Mössbauer Study of Oxygenated Iron-Phthalocyanines,a Precursor of Magnetic Storage Material

⁵⁷Fe transmission Mössbauer spectroscopy and X-ray diffractometry were used to study - and -polymorphs of iron phthalocyanines (FePc) to get information about their oxygenation in connection with controlled pyrolysis of flat layered phthalocyanines initiated by radicals at relatively low temperatures, to form acicular carbide particles encaged in carbon. Mössbauer spectroscopy and XRD revealed that the oxygenation of both - and -polymorphs of FePc was successfully achieved. New Mössbauer spectral components (doublets) appeared upon the oxygenation in both and FePc. This can be attributed to iron microenvironments containing oxygen between the layers of iron phthalocyanines.     

The effect of iron doping in La0.8Sr0.2Fe0.05Co0.95O3-δ perovskite

La0.8Sr0.257Fe0.05Co0.95O3- perovskite is investigated by 57Fe transmission and emission Mössbauer spectroscopy, X-ray diffraction, AC magnetic susceptibility and magnetotransport measurements. Temperature dependence of the 57Fe Mössbauer isomer shift, quadrupole splitting, magnetic hyperfine field, line broadening, and relative spectral area is presented in a detailed manner for La0.8Sr0.257Fe0.05Co0.95O3- . The oxidation state of iron is determined to be Fe3+, and the presence of preferential electronic charge compensation Fe3+ Fe4+ over that of Co3+ Co4+ is excluded. Relaxation of iron magnetic moments reflected by the 57Fe Mössbauer spectra of La0.8Sr0.257Fe0.05Co0.95O3- are interpreted as evidence for the existence of superparamagnetic like Co clusters and a corresponding cluster glass magnetic phase formed below T 65 K.     

Pervasiveness of cluster excitations as seen in the Mössbauer spectra of magnetic materials

Magnetic cluster excitations in various physical systems (e.g., soliton bearing one-dimensional solids, metallic alloys, amorphous materials, small particle aggregates, magnetically ordered substances near T_C, transition metal di-chloride graphite intercalation compounds, etc.) are described. Use of Fe-57 Mössbauer effect spectroscopy as a probe of the spin dynamics for inverse autocorrelation times between 10⁷Hz to 10¹⁰ Hz is emphasized. Particular attention is given to systems which exhibit local or long range magnetic order and whose Mössbauer spectra must therefore be described by more than one autocorrelation (or dwell) time for fluctuations between different allowed hyperfine field directions on a given site.     

Investigation of Rust Formed on Steel Surfaces and Related Oxyhydroxides

In order to indentity the corrosion products formed on steel surfaces from ⁵⁷Fe Mössbauer spectroscopy, detailed Mössbauer parameters have been determined for various kinds of iron-oxyhydroxides: -FeOOH, -FeOOH, -FeOOH and -FeOOH. ⁵⁷Fe Mössbauer measurements of the iron oxyhydroxides indicate the following results. Fe occupies a single site in -FeOOH, but below the Néel temperature as at e.g., 300 K the Mössbauer spectrum is always broad, showing a distribution of the strength of the magnetic exchange interactions. Its shape depends on the grain-size and synthetic methods of the specimen. Fe occupies 3 sites in -FeOOH. High-purity reagents of -FeOOH always contain small amounts of -FeOOH and their Néel temperatures depend on the synthetic methods of the specimen. Mössbauer spectroscopy of the synthetic -FeOOH shows very broad distribution of the hyperfine magnetic fields.     

Mössbauer study of sediment alteration produced by heat treatment

Pincenvent (France) cooking-place silt-like sediments have been studied by using Mössbauer spectroscopy and characterized by using X-ray diffraction (XRD). The sediments were treated at 400, 600, 800 and 1000°C under oxidizing conditions. We discuss the results and we suggest a Mössbauer thermometer to be used to recognize the temperatures and atmosphere ancient people used in their cooking-places.Fellow of CONICET, Argentina, on leave, Laboratoire d'Ethnologie Prehistorique, 44 Rue de L'Almiral Mouchez, 75014 Paris, France.     

Synchrotron Mössbauer source of57Fe radiation

A nonradioactive source of Mössbauer radiation is described for use in Mössbauer absorption and scattering spectroscopy. The radiation is generated by synchrotron Xrays in an iron borate single crystal set in diffraction conditions at the Néel temperature (75.3°C). Like a conventional Mössbauer source the new Synchrotron Mössbauer (SM) source emits singleline radiation of about natural linewidth, but in addition the emitted radiation is fully recoilless, highly directed and of pure linear polarization. An extremely high suppression of the electronic scattering is achieved. The latter circumstance allows one to perform Mössbauer experiments using pulsed synchrotron radiation in a steady state mode as in a normal Mössbauer measurement.The theory of the SM source is developed. First Mössbauer spectra obtained with the SM source are shown. Applications of the SM source are discussed.     

