<Superscript>57</Superscript>Fe Mössbauer study of the chainpur meteorite

The Chainpur meteorite is one of 23 ordinary chondrites classified as LL3-type (low-Fe & low-metal). It was observed as a shower of stones falling on May 9, 1907 in Uttar Pradesh, India. We report here the characterization of the Fe-bearing phases in this chondrite using ⁵⁷Fe Mössbauer spectroscopy carried out at 298 K, 120 K, 50 K and 13 K. The paramagnetic doublets of olivine and pyroxene dominate the room temperature spectrum, accounting for around 70 % of the spectral area. Moreover, a doublet present with a spectral area of 5 % and assigned to a superparamagnetic Fe ³⁺ phase is a consequence of terrestrial weathering. On the basis of the measured ⁵⁷Fe electric quadrupole splitting of the olivine component at room temperature we estimate the mean Fe:Mg ratio in this meteoritic olivine to be around 35:65 % although there is clearly a wide range of composition. The effects of magnetic ordering of the major components olivine and pyroxene are observed at 13 K.     

Mössbauer investigations of the CaMn<Subscript>7</Subscript>O<Subscript>12</Subscript> double manganite with the nuclei of <Superscript>57</Superscript>Fe probe atoms

The CaMn₇O₁₂ double perovskite-like manganite is studied using Mössbauer spectroscopy with ⁵⁷Fe impurity atoms. The hyperfine parameters of the Mössbauer spectra are found to reflect the specific local structure of this oxide. It is found that the phase transition at T ≈ 90 K is associated with the ordering of the magnetic moments of manganese cations in the octahedral sublattice. The structural phase transition R \(\overline 3 \) ? Im \(\overline 3 \) is shown to occur in the temperature interval from 380 to 450 K, where the rhombohedral (R \(\overline 3 \)) and cubic (Im \(\overline 3 \)) phases of the manganite coexist.     

Single-crystalline M-type Sr Hexaferrites studied by <Superscript>57</Superscript>Fe Mössbauer spectroscopy

The ⁵⁷Fe Mössbauer spectra of the single crystalline and the finely ground Sr_1?x La _x Fe_12?y Co _y O₁₉ (x = 0 : y = 0, x = 0.192 : y = 0.152 and x = 0.456 : y = 0.225) samples have been measured to investigate the La-Co substitution effects. All observed spectra at 150 K were well fitted using the five subspectra which correspond to the five crystallographical nonequivalent Fe sites in the M-type hexaferrite, indicating that the valence changes to Fe²⁺ ions in the Fe³⁺ ions were not observed in our Sr_1?x La _x Fe_12?y Co _y O₁₉ samples. In SrFe₁₂O₁₉, the relative absorption intensities in the five subspectra show the large anisotropies in the recoilless fractions at the five Fe sites whereas these anisotropies were not observed in Sr_0.544La_0.456Fe_11.775Co_0.225O₁₉. These results indicate the chemical compositional dependence on the anisotropies of the recoilless fractions at the five Fe sites. The substitution of a Co²⁺ ion for the Fe³⁺ ion changes the center shifts of the Fe³⁺ ions near the Co²⁺ ion by the perturbation of the Fe-O-Co hybridizations. Therefore, the Co²⁺ ions occupy the 4f ₁ and the 4f ₂ sites due to the chemical compositional dependences of the refined magnetic hyperfine field and center shifts of the Fe³⁺ ions.     

Modification of Mössbauer reflection spectra of group AIIBVI single crystals with Fe<Superscript>57</Superscript> nuclei under influence of infrared radiation

Interaction of Mössbauer gamma radiation with ultrasound vibrations in group AIIBVI single crystals of CdS and CdSe with Fe⁵⁷ impurity nuclei under action of infrared radiation is investigated. It is shown that the infrared irradiation excites a phonon field in single crystals. Similar to the case of optical irradiation of single crystals the shape of their Mössbauer spectrum is modified. The effect of double modulation of resonant gamma radiation by infrared radiation has been observed.     

A study of thermodynamic properties of dilute Fe-Ru alloys by <Superscript>57</Superscript>Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for Fe_1?x Ru _x solid solutions with x in the range 0.01 ≤ x ≤ 0.08. The obtained data were analysed in terms of short-range order parameter (SRO) and the binding energy E _b between two ruthenium atoms in the studied materials using the extended Hrynkiewicz-Królas idea. The extrapolated value of E _b for x = 0 was used to compute the enthalpy of solution H _FeRu of Ru in Fe matrix. The result was compared with corresponding values given in the literature which were derived from experimental calorimetric data as well as with the value resulting from the cellular atomic model of alloys by Miedema. It was found that all the H _FeRu values are negative or Ru atoms interact repulsively. At the same time, the Mössbauer data were used to determine values of the short-range order parameter α ₁. For the as-obtained samples in which atoms are frozen-in high temperature state, close to the melting point, the negative α ₁ values were found. The findings indicates ordering tendencies in such specimens. On the other hand, in the case of the annealed samples where the observed distributions of atoms should be frozen-in state corresponding to the temperature 700 K, the Fe_1?x Ru _x alloys with x ≥ 0.05 exhibit clustering tendencies (a predominance of Fe-Fe and Ru-Ru bonds), which manifest themselves by positive values of the calculated SRO parameter. The clustering process leads to a local increase in ruthenium concentration and nucleation of a new ruthenium-rich phase with the hcp structure.     

