Search

During the last decade of high-pressure research a whole new series of iron oxides was discovered, like Fe$_4$O$_5$, Fe$_5$O$_6$, Fe$_7$O$_9$ etc., featuring closely related structures with arrays of one-dimensional (1D) chains of trigonal prisms embedded between slabs of octahedra. Here, we develop a unified approach to the series based on a specific crystallographic generation mechanism which predicts the structures of these oxides and naturally classifies them in terms of the slab cycle. When including magnetic interactions, we show that the 1D chains have a symmetry protection against magnetic perturbations from the iron ions in the slabs, and that the slab size determines the type of magnetic order, which is either ferromagnetic or antiferromagnetic. Dynamical mean-field theory calculations reveal the orbitally selective Mott state of the Fe ions and tendency of conductivity to low-dimensional behavior with particular enhancement along the 1D chains. Across the series, the decoupling of the chains increases, and so with the inherent charge ordering of the slabs, these structures have the potential to allow experimental realization of the model system of coupled 1D wires. We point out the possibility to stabilize these compounds in the thin-film form that, together with a wide range of possible ionic substitutions and fact that these compounds are recoverable at ambient pressure, makes them a very promising platform to engineer physical systems with interesting magnetotransport phenomena, as corroborated by the recent discovery of quantum Hall effect in ZrTe$_5$.

The spatial confinement of atoms at surfaces and interfaces significantly alters the lattice dynamics of thin films, heterostructures and multilayers. Ultrathin films with high dielectric constants (high-k) are of paramount interest for applications as gate layers in current and future integrated circuits. Here we report a lattice dynamics study of high-k Eu$_{2}$O$_{3}$ films with thicknesses of 21.3, 2.2, 1.3, and 0.8 nm deposited on YSZ(001). The Eu-partial phonon density of states (PDOS), obtained from nuclear inelastic scattering, exhibits broadening of the phonon peaks accompanied by up to a four-fold enhancement of the number of low-energy states compared to the ab initio calculated PDOS of a perfect Eu$_{2}$O$_{3}$ crystal. Our analysis demonstrates that while the former effect reflects the reduced phonon lifetimes observed in thin films due to scattering from lattice defects, the latter phenomenon arises from an ultrathin EuO layer formed between the thin Eu$_{2}$O$_{3}$ film and the YSZ(001) substrate. Thus, our work uncovers another potential source of vibrational anomalies in thin films and multilayers, which has to be cautiously considered.

Iron oxides are important materials for Geoscience but also for basic science and applied technologies (Kupenko et al., 2019). Iron monoxide is likely to be the final constituent of the evolution of subducted banded iron formations and might be a source of the low-velocity zones at the Earth’s core-mantle boundary (Dobson and Brodholt, 2005). The stability and high-pressure properties of FexO could, thus, determine the fate of banded iron formations and their potential role in processes in Earth and planetary interiors, including controls on redox cycles. FexO has the NaCl (B1) structure at ambient pressure and temperature and transforms into rhombohedral distorted-B1 phase (rB1) at about 16 GPa. A further transition from a rhombohedral rB1 phase to a hexagonal B8 phase has been proposed at 74 GPa and 900 K (Fei and Mao, 1994). Although numerous studies were focused on the investigation of the electronic and magnetic properties and phase diagram of FexO, information on the Fe2+/Fe3+ interplay, magnetic and structural coupling of FexO at high pressures and high temperature are very limited. We will present our investigation on the pressure dependence of the electronic, magnetic and structural properties of FexO by means of Synchrotron Mössbauer Source spectroscopy and Single-Crystal X-ray diffraction with diamond anvil cells up to 94 GPa and 1200 K. We will discuss the interplay between Fe2+ and Fe3+ and its effects on the electronic and magnetic properties of FexO and their potential role in the mineralogy, chemistry, and physics of the Earth’s deep interior.

Nature Communications 13(1), 7517 (2022). doi:10.1038/s41467-022-35110-x, Ferropericlase-magnesiowüstite (Mg,Fe)O is the second most abundant mineral in Earth’s lower mantle and the most common inclusion found in lower mantle diamonds. In pyrolitic mantle, it should theoretically contain < 20 mol% FeO. However, where the mineral is found as inclusions in diamond it shows a broad range of Mg# (Mg/(Mg+Fe)) between 12 and 93. Here we use synchrotron Mössbauer source spectroscopy (SMS), complemented by single-crystal X-ray diffraction to determine the structure and iron oxidation state of two magnesiowüstite and three ferropericlase inclusions in diamonds from São Luiz, Brazil. The Mg# of these inclusions varies between 16.1 and 84.5. All three ferropericlase inclusions are monomineralic and contain no ferric iron within the detection limit of SMS. Both magnesiowüstite inclusions show the presence of monocrystalline magnesioferrite (Mg,Fe)Fe$^{3+}$$_2$O$_4$) with an estimated 47-53 wt% of Fe$_2$O$_3$. We argue that the wide range of Fe concentrations observed in (Mg,Fe)O inclusions in diamonds and the appearance of magnesioferrite in Fe-rich inclusions result from oxidation of ferropericlase triggered by the introduction of subducted material into the lower mantle. Subducted carbonates react with Fe-metal to generate diamond and magnesiowüstite. Upon local metal exhaustion, the reaction continues with oxidation of magnesiowüstite into magnesioferrite, forming highly oxidised areas in the lower mantle., Published by Nature Publishing Group UK, [London]