Mössbauer spectroscopy with actinide elements

Although formally equivalent to the lanthanide (4f) elements, the light actinides show a much more varied behaviour due to the larger spatial extent and ionizability of the 5f electrons. The application of Mössbauer spectroscopy for the determination of electronic properties of the actinides is outlined. Emphasis is put on high pressure Mössbauer experiments using the 60 keV transition in²³⁷Np to study questions of delocalization of 5f electrons.Work performed under the auspices of the Bundesministerium für Forschung und Technologie, Federal Republic of Germany.     

Iron arachidate Langmuir-Blodgett films: magnetic behavior studied at temperatures down to 4.2 K

Langmuir-Blodgett (LB) multilayers of ferric arachidate on silicon wafers have been investigated by means of conversion electron Mössbauer spectroscopy (CEMS) and absorption Mössbauer spectroscopy (AMS) at different temperatures between 4.2 K and room temperature. At low temperatures we observe antiferromagnetic ordering in the two-dimensional model substance and determined the magnitude and the orientation of the internal magnetic field. We studied the phase transition and found with increasing temperature a slow decrease of the ordered phase, which has completely vanished at 130 K. In the present state it cannot be decided if we just observe superparamagnetic relaxation or if we observe additional effects arising from the low dimensionality of the system. Comparable measurements on small iron arachidate LB-particles have been performed but no significant difference between the films and the small particles can be observed. This has been expected because the two-dimensional structure is mainly preserved in the LB-particles.     

Mössbauer effect study of the effect of gamma irradiation and heat treatment on montmorillonite

Mössbauer spectroscopy was used to study the effect of gamma irradiation and heat treatment on montmorillonite. Samples were irradiated to gamma-ray doses ranging from 10 Gy up to 30 MGy. Other samples were heated to different temperatures from 400 C up to 1350 C. The lattice distortion caused by gamma irradiation could be followed. The phase transformations which occurred through and above the dehydroxilation temperature range could be traced and identified. The Mössbauer results were confirmed by X-ray diffraction results.     

Diffusion studies

Mössbauer spectroscopy represents a unique method to determine the frequency and the vector of diffusion jumps in solids. The elementary diffusion event can thus be studied in a microscopic way. In order to get maximum information experiments have to be performed on single crystals.Mössbauer studies of long-range diffusion, on the one hand, have proved the reliability of the method but also demonstrated the considerable technical effort which is necessary. Investigations of localized diffusion (diffusion in a cage), on the other hand, have been successful in various fields of physics and biophysics.     

Mössbauer Spectroscopy on Nuclear Power Plant Materials

Experimental results of original irradiated reactor pressure vessel surveillance specimens are presented and discussed in the paper. In 1994, the new Extended Surveillance Specimen Program for Nuclear Reactor Material Study was started in collaboration with the nuclear power plant (NPP) Bohunice and NPP Research Institute Trnava (Slovakia). Three batches of special prepared Mössbauer samples (after 1, 2 and 3 years stay in irradiation channels) were measured and interpreted using the new four components approach of Mössbauer spectra evaluation with the aim to observe microstructural changes due to thermal and neutron treatment resulting from operating conditions in NPP. The systematic changes in the relative areas of Mössbauer spectra components were observed and discussed.     

The Mössbauer effect and magnetism

The Mössbauer effect enabled the magnetic hyperfine splitting (hfs) in ferromagnetic solids to be observed directly for the first time. It was quickly extended to measurements on antiferromagnets, ferrimagnets and paramagnets, and is now well established as a probe for the study of magnetic materials. Applications have ranged from the old problem of the state of the iron atoms in ferromagnetic alloys to the new magnetic materials, e.g. amorphous magnets, spin glasses, fine particle magnets and multilayers. Some examples where the Mössbauer effect has made an important contribution are described.     