Sensitivity of <Superscript>57</Superscript>Fe emission Mössbauer spectroscopy to Ar and C induced defects in ZnO

Emission Mössbauer Spectroscopy (eMS) measurements, following low fluence (<10¹² cm^?2) implantation of ⁵⁷Mn (t _1/2 = 1.5 min.) into ZnO single crystals pre-implanted with Ar and C ions, has been utilized to test the sensitivity of the ⁵⁷Fe eMS technique to the different types of defects generated by the different ion species. The dominant feature of the Mössbauer spectrum of the Ar implanted ZnO sample was a magnetic hyperfine field distribution component, attributed to paramagnetic Fe³⁺, while that of the C implanted sample was a doublet attributed to substitutional Fe²⁺ forming a complex with the C dopant ions in the 2^? state at O vacancies. Magnetization measurements on the two samples, on the other hand, yield practically identical m(H) curves. The distinctly different eMS spectra of the two samples display the sensitivity of the probe nucleus to the defects produced by the different ion species.     

Synthetic versiliaite and apuanite: investigation by <Superscript>57</Superscript>Fe Mössbauer spectroscopy

The minerals versiliaite and apuanite have been synthesised for the first time. The ⁵⁷Fe Mössbauer spectra recorded at 298 and 4 K are reported. The results are indicative of a formulation for versiliaite as \(\left (\text {Fe}_{4}^{2+}\text {Fe}_{4}^{3+}\right )^{\text {oct}}\left [\text {Fe}_{4}^{3+}\text {Sb}_{12}^{3+}\right ]^{\text {tet}}\textit {O}_{32}\textit {S}_{2}\) and of apuanite as \(\left (\text {Fe}_{4}^{2+}\text {Fe}_{8}^{3+}\right )^{\text {oct}}\left [\text {Fe}_{8}^{3+}\text {Sb}_{16}^{3+}\right ]^{\text {tet}}\textit {O}_{48}\textit {S}_{\mathrm {4.}}\) The spectra recorded at low temperature are indicative of complex magnetic interactions. The results indicate the potential for the synthesis of further new structurally-related materials with different compositions and new low dimensional physical properties.     

Experimental search for the effect of resonant environment on the Mössbauer absorption of gamma rays by <Superscript>57</Superscript>Fe

Due to the virtual photon exchange between atomic nuclei and the field of zero-point electromagnetic oscillations, some nuclei of a given sample are in a virtual excited state with the lifetime ～?/E, where E is the energy of nuclear level. For ⁵⁷Fe nuclei, whose first excited state has an energy of 14.4 keV, this time is equal to ～4.6×10^?20 s. If a thin ⁵⁷Fe Mössbauer gamma-ray absorber is surrounded by a thick screen of the same atoms, the number of virtual excited nuclei in the absorber decreases and, at first glance, it should more strongly absorb Mössbauer gamma rays emitted by an external source and passing through the absorber. In this work, the ratio of the intensities of 14.4-keV gamma rays emitted by the ⁵⁷Fe nuclide and passing through the thin resonant absorber is measured in the absence and presence of the resonant screen around the absorber. Comparison shows that these ratios measured for the gamma source at rest and in the oscillating state differ by 0.00123±0.00075. This value should be treated as the upper limit for the desired effect under these experimental conditions.     

Influence of laser radiation on the Mössbauer absorption spectra of CdS (Fe<Superscript>57</Superscript>) single crystal

Influence of laser radiation on the resonant absorption of gamma radiation from Fe⁵⁷ nuclei in cadmium sulphide is investigated. It is shown that under action of laser radiation the shape of the Mössbauer spectrum of the sample is modified. The observed modification of the spectrum is explained by the presence in the sample of acoustic vibrations arising as a result of photoacoustic effect.     

<Superscript>57</Superscript>Fe emission Mössbauer spectroscopy following dilute implantation of <Superscript>57</Superscript>Mn into In <Subscript>2</Subscript>O<Subscript>3</Subscript>

Emission Mössbauer spectroscopy has been utilised to characterize dilute ⁵⁷Fe impurities in In ₂O₃ following implantation of ⁵⁷Mn (T _1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In ³⁺, however the spectra are dominated by spectral lines due to paramagnetic Fe²⁺. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe²⁺ state in In ₂O₃. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In ₂O₃. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature.     

