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Structural and magnetic characteristics of La0.7Sr0.3Mn0.9Fe0.05Zn0.05O3 + γ and La0.7Sr0.3Mn0.9Fe0.05Mg0.05O3 + γ manganites, in which the iron is Mössbauer isotope 57Fe, are investigated and compared. Ceramic samples were sintered in air at 1473 K. They were then exposed to heat treatments at 1223 K and various partial pressure of oxygen in the gas phase, which ensured the production of manganites with following values of non-stoichiometry index: γ = −0.005; 0; 0.007; 0.008 for Zn-containing manganites (ZnM), and γ = −0.022; 0; 0.002; 0.005 for Mg-containing manganites (MgM). All synthesized manganites have rhombohedral crystal structure. Mössbauer spectroscopy data correspond to Fe3+ (3d5) ions. Curie point and magnetization depend on γ nonmonotonically. ZnM have essentially higher values of magnetic parameters and narrowest temperature interval of "ferromagnetic–paramagnetic" transition as compared with MgM. Their structure is considered as more homogeneous, which corresponds to lower value of quadrupole splitting of Mössbauer spectra. The results obtained indicate that different effect of Zn2+ and Mg2+ ions on electromagnetic characteristics of manganites is mainly determined by the configuration of their electron shells (3d10 and 2p6, correspondingly). [ABSTRACT FROM AUTHOR]

Sub-Doppler, saturation dip, spectra of lines in the v1 + v3, v1 + 2v4, and v3 + 2v4 bands of 14NH3 have been measured by frequency comb-referenced diode laser absorption spectroscopy. The observed spectral line widths are dominated by transit time broadening and show resolved or partially-resolved hyperfine splittings that are primarily determined by the 14N quadrupole coupling. Modeling of the observed line shapes based on the known hyperfine level structure of the ground state of the molecule shows that, in nearly all cases, the excited state level has hyperfine splittings similar to the same rotational level in the ground state. The data provide accurate frequencies for the line positions and easily separate lines overlapped in Doppler-limited spectra. The observed hyperfine splittings can be used to make and confirm rotational assignments and ground state combination differences obtained from the measured frequencies are comparable in accuracy to those obtained from conventional microwave spectroscopy. Several of the measured transitions do not show the quadrupole hyperfine splittings expected based on their existing rotational assignments. Either the assignments are incorrect or the upper levels involved are perturbed in a way that affects the nuclear hyperfine structure. [ABSTRACT FROM AUTHOR]

Sub-Doppler, saturation dip, spectra of lines in the v1 + v3, v1 + 2v4, and v3 + 2v4 bands of 14NH3 have been measured by frequency comb-referenced diode laser absorption spectroscopy. The observed spectral line widths are dominated by transit time broadening and show resolved or partially-resolved hyperfine splittings that are primarily determined by the 14N quadrupole coupling. Modeling of the observed line shapes based on the known hyperfine level structure of the ground state of the molecule shows that, in nearly all cases, the excited state level has hyperfine splittings similar to the same rotational level in the ground state. The data provide accurate frequencies for the line positions and easily separate lines overlapped in Doppler-limited spectra. The observed hyperfine splittings can be used to make and confirm rotational assignments and ground state combination differences obtained from the measured frequencies are comparable in accuracy to those obtained from conventional microwave spectroscopy. Several of the measured transitions do not show the quadrupole hyperfine splittings expected based on their existing rotational assignments. Either the assignments are incorrect or the upper levels involved are perturbed in a way that affects the nuclear hyperfine structure. [ABSTRACT FROM AUTHOR]

We employ a combination of pseudopotential and all-electron density functional calculations, to relate the structure of defects in supercells to the isomer shifts and quadrupole splittings observed in Mössbauer spectroscopy experiments. The methodology is comprehensively reviewed and applied to the technologically relevant case of iron-related defects in silicon, and to other group-IV hosts to a lesser degree. Investigated defects include interstitial and substitutional iron, iron-boron pairs, iron-vacancy, and iron-divacancy. We find that, in general, agreement between the calculations and Mössbauer data is within a 10% error bar. Nonetheless, we show that the methodology can be used to make accurate assignments, including to separate peaks of similar defects in slightly different environments. [ABSTRACT FROM AUTHOR]