ИЗУЧЕНИЕ ИНТЕГРАЛЬН ОЙ И ЛОКАЛЬНОЙ ЧУВСТВИТЕЛЬНОСТИ ФО ТОКАТОДОВ И ИХ ВЛИЯНИ Е НА ГОРИЗОНТАЛЬНЫЙ УЧ АСТОК ХАРАКТЕРИСТИК И СЦИНТИЛЛЯЦИОННОГО Д ЕТЕКТОРА

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Ghost lines in Mössbauer relaxation spectra

The appearance in Mössbauer relaxation spectra of ghost lines, which are narrow lines that do not correspond to transitions between real hyperfine energy levels of the resonant system, is examined. It is shown that in many cases of interest, the appearance of these ghost lines can be interpreted in terms of the relaxational averaging of one or more of the static interactions of the ion.     

Mössbauer Study of Iron-Containing Carbon Nanotubes

⁵⁷Fe transmission Mössbauer at temperatures between 18 and 298 K and magnetic measurements have been used to characterize Fe-filled carbon nanotubes which were prepared by pyrolisis of Ferrocene + C₆₀ at atmospheric pressure under an Ar atmosphere at 1050°C. The Mössbauer data have shown that the Fe phases encapsulated within the carbon nanotubes are -Fe, Fe₃C and -Fe. The magnetic results are compatible with the Mössbauer data. Taken together the results allow us to propose a simple picture of the distribution of iron phases within the carbon nanotubes which would consist of an -Fe core surrounded by an -Fe shell, finally covered by an Fe₃C layer.     

Mössbauer hyperfine interactions in thermally treated iron-yttrium oxide systems

Iron-yttrium mixed oxides in varying ratios (YFe 91, 31, 11, 12, 13, and 19) annealed to different temperatures (850, 1000 and 1250 C) have been investigated by Mössbauer spectroscopy down to 85 K. The Mössbauer spectra are complex in nature, showing up to three magnetically split hyperfine patterns in iron-rich (Y Fe 11, 12, 13 and 19) samples; these three components are attributed to characteristic YFeO₃, Y₃Fe₅O₁₂ and hematite. The yttrium-rich samples (YFe 91, 31) show only one six-line spectrum of YFeO₃.     

SYNFOS

An expression for the amplitude of a pulse of synchrotron radiation coherently scattered in the forward direction by a Mössbauer absorber consisting of randomly oriented paramagnetic ironcontaining molecules (for example, a frozen solution of a ⁵⁷Fe protein) in an applied magnetic field is derived from the theory of optics. It is assumed that the hyperfine splittings present in the Mössbauer nuclei can be described in the framework of the spinHamiltonian formalism. In the general case of a thick Mössbauer sample of this kind the response on an incident monochromatic and fully polarized beam cannot be given analytically because of the integrations involved. How nuclear forwardscattering for this general case is evaluated in the program package called SYNFOS is outlined.     

57Fe Mössbauer investigations in the series Fe4−2xRuxSix(1.0≦x≦1.7)

⁵⁷Fe Mössbauer and magnetization studies on a new series Fe_4–2xRu_xSi_x (1.0x1.7) are reported. The system is seen to transform from a collinear ferromagnet for x1.2 to a cluster spin glass for x>=1.54 In the intermediate region the magnetic behaviour of the system, as probed by the Mössbauer effect, is dominated by the presence of clusters and their dynamics. The alloys have large ordering temperatures ( 750 K) throughout the series except for x>1.54 where they drop sharply. The moment values, in contrast, fall sharply from 4.8_B at x=1 to 0.5_B at x=1.6C. The average value of the HF at⁵⁷Fe measured at 15 K does not change significantly throughout the series.     

Distribution of iron atoms in Fe-Mn alloys with the structure of β-Mn

X-ray analysis and Mössbauer spectroscopy were used to study the distribution of iron atoms in Fe-Mn alloys isostructural to -Mn and to determine the iron concentrations in the positions 8(c) and 12(d) of the -Mn structure in alloys of different compositions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 86–89, March, 1981.     

Mössbauer spectroscopy with the 93 keV-resonance in67Zn

The procedures and results of high resolution Mössbauer experiments performed with the 93.3 keV resonance in absorbers of⁶⁷ZnO,⁶⁷ZnS (both wurtzite and sphalerite structures),⁶⁷ZnSe,⁶⁷ZnTe and⁶⁷ZnF₂ are reported. An essentially linear dependence between the isomer shift and the Pauling electronegativity of the ligands was found. A value of r ²=+11×10^–3 fm² is estimated. The Mössbauer parameters for both ZnS structures are equal within present limits of error. In particular, no quadrupole interaction was observed in the wurtzite modification. This indicates a nearly identical local symmetry at the Zn site in the two ZnS structures.Work supported by the Bundesministerium für Forschung und Technologie, Federal Republic of Germany and the Kernfor-schungszentrum Karlsruhe