1//b)} ~ 4. The magnetic isotherms measured up to 12
Tesla shows the presence of fishtail behavior. The critical current densities
at 1.8K of the single crystal was found to almost same in both ab and c
direction as 1X105 Amp/cm2 in low field regime.Comment: 9 pages, 6 figure
High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe
We have studied the structural and superconducting properties of tetragonal
FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil
cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller
than the rest of Fe based superconductors. At 12GPa we observe a phase
transition from the tetragonal to an orthorhombic symmetry. The high pressure
orthorhombic phase has a higher Tc reaching 34K at 22GPa.Comment: 15 pages, 4 figure
Physical properties of FeSeTe single crystals grown under different conditions
We report on structural, magnetic, conductivity, and thermodynamic studies of
FeSeTe single crystals grown by self-flux and Bridgman methods.
The samples were prepared from starting materials of different purity at
various temperatures and cooling rates. The lowest values of the susceptibility
in the normal state, the highest transition temperature of 14.5 K, and
the largest heat-capacity anomaly at were obtained for pure (oxygen-free)
samples. The critical current density of A/cm (at 2
K) achieved in pure samples is attributed to intrinsic inhomogeneity due to
disorder at the cation and anion sites. The impure samples show increased
up to A/cm due to additional pinning centers of
FeO. The upper critical field of kOe is estimated
from the resistivity study in magnetic fields parallel to the \emph{c}-axis.
The anisotropy of the upper critical field reaches a value at . Extremely low values of the residual Sommerfeld coefficient for pure
samples indicate a high volume fraction of the superconducting phase (up to
97%). The electronic contribution to the specific heat in the superconducting
state is well described within a single-band BCS model with a temperature
dependent gap K. A broad cusp-like anomaly in the electronic
specific heat of samples with suppressed bulk superconductivity is ascribed to
a splitting of the ground state of the interstitial Fe ions. This
contribution is fully suppressed in the ordered state in samples with bulk
superconductivity.Comment: 11 pages, 11 figures, 3 table
Search for TeV gamma-rays from SN 1987A in 2001
We searched for TeV gamma-rays from the remnant of SN 1987A around 5400 days
after the supernova. The observations were carried out in 2001, from November
16 to December 11, using the CANGAROO-II Imaging Atmospheric Cherenkov
Telescope. In total, 708 minutes of ON- and 1019 minutes of OFF-source data
were obtained under good conditions. The detection threshold was estimated to
be 1 TeV, due to the mean zenith angle of 39. The upper limits for the
gamma-ray flux were obtained and compared with the previous observations and
theoretical models. The observations indicate that the gamma-ray luminosity is
lower than erg s at TeV.Comment: 8 pages, 3 figures, submitted for publication, style file adde
Update on the Combined Analysis of Muon Measurements from Nine Air Shower Experiments
Over the last two decades, various experiments have measured muon densities in extensive air showers over several orders of magnitude in primary energy. While some experiments observed differences in the muon densities between simulated and experimentally measured air showers, others reported no discrepancies. We will present an update of the meta-analysis of muon measurements from nine air shower experiments, covering shower energies between a few PeV and tens of EeV and muon threshold energies from a few 100 MeV to about 10GeV. In order to compare measurements from different experiments, their energy scale was cross-calibrated and the experimental data has been compared using a universal reference scale based on air shower simulations. Above 10 PeV, we find a muon excess with respect to simulations for all hadronic interaction models, which is increasing with shower energy. For EPOS-LHC and QGSJet-II.04 the significance of the slope of the increase is analyzed in detail under different assumptions of the individual experimental uncertainties
Temperature- and Light-Induced Spin Crossover Observed by X-ray Spectroscopy on Isolated Fe(II) Complexes on Gold
Using X-ray absorption techniques, we show that temperature- and light-induced spin crossover properties are conserved for a submonolayer of the [Fe(H2B(pz)2)2(2,2′-bipy)] complex evaporated onto a Au(111) surface. For a significant fraction of the molecules, we see changes in the absorption at the L2,3 edges that are consistent with those observed in bulk and thick film references. Assignment of these changes to spin crossover is further supported by multiplet calculations to simulate the X-ray absorption spectra. As others have observed in experiments on monolayer coverages, we find that many molecules in our submonolayer system remain pinned in one of the two spin states. Our results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur
Как придать импульс развитию российской экономики: приоритеты действий (предложения к Основным направлениям деятельности Правительства РФ до 2024 г.)
This report was prepared by the staff of the Institute for Economic Forecast of the Russian Academy of Sciences and the Financial University under the Government of the Russian Federation. It gives suggestions to implement priority measures to facilitate the transfer the Russian economy to the direction defined by the Decree of the President of the Russian Federation (est. May 7, 2018). The report also highlights priority directions of the economic policy, primarily in investment activity, development of the domestic market, as well as financial and organizational support for the suggested actions.В докладе, подготовленном сотрудниками Института народнохозяйственного прогнозирования РАН и Финансового университета при Правительстве Российской Федерации, представлены предложения по первоочередным мерам, способствующим переводу российской экономики на траекторию, определенную Указом Президента Российской Федерации от 07.05.2018. Выделены приоритетные направления экономической политики, прежде всего, в инвестиционной деятельности, развитии внутреннего рынка, а также финансового и организационного обеспечения предлагаемых мер
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