Mössbauer study of Fe in GaAs following 57Mn + implantation

The metastable 2S state in muonic hydrogen is particularily interesting because a measurement of the Lamb shift could reduce the uncertainty in the proton charge radius by an order of magnitude. The most important prerequisite for such a measurement is a sufficiently large population and lifetime of the 2S state. We have determined the long-lived and short-lived 2S population, the deexcitation mechanisms and lifetimes, and the cascade time in μp.     

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.     

Time-resolved Mössbauer spectra obtained after 57Mn implantation in Si

A new detector system for the coincidence technique between Mössbauer γ-rays and energetic β-rays originating from ⁵⁷Mn has been developed for in-beam Mössbauer spectroscopy using ⁵⁷Mn implantation. This system enables time-resolved Mössbauer measurements of ⁵⁷Fe at various elapsed times after β ^?-decay of ⁵⁷Mn with sufficient quality. We applied this system to the time-dependent measurement of the site distributions of dilute Fe atoms in n-type Si. It was suggested that Fe atoms were already located at substitutional and interstitial positions in Si within a time of about 100 ns after the β ^?-decay of ⁵⁷Mn, and that the occupancy ratio between these positions was hardly dependent on the elapsed time after the β ^?-decay.     

Fe57 Mössbauer study in cobalt substituted magnetite

The Mössbauer effect has been studied in the mixed ferrites Co _x Fe_3–x O₄ (forx=0.8, 0.9 and 1) with the spinel structure in the temperature range between 78 and 380 K. The composition withx=1, showed an expected Zeeman spectrum with two overlapping magnetic hyperfine patterns related to the Fe³⁺ ions in tetrahedral and octahedral sites. While for samples withx=0.8 and 0.9 the Mössbauer spectrum for each compound was successfully analysed into three different patterns corresponding to the ferric ions placed at the tetrahedral and octahedral sites and ferrous ions at the octahedral sites, indicating no electron transfer between Fe³⁺ and Fe²⁺, where the quantity of cobalt is sufficiently large to be located at the six nearest neighbours to ferrous ions. The Mössbauer effect parameters were calculated for these observed sites and their variation with temperature reported. The reduced hyperfine magnetic fields of the Fe³⁺ (B) ions were found to follow the Brillouin curve forS=5/2 and one third power law. The magnetic ordering temperature was determined to be 815 K and the possible magnetic interactions were discussed.     

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.     

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 Lu2Fe3Si5 iron silicide superconductor

With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of ⁵⁷Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. To this end, the iron-based superconductor Lu₂Fe₃Si₅ has been studied by ⁵⁷Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (T_c=6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. The value of Debye temperature was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near T_c, nor phonon softening were observed.     

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 study of La0.67Ca0.33Mn1 − x Fe x O3 CMR system

The structural changes of near-equiatomic α-FeCr alloys, ground in a vibratory mill in vacuum and in argon, were followed as a function of milling time. An amorphous phase forms in both cases but at a much faster rate when milling in argon than when milling in vacuum. Amorphisation by ball-milling of α-FeCr alloys is deduced to be an intrinsic phenomenon which is however speeded-up by oxygen. The amorphous phase crystallizes into a bcc Cr-rich phase and a bcc Fe-rich phase when annealed for short times.     

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.     

In-beam Mössbauer study of 57Mn implanted into a low-temperature xenon

The in-beam Mössbauer spectrum of ⁵⁷Mn implanted into a Xe solid at 14 K was measured. Four singlets were observed in the spectrum, assigned to ⁵⁷Fe^?+? (3d⁷), ⁵⁷Fe^?+? (3d⁶4s¹), ⁵⁷Fe⁰ (3d⁶4s²), and ⁵⁷Fe⁰ (3d⁷4s¹). The assignments were in agreement with calculated electron densities at nuclei reported in the literature. The β-decay of ⁵⁷Mn did not disturb the surrounding Xe lattice, showing a singlet peak, and the excited states were stabilized in the time range of the Mössbauer measurements of ~100 ns. The production mechanism was explained in terms of the reduction of ⁵⁷Mn ^x?+? and ⁵⁷Fe ^y?+? ions by free electrons in the Xe matrix.     

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.     

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 magnetic order in RBa2Fe3O8

Complete replacement of copper by iron in RBa₂Cu₃O₇ leads to RBa₂Fe₃O₈ (R=Y, rare earth). Mössbauer spectroscopy measurements of⁵⁷Fe and¹⁵¹Eu in RBa₂Fe₃O₈ (R=Y, Eu, Ho, Er) at temperatures 4.2–800 K have been performed. Some of the spectra reveal two inequivalent iron sites, probably corresponding to iron in the Fe(2) site (fivefold oxygen coordination) and in the Fe(1) site (octahedral oxygen coordination). In all compounds the iron moments order antiferromagnetically at the same Néel temperatureT _N720 K. The¹⁵¹Eu Mössbauer spectra of EuBa₂Fe₃O₈ show that the Eu ion is trivalent and exposed to a small exchange field from the iron sublattices.     

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.     

Iron nano-clusters in ytterbium films: a 57Fe Mössbauer spectroscopic study

We have performed a Mössbauer study on iron clusters that are formed in ytterbium films prepared by vapor co-deposition onto kapton substrates kept at room temperature. The film thicknesses were chosen in a range between 2.5 and 2.8 $\upmu$ m. XRD of the films reveals a mixture of fcc- and hcp-like ytterbium. Iron concentrations were between 0.3 and 5 at %. All samples reveal hyperfine spectra attributed to only two types of iron clusters with well defined hyperfine parameters. The clusters are supposed to be formed at boundaries of hcp- and fcc-like grains. In addition there is found a small contribution from monomeric iron. Spectra taken at 4.2 K reveal a complex distribution of magnetic hyperfine fields. The dynamic origin of the spectral shape is supported by susceptibility data revealing spin-freezing at temperatures below ca. 10 K. This proves that the iron clusters have sizes on the order of nm.     

57Fe Mössbauer study of the Nurina–003 ordinary chondrite meteorite

Nurina–003 is a Group LL5/br Ordinary Chondrite meteorite which was recovered in the Nullarbor Desert (Australia) in 1986. The degree of weathering is classified as moderate to severe. We have characterised the Fe-bearing phases in Nurina–003 by ⁵⁷Fe Mössbauer Spectroscopy over the temperature range 5–295 K. The spectra are dominated by Olivine and also contain Pyroxene, Troilite and a Ferric component that is (super)paramagnetic at 295 K. We clearly see the effects of the magnetic ordering of the Olivine phase in the 5 K spectrum.