151Eu and57Fe Mössbauer effect studies of magnetic interactions in europium transition element oxides solution

The solid state solutions of europium transition element oxides Eu (Fe0.8M0.2)O₃ (M=Sc,Cr,Mn,Co) are synthesized. The X-ray diffraction of the compound shows that all the compounds possess the perovskite structures. Both the¹⁵¹Eu Mössbauer spectra and the⁵⁷Fe Mössbauer spectra are measured. The hyperfine magnetic field and non-axisymmetric electric field gradient are observed in the¹⁵¹Eu Mössbauer spectrum. The⁵⁷Fe Mössbauer spectrum shows that there are four components of hyperfine fields corresponding to four kinds of different neighbours of the Fe ion.     

A Mössbauer spectroscopy study of the conformational dynamics of native membrane proteins

In a Mössbauer study of non-dehydrated membrane proteins from thermophilic green-blue algae we observed the behavior of the “narrow” and “broad” lines of their Mössbauer spectra during the heating from 80 to 270 K and found that the behavior of the full area S_F under the spectrum resembles that of the Debye-Waller factor and that quadrupole splitting decreases drastically, from Δ = 0.7 mm/s to Δ ≈ 0, as the temperature is increased from 220 to 270 K. The mathematical treatment of the spectra and decomposition into three components corresponding to thermal, diffusional and conformational motions enabled us to explain the temperature-dependent changes in the spectra.     

Artificial neural networks in Mössbauer material science

Mössbauer spectroscopy is a useful technique for characterizing the valencies, electronic and magnetic states, coordination symmetries and site occupancies of the cation. The Mössbauer parameters of isomer shift and quadrupole splitting are useful to distinguish paramagnetic ferrous and ferric iron in several substances, while the internal magnetic field provides information on the crystallinity. In recent years artificial neural networks have shown to be a powerful technique to solve problems of pattern recognition of a mineral from its Mössbauer spectrum, Mössbauer parameters data bank, crystalline structure and magnetic phases of soil from Mössbauer parameters. A computer software named Mössbauer Effect Assistant has been developed. It uses learning vector quantization neural network linked to a Mössbauer data bank that contains Mössbauer parameters of isomer shift, quadrupole spliting, internal magnetic field and the references of the substances. The program identifies the substance under study and/or its crystalline structure when fed with experimental Mössbauer parameters. It can also list the references from the literature by feeding the name of the substance or the author of the publication. Typical application of Mössbauer Effect Assistant in iron-bearing materials Mössbauer spectroscopy is present in user friendly Microsoft Windows environment.     

Study of metal grains extracted from chondrite Tsarev L5 using Mössbauer spectroscopy with high velocity resolution

Study of metal grains extracted from ordinary chondrite Tsarev L5 using Mössbauer spectroscopy with high velocity resolution was made for the first time. Three magnetic and one paramagnetic components were revealed in Mössbauer spectrum of extracted metal. These components were related to correspondent phases of Fe–Ni–Co alloy while only two magnetic components related to metal were revealed in the spectrum of bulk meteorite sample. The results obtained were in agreement with metallographic study of metal grains in meteorite Tsarev L5 which demonstrated the presence of four Fe(Ni, Co) phases.     

Mössbauer study of the NingQiang carbonaceous meteorites

The NingQiang carbonaceous meteorites from the Shan Xi(China) was falling in 1983. In this report, the Mössbauer spectra has been measured for the NingQiang meteorites and the spectra were analysed with computer. The experimental results indentify it as a carbonaceous meteorite of type III. The spectrum shows the principal iron components to be of olivine, magnetite, troilite and phyllosilicate or goethite material. For comparation the Mössbauer spectra of the Allende and Leoville carbonaceous meteorites have been also measured.     

Advances in Mössbauer data analysis

The whole Mössbauer community generates a huge amount of data in several fields of human knowledge since the first publication of Rudolf Mössbauer. Interlaboratory measurements of the same substance may result in minor differences in the Mössbauer Parameters (MP) of isomer shift, quadrupole splitting and internal magnetic field. Therefore, a conventional data bank of published MP will be of limited help in identification of substances. Data bank search for exact information became incapable to differentiate the values of Mössbauer parameters within the experimental errors (e.g., IS = 0.22 mm/s from IS = 0.23 mm/s), but physically both values may be considered the same. An artificial neural network (ANN) is able to identify a substance and its crystalline structure from measured MP, and its slight variations do not represent an obstacle for the ANN identification. A barrier to the popularization of Mössbauer spectroscopy as an analytical technique is the absence of a full automated equipment, since the analysis of a Mössbauer spectrum normally is time‐consuming and requires a specialist. In this work, the fitting process of a Mössbauer spectrum was completely automated through the use of genetic algorithms and fuzzy logic. Both software and hardware systems were implemented turning out to be a fully automated Mössbauer data analysis system. The developed system will be presented.     

