57 Fe Mössbauer and X-ray characterisation of sandstones

Sandstones from the Free State province in South Africa have been mined and processed mainly by small scale and artisanal miners in the rural areas. In the present investigation basic fire proof and water absorption tests, X-ray and γ-ray based characterisation techniques were used to study the sandstones. The collected samples were grouped according to their apparent colour in day light conditions and the elemental analysis showed the presence of a high amount of oxygen (>52%) and silicon (>38%) with Mn, Al, Fe and Ca as major elements in proportions related to the colour distribution of the various sandstones. The uniaxial compressive stress was found to be the highest (56 MPa) for the greyish sandstone and the lowest (8 MPa) for the white sandstone sample, also associated with the lowest (Al+Fe)/Si value of 0.082. The humidity test showed that the 6 % water absorption was lower than the recommended ASTM value of 8 %. The sandstone samples were also subjected to various high temperatures to simulate possible fire conditions and it was found that the non alteration of the mineral species might be one of the reasons why the sandstones are regarded as the most refractory amongst the building materials typically used. Mössbauer spectroscopy revealed that iron is present in all the sandstones, mainly as Fe^3?+? with the black sandstone showing an additional presence of 3 % Fe^2?+? indicating that a higher iron content coupled to higher silicon content, contributes to an increase in the uniaxial compressive strength.     

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.     

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.     

57Fe Mössbauer investigations of manganese-containing spinels

Cation distributions and related order-disorder phenomena in the naturally occurring Mn-spinels: iwakiite, galaxite and franklinite, have been investigated by means of⁵⁷Fe Mössbauer spectroscopy. Previous measurements on an iwakiite sample indicated the existence of Mn-rich and Mn-poor regions. This interpretation has been confirmed in this investigation by further measurements on annealed iwakiite samples. The⁵⁷Fe Mössbauer spectrum of galaxite from Bald Knob, NC, is a well-resolved quadrupole doublet and indicates the presence of a single crystallographic Fe³⁺ species. A galaxite sample from Thailand exhibited a complex spectrum of Fe²⁺ and Fe³⁺ quadrupole doublets: This sample has been misidentified and should be regarded as a member of the (Mg, Fe)(Al, Fe)₂O₄ series. The⁵⁷Fe hyperfine parameters of a rare franklinite from Längban, Sweden, are very close to those for synthetic zinc ferrite, confirming electron microprobe results of an unusually high zinc content.     

Mössbauer spectroscopy on57Fe: NaCl crystals

Mössbauer absorbtion spectra of⁵⁷Fe-doped NaCl crystal were measured and correlated with an adequate electric field gradient computation to describe the dipolar complexes occuring at the decay of Suzuki-phase under thermal treatment and X-ray irradiation. An electrostatic potential of the type was taken into account in the evaluation of EFG tensor.     

57Fe Mössbauer spectra study of coated α-Fe2O3 nanoparticles

Nano-sized -Fe₂O₃ particles coated with polar organic molecules have been studied using the Mössbauer spectroscopy method. The -Fe₂O₃ nanoparticles were prepared by the microemulsion method. The average particle size of the Fe₂O₃ particles is about 24 Å. Because the particle size is so small that the Mössbauer spectra of the -Fe₂O₃ samples only consist of a quadrupole-split central line. It was proved that the Isomer Shifts (DIS) and the Quadrupole Splitting (DQS) changed as the refluxing time prolongs and the refluxing temperature increases during the preparation of the Fe₂O₃ nanoparticles, which implied an enhancement of the surface electrofield gradient formed by the surface coated polar molecules during the refluxing process.     

Magnetization and Mössbauer studies of 57Fe doped SrCoO3

⁵⁷Fe (1%) doped SrCoO₃ obtained by high-pressure method, has been investigated by magnetization and Mössbauer spectroscopy studies (MS) in the temperature range 4.2 K to 300 K. The ferromagnetic ordering temperature T _C obtained is 272(2) K. Isothermal magnetization curves have been measured at various temperatures, from which the saturation moments (M _sat) have been deduced. The ⁵⁷Fe MS spectra display standard six-line patterns with an isomer shift typical of Fe^3?+? and a very small quadrupole splitting (QS = 0.14(1) mm/s above T _C). The magnetic hyperfine field at 4.2 K is 276(1) kOe. The temperature dependencies of the iron hyperfine field and M _sat (1.83 µ _B at 5 K) are almost identical. This shows that the Fe^3?+? is replacing Co^4?+?, both of the same electronic configuration. They also interact similarly, namely the Fe–Co exchange is almost identical to the Co–Co exchange.     

Mössbauer study of FINEMET with different permeability

Stress field and magnetic field annealed FINEMET ribbons were investigated by ⁵⁷Fe Mössbauer spectroscopy, magnetic and XRD methods. The change in relative areas of the 2nd and 5th lines in the Mössbauer spectra indicated significant variation in magnetic anisotropy due to the different annealing. High velocity resolution Mössbauer spectroscopy was also used to control the model applied for the evaluation of Mössbauer spectra. A correlation was found between the permeability and the magnetic anisotropy of the annealed FINEMET samples. This can be applied to predict production parameters of FINEMET ribbons with more favorable soft magnetic properties for technological applications.     