Mössbauer spectroscopy is one of the very sensitive tools to study the hyperfine interactions in alloys and compounds. The interaction of the probe with the local environment gives information like spin state, coordination number, magnetic and quadrupole interaction etc. In the present study, 57Fe Mössbauer spectroscopy was used to study the hyperfine interaction of the FexSb1-x-ySey bulk alloy with very dilute quantity of Fe, x = 0.002. The measurements were done at room temperature. Keeping the amount of Fe constant in the bulk alloy at x = 0.002, the concentration of Se was varied from y = 0.000, 0.004, 0.016 to 0.048. Additionally, to see the effect of extremely low concentration of Fe in Sb matrix alone, a sample with Fe concentration of 0.0015 was prepared without any Se substitution in Sb. The structural study was done using X-ray diffraction technique. Neutron depolarization study was done to see if clusters of Fe were present in the samples. The XRD spectra showed Sb peaks with no other compound phases. From Mössbauer spectroscopy, at y = 0.000, x = 0.002 one magnetic site (site A) with hyperfine magnetic field of ~312 kOe was observed. When the concentration of Fe was further reduced to x = 0.0015, there was no change in the hyperfine magnetic field of ~312 kOe. On introduction of Se into the system, we observed two magnetic sites (A and B). The value of hyperfine magnetic field (HMF) for both the sites (A and B) decreases with increases in Se concentration. At higher concentration of Se (y = 0.048) an additional nonmagnetic site (site C) with quadrupole splitting of 0.51 mm/s was also observed. [ABSTRACT FROM AUTHOR]

Ternary intermetallic R5Fe6Sn18 (R = Tm, Lu) compounds have been synthesized from the elements by arc melting, annealed at 670 K and characterized by X-ray powder diffraction and energy dispersive X-ray analyses. Performed structure refinements have shown that they crystallize in the cubic Tb5Rh6Sn18 structure type (space group Fm-3m, a = 13:55399(4) Å, a = 133.53243(5) Å for Tm and Lu compounds, respectively). Using 57Fe Mössbauer spectroscopy it has been found that the magnetic state of the Fe atoms in the Tm5Fe6Sn18 and Lu5Fe6Sn18 stannides is paramagnetic. The value of the isomer shifts for Lu5Fe6Sn18 and Tm5Fe6Sn18 is positive relative to pure Fe. The 57Fe Mössbauer spectra for Lu5Fe6Sn18 and Tm5Fe6Sn18 stannides have shown that the quadrupole splitting for the Fe position (24e) have magnitudes of 0.43 and 0.45 mm/s, respectively. The similarity of these values is consistent with a qualitative crystal structure analysis. The examined Tm5Fe6Sn18 and Lu5Fe6Sn18 compounds have been found to be characterized by metallic-like conductivity and high values of electrical resistivity (672.9 μΩ cm, 623.8 μΩ cm at 300 K for Tm and Lu, respectively). [ABSTRACT FROM AUTHOR]

We report on the crystallographic and magnetic properties of LixFe1/3Mn1/3Ni1/3PO4 (x = 0, 1) using x-ray diffraction (XRD), a vibrating sample magne-tometer (VSM), and Mössbauer spectroscopy. XRD analysis confirmed that the samples have an orthorhombic structure with space group Pnma. From the VSM measurements the samples exhibited an antiferromagnetic behavior with a Curie-Weiss temperature θ = − 162 K for x = 1, and θ = − 303 K for x = 0. The Néel temperature (TN) and spin reorientation temperature (TS) were determined to be 40 K and 10 K for x = 1, and 66 K and 25 K for x = 0. The hyperfine field (Hhf) of LiFe1/3Mn1/3Ni1/3PO4 had smaller values than that of Fe1/3Mn1/3Ni1/3PO4 due to the magnitude of the nearest-neighbor superexchange interaction. Isomer shift (δ) values indicate that the charge states of LiFe1/3Mn1/3Ni1/3PO4 are ferrous (Fe2+), and that of Fe1/3Mn1/3Ni1/3PO4 are ferric (Fe3+). The larger values of the electric quadrupole splitting (δEQ) for the Fe2+ phase compared to the Fe3+ phased originated from the different lattice and valence electron contributions due to the crystalline field and valence transition. Debye temperatures (θD) of 338 ± 5 K (x = 1), and 370 ± 5 K (x = 0) were obtained for the samples. [ABSTRACT FROM AUTHOR]

We developed a computational method for estimating magnetic dipole energy of slab materials using spin density obtained through a density functional approach. The new method can accurately estimate magnetic anisotropy energy (MAE) for slabs from magnetic dipole interaction called shape MAE (SMAE). We investigated ferromagnetic and antiferromagnetic slabs and found that a quadrupole component of atomic spin density suppresses SMAE in ferromagnetic slabs with Fe/MgO interface. In antiferromagnetic MnPt slabs, which have a perpendicular favor originating from the crystalline magnetic dipole interaction, a surface effect at the Mn edge appears as an enhancement of SMAE. [ABSTRACT FROM AUTHOR]