An <Emphasis Type="Italic">X</Emphasis><Subscript>α</Subscript>-discrete variation method for calculating the electronic structure and parameters of Mössbauer spectra of <Superscript>57</Superscript>Fe nuclei in iron oxide compounds exhibiting high states of oxidation

An X _α-discrete variation method is ab initio applied to calculate the electronic structure and chemical bonding parameters in [Fe^m+O₄]^{m ? 8} and m = 3+ … 8+ clusters in iron oxide compounds. The tendencies of change in the Mössbauer spectra parameters of iron within these clusters can be accounted for by the formation of two types of Fe3d-AO sub-bands, the occupied hybrid structureless and the vacant basic.     

<Superscript>57</Superscript>Fe Mössbauer,SEM/EDX,p-XRF and μ-XRF studies on a Dutch painting

The painting of a rich Jewish merchant “Bildnis eines jüdischen Kaufmanns” from the Netherlands is dated presumably to the 16^th century. After a vivid historical background, i.e. robbed by the Nazis by order of Hermann Göring, it was recently discovered on an Austrian flea market. Different analysis methods were combined to identify the time of the production of this historically interesting looted art. Non-destructive MIMOS II Fe-57 Mössbauer spectroscopy was utilised for mesurements in selected spots. This mainly revealed haematite (α-Fe₂O₃) in the red curtain. In spots of the brown jacket Mössbauer spectra indicated the presence of mainly Iron(III) in super-paramagnetic oxide or oxide-hydroxide. Consecutively SEM measurements revealed a restoration by partly over-painting. The elementary composition of the pigments was examined by a portable-X-ray fluorescence. μ-XRF analysis for element distribution at different areas was performed. The look into a crack showed Zinc-white at the bottom of the crack. Traces of Titanium-white could be found within some locations on the surface of the painting. In terms of provenance of the artwork, the presence of Zink-white suggests that the painting was painted around the 19^th century. Titanium-white indicates a reconstruction during the 20^th century, approximately between 1917 and 1958.     

Mössbauer effect study of Bi<Subscript>0.8</Subscript>La<Subscript>0.2</Subscript>FeO<Subscript>3</Subscript> multiferroic on <Superscript>57</Superscript>Fe nuclei

The parameters of hyperfine interactions in the Bi_0.8La_0.2FeO₃ multiferroic have been measured by Mössbauer spectroscopy in the temperature range of 87–850 K. It has been found that the spatial spin-modulated structure that exists in BiFeO3 is destroyed in the substitution of La for 0.2 mol % of Bi and the homogeneous antiferromagnetic structure appears. The temperatures of the magnetic (Néel temperature, T _N = 677 ± 3 K) and ferroelectric (Curie temperature, T _C = 773 ± 3 K) transitions and the Debye temperature (Θ = 431 ± 12) have been measured.     

Mössbauer spectroscopy of <Superscript>57</Superscript>Fe in <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> following implantation of <Superscript>57</Superscript>Mn<Superscript>*</Superscript>

Two Fe/MCM-41 systems, one of them sylilated, were obtained to be used as catalysts in Fischer–Tropsch reaction. They have more than 90% of the iron species located inside the support channels, leading to a narrow crystal size distribution accessible to reactive gases. The samples were characterized by X-ray diffraction, atomic absorption spectroscopy, N₂ adsorption, Mössbauer spectroscopy and Fourier transformer infrared spectroscopy. Mössbauer spectroscopy allowed us to demonstrate that the catalytic active species were the same in both catalysts. The only difference between them was the surface hydrophobicity, which decreases the “water gas shift reaction” in the sylilated catalyst. Besides, this solid is more active for hydrocarbon production, with a lower methane yield.     

Search for resonant absorption of solar axions emitted in M1 transition in <Superscript>57</Superscript>Fe nuclei

A search for resonant absorption of 14.4 keV solar axions by a ⁵⁷Fe target was performed. The Si(Li) detector placed inside the low-background setup was used to detect the γ-quanta appearing in the deexcitation of the 14.4 keV nuclear level: A+⁵⁷Fe→⁵⁷Fe^*→⁵⁷Fe+γ. The new upper limit for the hadronic axion mass has been obtained of m _A ≤159 eV (95% c.l.) (S=0.5, z=0.56).     