В работе представлены актуальные проблемы современного менеджмента в России и даны рекомендации по повышению производительности труда, а также возвращению менеджменту важной роли в развитии экономики и увеличению благосостояния граждан.

We report on the depth dependence and technological limits of the phase transition of the iron rhodium alloy as function of temperature, external magnetic and electric fields in the FeRh/BaTiO3 multiferroic, determined by grazing-incidence nuclear resonant scattering measurements. The change of temperature induces a continuous and homogenous antiferromagnetic / ferromagnetic phase transition through the entire FeRh layer, except in the near substrate region. External magnetic field does not affect this mechanism, but the application of electric field changes it fundamentally (via piezoelectric strain): the phase transition of the alloy suddenly propagates from the substrate up to a height, defined by the combination of temperature and external magnetic field, as soon as the applied electric field reaches ~ 20 kV/m., Comment: 22 pages, 12 figures

We report the results of a search for a light pseudoscalar particle a that couples to electrons and decays to e+e− performed using the high-energy CERN SPS H4 electron beam. If such light pseudoscalar exists, it could explain the ATOMKI anomaly (an excess of e+e− pairs in the nuclear transitions of 8Be and 4He nuclei at the invariant mass ≃17 MeV observed by the experiment at the 5 MV Van de Graaff accelerator at ATOMKI, Hungary). We used the NA64 data collected in the “visible mode” configuration with a total statistics corresponding to 8.4×1010 electrons on target (EOT) in 2017 and 2018. In order to increase sensitivity to small coupling parameter ε we also used the data collected in 2016-2018 in the “invisible mode” configuration of NA64 with a total statistics corresponding to 2.84×1011 EOT. The background and efficiency estimates for these two configurations were retained from our previous analyses searching for light vector bosons and axionlike particles (ALP) (the latter were assumed to couple predominantly to γ). In this work we recalculate the signal yields, which are different due to different cross section and lifetime of a pseudoscalar particle a, and perform a new statistical analysis. As a result, the region of the two dimensional parameter space ma−ε in the mass range from 1 to 17.1 MeV is excluded. At the mass of the central value of the ATOMKI anomaly (the first result obtained on the beryllium nucleus, 16.7 MeV) the values of ε in the range 2.1×10−4

The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson A′ were set by the NA64 experiment for the mass region mA′≲250 MeV, by analyzing data from the interaction of 2.84×1011 100-GeV electrons with an active thick target and searching for missing-energy events. In this work, by including A′ production via secondary positron annihilation with atomic electrons, we extend these limits in the 200-300 MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations. Our new results demonstrate the power of the resonant annihilation process in missing energy dark-matter searches, paving the road to future dedicated e+ beam efforts.

Physical review / B 105(5), 054417 (2022). doi:10.1103/PhysRevB.105.054417, Iron(IV) oxides are strongly correlated materials with negative charge-transfer energy (negative $Δ$), and exhibit peculiar electronic and magnetic properties such as topological helical spin structures in the metallic cubic perovskite SrFeO$_3$. Here, the spin structure of the layered negative-$Δ$ insulator Sr$_2$FeO$_4$ was studied by powder neutron diffraction in zero field and magnetic fields up to 6.5 T. Below $T_N$=56K, Sr$_2$FeO$_4$ adopts an elliptical cycloidal spin structure with modulated magnetic moments between 1.9 and 3.5 $μ_B$ and a propagation vector k=($τ,τ$,0) with $τ$=0.137. With increasing magnetic field the spin structure undergoes a spin-flop transition near 5 T. Synchrotron $^{57}$Fe-Mössbauer spectroscopy reveals that the spin spiral transforms to a ferromagnetic structure at pressures between 5 and 8 GPa, just in the pressure range where a Raman-active phonon nonintrinsic to the K$_2$NiF$_4$-type crystal structure vanishes. These results indicate an insulating ground state which is stabilized by a hidden structural distortion and differs from the charge disproportionation in other Fe(IV) oxides., Published by Inst., Woodbury, NY