Mössbauer line sharpening

A novel analytical method of Mössbauer spectra resolution improvement has been developed. This method gives an opportunity to narrow the effective line of a source and an absorber by simple integral transformations of an experimental spectrum, that is, to transform the Lorentzian linewidth to the Lorentzian power one. The resulting spectrum may be considered as a new experimental one since the statistical error in each point of the spectrum is evaluated exactly. The procedure of sharpening gives many advantages for Mössbauer spectra analysis. To illustrate this, a number of applications of the proposed method is demonstrated.     

The Mössbauer effect data center: A report

The Mössbauer Effect Data Center is unique in its operation and the kind of information services that it provides. It is probably the only user-supported information center in the basic sciences. This has been primarily possible due to the broad support and encouragement the center receives from the international Mössbauer community. This report also discusses the demographics of the Mössbauer community: identifying such items as the most active areas of research in Mössbauer Spectroscopy, where is this research being done and who is doing it. Also, examined is where Mössbauer research investigations are being published. BITNET and other forms of electronic mail are being widely used in the scientific community. This is also the case in the Mössbauer community. Directories and list-servers are being established.     

Mössbauer spectroscopy of disordered magnetic systems

In the given summarizing article, we present the most important aspects of the technique of studying disordered magnetic systems by the Mössbauer effect being developed by us for the broad circle of researchers in magnetism and Mössbauer spectroscopy. The potentialities of this technique in investigating local magnetic characteristics and spin structures of disordered magnetics are assessed by the interpretation of Mössbauer spectroscopy data of various classes of well-studied magnetics (Fe?Al, Fe-V). In the concluding part, we present original results of Mössbauer investigations of binary (Fe?Cr, Fe?Pd and Fe?Au) and quasi-binary (Fe?Pd?Au) alloys characterized by non-trivial macroscopic magnetic properties and complex magnetic phase diagrams.     

Mössbauer studies of frozen aqueous solutions of iron-II chloride

This paper deals with Mössbauer measurements of frozen solutions of FeCl₂ in water in the temperature range from ?180 °C to their melting point. For thermally quenched solutions 3 different states, connected by irreversible transitions, are observed in quadrupole splittings and isomer shifts. For slowly cooled solutions two different phases, connected by an irreversible transition, are likewise observed. In both cases, those phases persistent until the melting point, are identical.     

The Unusual Mössbauer Spectrum of Beryl

The Mössbauer spectra of several aquamarine samples have been obtained in the temperature range of 4.2–500 K. A common feature observed in all room-temperature spectra is the presence of an asymmetric Fe²⁺ doublet (ΔE _Q～2.7 mm/s, δ～1.1 mm/s), with a very broad low-velocity peak. This asymmetry is not caused by preferred orientation since the spectrum collected under the magic angle did not show any difference in the line intensities, nor is it caused by the superposition of a Fe³⁺ doublet. At 4.2 K the spectrum of a deep-blue beryl could be well fitted with three symmetrical doublets, with the major Fe²⁺ doublet accounting for 87% of the total spectral area. At 14 K the symmetry remains, but at 30 K the low-velocity peak is again broad. Surprisingly, the spectrum at 500 K also shows a broad, but symmetrical doublet, with a clear splitting of the lines indicating the presence of at least two Fe²⁺ components. The room-temperature spectrum obtained after the 500 K run shows the same features as before the heating. A meaningful fit for the room-temperature spectrum, as well as an explanation for the temperature dependence of the Mössbauer spectra, are discussed.     

Dynamical after-effects of nuclear decay in Mössbauer resonance

A general expression has been derived for the spectral distribution of Mössbauer radiation in presence of both lattice dynamical and electronic aftereffects of nuclear decay. The expression has been used to calculate Mössbauer spectrum in a possible experimental situation where the decaying atomic state results in a change in hyperfine interactions as well as a change in the binding of the Mössbauer atom in the lattice.     