Abstract Iron is the most abundant transition metal in the Earth's interior, yet considerable uncertainties remain as to why mantle-derived rocks have diverse iron isotopic compositions. In particular, the isotopic fractionation behavior of iron in the lower-mantle minerals bridgmanite and ferropericlase are largely unexplored. The reason is that it is challenging to study isotopic fractionation at the high pressures relevant to the deep mantle. Here we report in situ measurements of the mean force constants of iron bonds in these minerals pressurized in diamond anvil cells using the technique of nuclear resonant inelastic X-ray scattering (NRIXS). We find that the transition from high- to low-spin iron in ferropericlase ((Mg 0.75 Fe 0.25)O) at approximately 60 GPa drastically stiffens its iron bonds in the low-spin state. The mean force constant of iron bonds in both Fe-bearing and (Fe,Al)-bearing bridgmanite exhibits softening by 21% at approximately 40–60 GPa, which seems to be associated with changes in the iron local environment during the transition from low to high quadrupole splitting states. These results indicate that in the lower mantle, low-spin ferropericlase is enriched in heavy iron isotopes relative to bridgmanite and metallic iron by +0.15‰ and +0.12‰, respectively. Based on these results, we investigate whether terrestrial magma ocean crystallization could have fractionated iron isotopes. We conclude that this process cannot be responsible for the heavy iron isotope enrichment measured in terrestrial basalts. Highlights • Iron isotope fractionation factors in lower mantle minerals were determined. • Spin states and local site influence the high pressure iron isotopic fractionation. • Limited iron isotope fractionation between minerals and melts is found. • The magma ocean crystallization did not cause terrestrial iron isotopic variations. [ABSTRACT FROM AUTHOR]

Abstract Self-conjugate nuclei in the A ≈ 70 – 80 region have attracted a great deal of attention due to phenomena such as shape coexistence and increasing collectivity along the N = Z line. We investigate the structure of nuclei in this region through lifetime measurements using the GRETINA array. The first implementation of the Differential Recoil Distance Doppler Shift technique with fast radioactive beams is demonstrated and verified through a measurement of the well-known B (E 2 ; 2 1 + → 0 1 +) transition strength in 74Kr. The method is then applied to determine the B (E 2 ; 2 1 + → 0 1 +) transition strength in 74Rb, the heaviest odd–odd N = Z nucleus for which this quantity has been determined. This result and extended systematics along N = Z suggest the dominance of the isoscalar part of the quadrupole transition strengths in self-conjugate nuclei, as well as the possible presence of shape coexistence in 74Rb. [ABSTRACT FROM AUTHOR]

NMR experiments on two kinds of Ce-based superconductors with noncentrosymmetry in the crystal structures were performed. They are CePt3Si and CeIr0.65Co0.35Si3 with 0.75 and 0.55 K of Tc's, respectively. By annealing of the crushed sample, CePt3Si recovers two distinct phases, which are coexistent in the crystal, and one of two phases gets the improved characters of single crystal. The angular dependence of an aligned axis and an applied magnetic field exhibits that the internal field must be parallel to the c-axis at Si site below TN, which appears to be inconsistent with the results obtained by the neutron diffraction. On the other hand, a CeIr0.65Co0.35Si3 sample with noncentrosymmetry also shows a clear Meissner diamagnetization at 0.55 K under an ambient pressure and yields a clear Co NMR spectrum with an electric quadrupole splitting. [ABSTRACT FROM AUTHOR]

Integrability in the Painlevé sense of the trapped ionic system in the quadrupole field with superpositions of rotationally symmetric hexapole and octopole fields is studied. Five integrable cases of the system are reported. First Integrals of the planar motion are founded. Confirming three-dimensional integrability of the equations of motion, the third explicit integrals of motion are constructed directly for each case. We carried out a numerical study to observe the regularity and chaotic regions via the Poincaré surface of sections, and corroborate the analytical results. [ABSTRACT FROM AUTHOR]

Forty-three metabolites including several methoxylated flavonoids, tremetones, and ent-clerodane diterpenes were accurately identified for the first time in the ethanolic extract of P. quadrangularis by means of hyphenated UHPLC-quadrupole Orbitrap mass spectrometry, and seven isolated compounds were tested regarding gastroprotective activity using the HCl/EtOH-induced lesion model in mice. A new tremetone (compound 6) is reported based on spectroscopic evidence. The isolated clerodanes and tremetones showed gastroprotective activity in a mouse model, evidenced by compound 7 (p-coumaroyloxytremetone), which showed the highest gastroprotective activity (76%), which was higher than the control drug lansoprazole (72%). Our findings revealed that several constituents of this plant have gastroprotective activity, and particularly, p-coumaroyloxytremetone could be considered as a lead molecule to explore new gastroprotective agents. This plant is a rich source of biologically active tremetones and terpenoids which can support the ethnobotanical use of the plant. [ABSTRACT FROM AUTHOR]