Nanostructured thin films on a silicon substrate were obtained using a high-frequency pulse-periodic f-10-15 kHz laser action at a wavelength y = 1.064 µm, a power density q = 85 MW/cm 2, and a pressure in a vacuum chamber p = 2*10-2 mm Hg on zinc oxide ceramics doped with scandium oxide. The morphology of the obtained films was studied using atomic force microscopy. Методом высокочастотного импульсно-периодического (f -10-15 кГц) лазерного воздействия с длиной волны y = 1.064 мкм и плотностью мощности q = 85 МВт/см 2 на керамику из оксида цинка, легированную оксидом скандия, при давлении в вакуумной камере p = 2*10-2 мм рт. ст. получены наноструктурированные тонкие пленки на кремниевой подложке. Изучена морфология полученных пленок с помощью атомно-силовой микроскопии.

Physical review / B covering condensed matter and materials physics 101(3), 035112 (2020). doi:10.1103/PhysRevB.101.035112, Published by Inst., Woodbury, NY

Проведены исследования тонких пленок, осажденных в вакууме (2*10-2 мм рт. ст.) на кремниевую и стеклянную подложки при многоимпульсном высокочастотном (10-15 кГц) лазерном воздействии (плотность мощности лазерного излучения 100 МВт/см2 и расстояние от мишени до подложки 40 мм), на керамику из оксида циркония ZrO2, легированную оксидом иттрия 5 % Y2O3. The thin films deposited in vacuum (2*10-2 mm Hg) on the silicon and glass substrates under the multi-pulse high-frequency (10-15 kHz) laser exposure (laser radiation power density 100 MW/cm2 and the distance from the target to the substrate 40 mm) for zirconium oxide ZrO2 ceramics doped with yttrium oxide 5 % Y2O3.

An X-ray free-electron laser oscillator (XFELO) is a new type of hard X-ray source that would produce fully coherent pulses with meV bandwidth and stable intensity. The XFELO complements existing sources based on self-amplified spontaneous emission (SASE) from high-gain X-ray free-electron lasers (XFEL) that produce ultra-short pulses with broad-band chaotic spectra. This report is based on discussions of scientific opportunities enabled by an XFELO during a workshop held at SLAC on June 29 - July 1, 2016, 21 pages, 12 figures

The densities of phonon states of thin Sn films on InSb substrates are determined during different stages of the alpha-Sn to beta-Sn phase transition using nuclear inelastic x-ray scattering. The vibrational entropy and internal energy per atom as a function of temperature are obtained by numerical integration of the phonon density of states. The free energy as a function of temperature for the nanoscale samples is compared to the free energy obtained from ab initio calculations of bulk tin in the alpha-Sn and beta-Sn phase. In thin films this phase transition is governed by the interplay between the vibrational behavior of the film (the phase transition is driven by the vibrational entropy) and the stabilizing influence of the substrate (which depends on the film thickness). This brings a deeper understanding of the role of lattice vibrations in the phase transition of nanoscale Sn.

в статье рассматриваются исторические аспекты корпоративных информационных систем управления в различных сферах деятельности.

We have tested the new experimental techniques in the M\"ossbauer spectroscopy with Synchrotron M\"ossbauer Source by using the polarization analysis of the reflected radiation. In particular we have shown that the dichroic components in M\"ossbauer spectra create the scattering intensity with "rotated" polarization. The angular dependence for such component in the reflected signal is characterized by the peak near the critical angle of the total external reflection, and in the case of the collinear antiferromagnetic interlayer ordering the "magnetic" maxima on the reflectivity curve are formed mainly by this "rotated" polarization. The first experiment on M\"ossbauer reflectivity with selection of the "rotated" polarization shows the expected peak near the critical angle. The measured M\"ossbauer reflectivity spectra of the "rotated" polarization near the critical angle are rather different from the M\"ossbauer reflectivity spectra, measured without polarization analysis. They contain a smaller number of lines and can simplify the interpretation of the poorly resolved spectra. The enhanced surface sensitivity of the new technique is discussed., Comment: 17 pages, 8 figures

Valence and spin states of Fe were investigated in a glass of almandine (Fe3Al2Si3O12) composition to 91 GPa by X ray emission spectroscopy and energy and time domain synchrotron Mössbauer spectroscopy in the diamond anvil cell. Changes in optical properties total spin moment and Mössbauer parameters all occur predominantly between 1 bar and 30 GPa. Over this pressure range the glass changes from translucent brown to opaque and black. The total spin moment of the glass derived from X ray emission spectroscopy decreases by 20. The complementary Mössbauer spectroscopy approaches reveal consistent changes in sites corresponding to 80–90 Fe2+ and 10–20 Fe3+. The high spin Fe2+ doublet exhibits a continuous decrease in isomer shift and increase in line width and asymmetry. A high spin Fe3+ doublet with quadrupole splitting of 1.2 mm/s is replaced by a doublet with quadrupole splitting of 1.9 mm/s a value higher than all previous measurements of high spin Fe3+ and consistent with low spin Fe3+. These observations suggest that Fe3+ in the glass undergoes a continual transition from a high spin to a low spin state between 1 bar and 30 GPa. Almandine glass is not expected to undergo any abrupt transitions in electronic state at deep mantle pressures.