238U and 57Fe Mössbauer Spectroscopic Study of UFe2

We have performed ⁵⁷Fe and ²³⁸U Mössbauer measurements of UFe₂ in order to investigate its magnetic properties. From the results of ⁵⁷Fe Mössbauer spectroscopy, the ferrromagnetic ordering at 167 K is caused by the iron 3d-electrons, which hybridize strongly with the uranium 5f-conduction electrons. It is also clarified from the results of ²³⁸U Mössbauer spectroscopy that there are no magnetic moments on the uranium atoms.     

57Fe and119Sn Mössbauer investigations on some substituted barium hexaferrites

⁵⁷Fe and¹¹⁹Sn Mössbauer measurements have been carried out on powder samples of three differently substituted M-type barium hexaferrites. By⁵⁷Fe Mössbauer measurements in an external magnetic field applied parallel to the -ray direction, we found a canted spin structure for all samples. Furthermore, we detected a strong preference of the Sn⁴⁺ ions for the 4f₂ sites. From⁵⁷Fe Mössbauer measurements aboveT _N, we conclude that the substitution does not influence the 2b sites. The analysis of the magnetically split¹¹⁹Sn Mössbauer spectra at room temperature in the case of the Co-Sn and Zn-Sn substituted samples shows a strong difference between the two. The spectra were interpreted due to the different surroundings of the Sn⁴⁺ ions.     

Relaxation Mössbauer spectra of polymer composites with magnetic nanoparticles

It is shown that the shape of Mössbauer spectra of composites based on single-domain magnetic particles is defined to a greater degree by interparticle interactions rather than the superparamagnetic properties of individual particles. The characteristic features of the spectra of such systems are described and shown to be adequately described within a three-level relaxation model.     

57Fe Mössbauer spectroscopic study of nanostructured zinc ferrite

Nanosize zinc ferrite particles, prepared by nitrate method, were investigated by XRD, TEM, ⁵⁷Fe Mössbauer spectroscopy and VSM. The average particle size in this system varies from 10 to 62 nm as the sintering temperature increases from 300°C to 1,000°C. The lattice parameters in this system are almost constant at a value of ～8.41 Å. The Mössbauer spectra of all the sintered samples show a single doublet. The Mössbauer hyperfine parameters show little change with the change of sintering temperature. The doublets are ascribed to the presence of superparamagnetism in this system, which is also corroborated by the VSM measurements.     

57Fe Mössbauer study of new multiferroic AgFeO2

The present work reports results of the ⁵⁷Fe Mössbauer measurements on AgFeO₂ powder sample recorded at various temperatures including the points of both magnetic phase transitions. The ⁵⁷Fe Mössbauer spectra of AgFeO₂ measured in the paramagnetic range (T > T _N1) consist of one quadrupole doublet with rather high quadrupole splitting of Δ_300K = 0.66 ± 0.01 mm/s for Fe³⁺ ions. In order to predict the sign of electric field gradient (EFG) at ⁵⁷Fe nuclei, we calculated the lattice contribution to the electric field gradient (EFG) at ⁵⁷Fe nuclei, which emphasized the importance of the dipolar contributions, with resultant oxygen polarizabilities in the range of α _O = 0.83 ų, in agreement with the results obtained previously for other delafossite-like oxides. In the temperature range of T _N2 < T < T _N1, Mössbauer spectra gave clear evidence for the existence of a distribution of the hyperfine magnetic fields H _hf at ⁵⁷Fe nuclei. We present the results of a model fitting of the spectra based on an assumption of the cycloid magnetic structure of AgFeO₂ at T < T _N2. The obtained data were analysed in comparison with published data on Mössbauer studies of oxide multiferroics.     

Mössbauer study of 57Fe in GaAs and GaP following 57Mn+ implantation

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken ⁵⁷Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive ⁵⁷Mn^?+? ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T?> 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.     

Mössbauer and PAC studies of nanocrystalline Fe

High-purity Fe powder was mechanically milled under argon at ambient temperature using an SPEX 8000 mill. The local atomic and magnetic structure was studied using⁵⁷Co/Fe Mössbauer and¹¹¹In/Cd perturbed angular correlations (PAC) spectroscopies. After 32 hours of milling, X-ray diffraction revealed effective grain diameters of 18 nm and energy-dispersive X-ray analysis indicated a Cr impurity concentration of 5%, presumably introduced by mechanical attrition of steel ball bearings used for milling. In addition to a spectral component very similar to bulk iron metal, the Mössbauer spectra exhibited hyperfine field shifts attributed to the Cr impurities. PAC spectra on Fe milled for 5 h, with no contamination, exhibited two components: (1) A slightly broadened magnetic interaction attributed to interior, defect-free sites of In/Cd probes with a mean hyperfine field slightly greater than in macroscopic grains. The defect-free site fraction grew appreciably during milling, even though In is essentially insoluble in Fe. (2) An indistinct signal due to mixed magnetic and quadrupole interactions attributed to probes at surface or other defect sites.     

Spreadsheet based analysis of Mössbauer spectra

Using spreadsheet programs to analyse spectral data opens up new possibilities in data analysis. The spreadsheet program contains all the functionality needed for graphical support, fitting and post processing of the results. Unconventional restrictions between fitting parameters can be set up freely, and simultaneous analysis i.e. analysis of many spectra simultaneously in terms of model parameters is straightforward. The free program package Vinda – used for analysing Mössbauer spectra – is described. The package contains support for reading data, calibration, and common functions of particular importance for Mössbauer spectroscopy (f-factors, second order Doppler shift etc.). Methods to create spectral series and support for error analysis is included. Different types of fitting models are included, ranging from simple Lorentzian models to complex distribution models.