We developed a new type of dc-to-pulse converter, called FRAC (Fringing-RF-field-Activated dc-to-pulse Converter) for low-energy ion beams electrostatically accelerated from an ion source. FRAC is based on a radio-frequency quadrupole (RFQ) linear trap technique and works in principle under ultrahigh vacuum conditions. Ions continuously injected into FRAC are decelerated by an alternating longitudinal electric field produced in a distorted radio frequency field around the edge region of RFQ rods. These ions accumulate in FRAC for a significantly long time. This edge effect appears most notably when the energy of incoming ions exceeds the injection barrier potential by less than a few eV and the energy spread is quite small. The ions stacked during the FRAC operation period are ejected as a high intensity pulsed beam. We investigated the performance of FRAC and the capability of some FRAC operation methods developed to enhance the dc-to-pulse conversion efficiency. The maximum conversion efficiencies achieved were 22% and 5.6% at FRAC operation frequencies of 10 and 1 Hz, respectively. The number of ions contained in an output beam pulse with a duration of 500 μs was in practice 1.6 × 109 ions/pulse at an injected dc beam intensity of 4.6 nA and an operation frequency of 1 Hz. [ABSTRACT FROM AUTHOR]

Abstract: Four monoferrocenyl tritylium derivatives with donor‐substituted (OMe, NMe2) aryl rings are reported, along with their spectroscopic and electrochemical properties. All the complexes show a one‐electron reduction and a quasi‐reversible ferrocene oxidation at a very positive potential. Small quadrupole splittings, ΔEQ, in Mößbauer spectra agree with highly electron‐deficient ferrocenes. Comparison of the experimental half‐wave potentials for ferrocene oxidation, E1/2 (Fc/Fc+), with those estimated from established correlations of E1/2 (Fc/Fc+) with ΔEQ indicates that the E1/2 values of the anisyl‐substituted congeners FcOMe+ and FcMeOMe+ are affected by Coulombic repulsion between the positive charges at the Fe ion and the neighboring methylium site. Electronic spectra are recorded and interpreted with the aid of quantum chemical calculations. UV/Vis spectroelectrochemical measurements as well as chemical reduction provide insight into the redox‐induced color changes upon ferrocene oxidation or upon reduction to the neutral trityl radicals. The neutral radicals reversibly form EPR‐silent dimers. This process is studied by temperature‐dependent EPR spectroscopy, and thermodynamic data for their dimerization are determined. Experimental and quantum chemical data suggest that the dimers assume classical hexaarylethane structures as opposed to normal or “offset” Jacobson–Nauta‐type structures. [ABSTRACT FROM AUTHOR]

Crystal and magnetic structure of the doped BaFe 12−x In x O 19 samples were refined by the results of investigations using high resolution neutron powder diffraction and vibration sample magnetometry at different temperatures. The refinements were realized in frame of two space groups. The P6 3 /mmc (No 194) centrosymmetric nonpolar and P6 3 mc (No 186) noncentrosymmetric polar space groups were used. The unit cell parameters, ionic coordinates, thermal isotropic factors, occupation positions, bond lengths and bond angles, microstrain values were established. The magnetic and dipole moments were also defined. It is established that the In 3+ cations may be located only in the Fe1 – 2a and Fe2 – 2b crystallographic positions with equal probability for the sample with lowest substitution level x = 0.1. At the x = 1.2 substitution level about half of the In 3+ cations occupies the Fe5 – 12 k positions. For the last sample the remaining half of the In 3+ cations is equiprobably located in the Fe1 – 2a and Fe2 – 2b positions. The spontaneous polarization was established for these compositions at 300 K. It is studied the influence of the type of substitutive cation and structural parameters on the Fe 3+ (i) – O 2− – Fe 3+ (j) (i, j = 1, 2, 3, 4, 5) indirect superexchange interactions with temperature. With substitution level increase the superexchange interactions between the magnetic positions inside and outside the sublattices are broken which leads to a decrease in the value of their magnetic moments. [ABSTRACT FROM AUTHOR]