Mössbauer study of SnO<Subscript>2</Subscript> powders doped with dilute <Superscript>57</Superscript>Fe prepared by a sol-gel method

SnO₂ powders, doped with various ⁵⁷Fe contents were prepared by a sol-gel method, and annealed finally at 500 °C and 650 °C. These samples were characterized by Mössbauer spectroscopy, vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) to investigate the relationship of magnetic properties, grain sizes, annealing temperatures and Mössbauer parameters. The particle sizes of SnO₂ powders reduced to less than 100 nm with the increase of Fe contents up to 5%. Rutile SnO₂ was the only phase obtained for all samples. Room temperature Mössbauer spectra suggest the presence of two different paramagnetic iron sites for all samples and one magnetically relaxed species for those samples with the lowest iron concentrations. The magnetization increased with the Fe content, but was reduced for the samples annealed at 650 °C perhaps due to a segregation of α-Fe₂O₃ doped with tin.     

The method of invariants applied to the analysis of 57Fe Mössbauer spectra

The performance of proposed antihydrogen spectroscopy or gravity experiments will crucially depend on the temperature of the initial antihydrogen sample. Measurements by ATRAP and ATHENA have shown that antihydrogen produced with the nested-trap technique is much hotter than the temperature of the surrounding trap. Therefore, novel schemes for antihydrogen recombination as well as for the pre-cooling of antiprotons are being considered. We are investigating a possible antiproton cooling technique based on the laser cooling of negative osmium ions. If demonstrated to be successful, it will allow the sympathetic cooling of antiprotons—or any negatively charged particles—to microkelvin temperatures. As a first milestone toward the laser cooling of negative ions, we have performed collinear laser spectroscopy on negative osmium and determined the transition frequency and the cross-section of the relevant bound–bound electric-dipole transition.     

<Emphasis Type="Italic">In-situ</Emphasis><Superscript>57</Superscript>Fe Mössbauer characterization of iron oxides in pigments of a rupestrian painting from the Serra da Capivara National Park,in Brazil,with the backscattering Mössbauer spectrometer MIMOS II

It is reported the use of the miniaturized portable ⁵⁷Fe Mössbauer backscattering spectrometer MIMOS II to perform in situ measurements in the archaeological site known as Toca do Boqueirão do Sítio da Pedra Furada (BPF), in Serra da Capivara National Park, in order to specifically examine shades of dark red pigments and compare their differences relatively to the light red part of the same painting. The hyperfine Mössbauer parameters reveal that the dark red area of the rupestrian painting is composed of three populations of hematite and of a small proportion of maghemite, whereas the light red are of the same painting contain hematite mixed with a small proportion of maghemite and a (super)paramagnetic Fe ³⁺. The Fe content in the dark red area from the rupestrian painting is of approximately twice the amount in the light red of the same prehistoric graphism. The corresponding analysis of red ochre sample collected in the excavation of these archaeological site exhibited two populations of hematite and also a small proportion of maghemite.     

Mössbauer study of 1% <Superscript>57</Superscript>Fe doped ferromagnetic insulator La<Subscript>0.825</Subscript>Ca<Subscript>0.175</Subscript>MnO<Subscript>3</Subscript>

We have employed magnetization measurements, M?ssbauer and ESR spectroscopic techniques, in order to study the ferromagnetic insulating (FMI) compound La_1-xCa_xMnO₃ (x=0.175) doped with 1% ⁵⁷Fe. We have used two samples; one prepared in air which has cation vacancies and a second in inert atmosphere, which is stoichiometric. An abrupt change of the experimental results is obtained, by all techniques, in the ferromagnetic insulating regime, in the temperature region of T_O/O//≈60 K, where an orbital rearrangement is suggested to occur. An analysis of these findings points to an orbital rearrangement transformation. Ferromagnetic resonance reveals considerable differences between stoichiometric and cation deficient samples, indicating anisotropy of the exchange interactions in the former sample with significant temperature dependence, most pronounced in the vicinity of T_O/O//     

Electrochemical properties of Ti-Ni-Sn materials predicted by <Superscript>119</Superscript>Sn Mössbauer spectroscopy

The electrochemical activity of TiNiSn, TiNi ₂Sn and Ti ₆Sn ₅ compounds considered as negative electrode materials for Li-ion batteries has been predicted from the isomer shift- Hume-Rothery electronic density correlation diagram. The ternary compounds were obtained from solid-state reactions and Ti ₆Sn ₅ by ball milling. The ¹¹⁹Sn Mössbauer parameters were experimentally determined and used to evaluate the Hume-Rothery electronic density [e _av]. The values of [e _av] are in the region of Li-rich Li-Sn alloys for Ti ₆Sn ₅ and outside this region for the ternary compounds, suggesting that the former compound is electrochemically active but not the two latter ones. Electrochemical tests were performed for these different materials confirming this prediction. The close values of [e _av] for Ti ₆Sn ₅ and Li-rich Li-Sn alloys indicate that the observed good capacity retention could be related to small changes in the global structures during cycling.