The magnetic hyperfine interaction of iron atoms isolated in a xenon matrix in the presence of an external magnetic field

The Mössbauer effect has been used to measure the magnetic hyperfine interaction of isolated ⁵⁷Fe atoms in solid xenon with an applied external magnetic field. A field dependent Mössbauer absorption spectrum is observed. The ground state of these iron atoms is a triplet, which is split in the external field. The Mössbauer spectrum was analyzed taking into consideration relaxation effects. For an applied external field of 28 kOe an internal magnetic field at the ⁵⁷Fe nucleus of 700± 15 kOe was observed (external field included).     

Mössbauer spectra of gadolinite and aeschynite

The Mössbauer spectra of the Natural gadolinite and aeschynite at 297K and 81K were measured. The Mössbauer spectrum of the gadolinite consists of one Fe³⁺ doublet and two Fe²⁺ doublets, and the multiple Fe²⁺ doublets in the spectrum of the gadolinite were relating to the next nearest neighbour effect. The Mössbauer spectrum of the aeschynite is composed of one Fe³⁺ doublet and one Fe²⁺ doublet, and this result is in agreement with crystal structure determination.     

197Au Mössbauer study of Au/Ni artificial multilayers

¹⁹⁷Au Mössbauer measurements have been performed at 16 K on the Au/Ni artificial multilayers having three different thickness of the layers those are 10Å Au/10Å Ni, 30Å Au/30Å Ni and 53Å Au/53Å Ni on a 250Å pure Au buffer layer. Mössbauer spectra obtained can be decomposed into mainly two components. One is an unperturbed component having an identical isomer shift value to the bulk Au metal. The other is the component perturbed strongly by the Ni layer indicating a broad contribution at positive velocity side and its intensity depends on the thickness of the Au layer. The spectrum from 10Å Au/10Å Ni multilayer is an entirely perturbed one and its area ratio to the component rising from pure Au buffer layer indicates the large Debye-Waller-factor suggesting the supermodulus effect in this multilayer.     

Optimizing the features of the single-channel analyzer towards improvement of productivity of Mössbauer spectra

The statistical quality (productivity) of the Mössbauer spectra is one of the most important features characterizing the Mössbauer spectrometer. Optimizing the discrimination part of the spectrometer including the novel way of selection represents a route how to increase the spectrum productivity.     

A Mössbauer effect investigation of the magnetic behaviour of (Fe,Co)S1 + x solid solutions

The Mössbauer spectra of (Fe, Co)S_{1 + x} were recorded at room temperature and 4.2 K for samples of varying composition to study the magnetic behaviour of the solid solutions. The Mössbauer spectra are split magnetically at iron concentrations above 16% Fe. For samples with less than 16%Fe, the Mössbauer spectra show no evidence of magnetic splitting down to 4.2 K. The room temperature centre shift data appear to vary continuously with composition and the hyperfine magnetic field decreases with decreasing Fe²⁺ concentration. A Mössbauer spectrum of ⁵⁷Fe:CoS at 4.2 K in an external field of 25 kOe showed no evidence of magnetic splitting beyond that caused by the applied field, indicating a net zero internal field.A high spin to low spin transition in Fe²⁺ is ruled out as being responsible for the observed magnetic behaviour on the basis of the centre shift data. The Mössbauer data are interpreted to indicate a substantial increase in electron delocalization towards the ligands as the 〈M-S〉 distance decreases with decreasing Fe²⁺concentration. This causes a reduction in the magnitude of the internal magnetic field contributions as well as a decrease of shielding of the nucleus, giving rise to the observed Mössbauer parameters.The Mössbauer spectrum of ⁵⁷Fe:CoS at room temperature is compared with the spectrum of FeS above the 6.7 GPa phase transition at room temperature. The similarities of the centre shift and the 〈M-S〉 distance in the two phases indicate that covalency may also be responsible for the observed high pressure behaviour of FeS, and not the presence of Fe³⁺ as was originally suggested.     

Changement de la section d'absorption Mössbauer des noyaux de 57Fe au voisinage du point de Curie dans le nickel

The anomalous temperature dependence of the Mössbauer spectrum area of ⁵⁷Fe in Ni is due to the change of resonance interaction cross-section in the vicinity of the Curie point.     

Characterization of Zn−Fe intermetallic compounds

Zn?Fe intermediate phases have been investigated. The distribution of quadrupole splittings P(QS) was determined from the Mössbauer spectrum: the P(QS) gives evidence for two different iron sites in the γ phase. The analysis of Mössbauer spectrum taken in an applied magnetic field shows the negative sign of electrical field gradients is present.