The structure of ceramic BiFe1‒xZnxO3 multiferroic samples is investigated using the X-ray diffraction method and Mössbauer spectroscopy. X-ray diffraction analysis of the samples indicates the existence of the Bi12(Bi0.5Fe0.5)O19.5 impurity phase. High-temperature heating of the samples generates additional phases. The parameters of the Mössbauer spectra depend on the zinc concentration. In this case, for pure bismuth ferrite, the spectrum is a superposition between two Zeeman sextets and two paramagnetic doublets arising from two nonequivalent magnetic and electrical positions occupied by iron ions at the crystallattice sites of a sample. The replacement of iron ions with zinc ions substantially affects the spectrum parameters. This is probably related to changes in the spin-cycloid structure typical of multiferroics, the destruction of which stimulates the appearance of significant magnetoelectric interactions. [ABSTRACT FROM AUTHOR]

We propose a schematic model of nucleons moving in spin–orbit partner levels, j = l ± 1 2 , to explain Gamow–Teller and two-nucleon transfer data in N = Z nuclei above 40 Ca. Use of the LS coupling scheme provides a more transparent approach to interpret the structure and reaction data. We apply the model to the analysis of charge-exchange, 42 Ca( 3 He,t) 42 Sc, and np-transfer, 40 Ca( 3 He,p) 42 Sc, reactions data to define the elementary modes of excitation in terms of both isovector and isoscalar pairs, whose properties can be determined by adjusting the parameters of the model (spin–orbit splitting, isovector pairing strength and quadrupole matrix element) to the available data. The overall agreement with experiment suggests that the approach captures the main physics ingredients and provides the basis for a boson approximation that can be extended to heavier nuclei. Our analysis also reveals that the SU(4)-symmetry limit is not realized in 42 Sc. [ABSTRACT FROM AUTHOR]

Abstract: The iron(IV) oxido complex [(tmc)Fe=O(OTf)]OTf with the macrocyclic ligand 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclo‐tetradecane (tmc) has been synthesized using ozone as an oxidant. By adding water to this compound the complex [(H2O)(tmc)Fe=O)](OTf)2 could be prepared. This complex is important in regard to a better understanding of the reactivity of FeIV oxido complexes. Mössbauer measurements using the solid compound showed an isomer shift of δ=0.19 mm s−1 and a quadrupole splitting ΔEQ=1.38 mm s−1, confirming the high‐valent FeIV state. DFT calculations were performed and led to an assignment of triplet spin multiplicity. Crystallographic characterization of [(H2O)(tmc)Fe=O)](OTf)2 as well as of starting materials [(tmc)Fe(CH3CN)](OTf)2 and [(tmc)Fe(OTf)]OTf together with previous results strongly suggest that [(H2O)(tmc)Fe=O)](OTf)2 was formed similar to the oxido–hydroxido tautomerism analogous to heme systems. [ABSTRACT FROM AUTHOR]

Mössbauer parameters in a magnetoplumbite-type hexagonal ferrite, SrFe 12 O 19 , are computed using the all-electron band structure calculation based on the density functional theory. The theoretical isomer shift and quadrupole splitting are consistent with experimentally obtained values. The absolute values of hyperfine splitting parameters are found to be underestimated, but the relative scale can be reproduced. The present results validate the site-dependence of Mössbauer parameters obtained by analyzing experimental spectra of hexagonal ferrites. The results also show the usefulness of theoretical calculations for increasing the reliability of interpretation of the Mössbauer spectra. [ABSTRACT FROM AUTHOR]

A vauxite mineral sample from Huanuni, Bolivia, was studied by XRD, TGA and Mössbauer spectroscopy. The XRD revealed the sample as having the typical triclinic structure of vauxite. The chemical formula was determined as (Fe0.88Mn0.01)Al1.99(PO4)2(OH)1.75(H2O)5.31, implying some Fe2+, OH− and H2O deficiencies. The TGA curve showed ca. 27% loss of weight over a temperature range from 80 to 400 °C, supposedly due to the loss of water and hydroxyl groups. For the first time, Mössbauer spectra for vauxite were collected over a wide temperature range between 9 and 310 K. No magnetic ordering was detected. The spectra could be successfully and consistently analyzed by a superposition of four doublet subspectra. On the basis of the relation between the center shift and the mean Fe-ligand distance on the one hand and the center shift values for the various doublets on the other hand, one doublet was assigned to Fe(2). For the other doublets, it is proposed that, as a result of the H2O deficiency in the structure of the present vauxite sample, vacancies are present in the second coordination spheres of some Fe(1) and that these vacancies affect the quadrupole splitting of the corresponding Fe(1) cations, thus causing three Fe(1) doublet components in the Mössbauer spectra. The temperature variations of center shift and quadrupole splitting of the various doublet contributions are presented and discussed. [ABSTRACT FROM AUTHOR]