We have tested the new experimental techniques in the M��ssbauer spectroscopy with Synchrotron M��ssbauer Source by using the polarization analysis of the reflected radiation. In particular we have shown that the dichroic components in M��ssbauer spectra create the scattering intensity with "rotated" polarization. The angular dependence for such component in the reflected signal is characterized by the peak near the critical angle of the total external reflection, and in the case of the collinear antiferromagnetic interlayer ordering the "magnetic" maxima on the reflectivity curve are formed mainly by this "rotated" polarization. The first experiment on M��ssbauer reflectivity with selection of the "rotated" polarization shows the expected peak near the critical angle. The measured M��ssbauer reflectivity spectra of the "rotated" polarization near the critical angle are rather different from the M��ssbauer reflectivity spectra, measured without polarization analysis. They contain a smaller number of lines and can simplify the interpretation of the poorly resolved spectra. The enhanced surface sensitivity of the new technique is discussed., 17 pages, 8 figures

We have searched for exclusive production of exotic charmonia in the reaction μ+N→μ+(J/ψπ+π−)π±N′ using COMPASS data collected with incoming muons of 160 GeV/c and 200 GeV/c momentum. In the J/ψπ+π− mass distribution we observe a signal with a statistical significance of 4.1 σ. Its mass and width are consistent with those of the X(3872). The shape of the π+π− mass distribution from the observed decay into J/ψπ+π− shows disagreement with previous observations for X(3872). The observed signal may be interpreted as a possible evidence of a new charmonium state. It could be associated with a neutral partner of X(3872) with C=−1 predicted by a tetraquark model. The product of cross section and branching fraction of the decay of the observed state into J/ψπ+π− is determined to be 71±28(stat)±39(syst) pb.

We have performed the most comprehensive resonance-model fit of π−π−π+ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction π−+p→π−π−π++precoil with a 190 GeV/c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5

We present a precise measurement of the proton longitudinal double-spin asymmetry A1p and the proton spin-dependent structure function g1p at photonvirtualities 0.006(GeV/c)2

в данной статье рассмотрены ключевые особенности использования бизнес-симуляторов при подготовке специалистов экономического профиля.

В работе обосновано выделение изучения квалификационного потенциала в структуре трудового и человеческого потенциала на уровне отдельного предприятия как максимально возможной степени овладения профессией на данном предприятии. Авторы сравнивают социологический и экономический подход к определению квалификационного потенциала и делают выбор в пользу последнего. Обосновывается сужение поля исследования до вопросов квалификационного потенциала в сфере торговли, рассмотрены проблемы определения уровня квалификации в торговле и то, как их решают предприниматели отрасли. Приведена собранная авторами статистика по уровням квалификации в торговле. Рассмотрены вопросы определения квалификации и квалификационных уровней в торговле. Предложены дополнительные факторы, влияющие на квалификационный потенциал. Предложены способы оценки квалификации работника в торговле. Сформулированы перспективы и сложности использования тренингов для повышения квалификационного потенциала.

В работе обосновано выделение изучения квалификационного потенциала в структуре трудового и человеческого потенциала на уровне отдельного предприятия как максимально возможной степени овладения профессией на данном предприятии. Авторы сравнивают социологический и экономический подход к определению квалификационного потенциала и делают выбор в пользу последнего. Обосновывается сужение поля исследования до вопросов квалификационного потенциала в сфере торговли, рассмотрены проблемы определения уровня квалификации в торговле и то, как их решают предприниматели отрасли. Приведена собранная авторами статистика по уровням квалификации в торговле. Рассмотрены вопросы определения квалификации и квалификационных уровней в торговле. Предложены дополнительные факторы, влияющие на квалификационный потенциал. Предложены способы оценки квалификации работника в торговле. Сформулированы перспективы и сложности использования тренингов для повышения квалификационного потенциала.

в статье рассматриваются современные подходы предоставления образовательной услуги. Информационно-коммуникационные технологии позволяют сделать обучение предпринимателей более интересным. Автор отмечает, что появляются все новые и новые проекты и изобретения в этой области использования сети

Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O-3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mossbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mossbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10-50% Fe/total cations, 0-25% Al/total cations, 12-100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mossbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at similar to 70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mossbauer sites with center shift similar to 1 mm/s and quadrupole splitting 2.4-3.1 and 3.9 mm/s at similar to 70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to similar to 20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.