Backscattering Mössbauer spectroscopy of Martian dust

We report on the determination of the mineralogy of the atmospherically suspended Martian dust particles using backscattering ⁵⁷Fe Mössbauer spectroscopy on dust accumulated onto the magnets onboard the Mars Exploration Rovers. The spectra can be interpreted in terms of minerals of igneous origin, and shows only limited, if any, amounts of secondary minerals that may have formed in the presence of liquid water. These findings suggest that the dust has formed in a dry environment over long time in the history of the planet.     

Identification of substitutional and interstitial Fe in 6H-SiC

Iron impurities on interstitial (Fe_i) and substitutional sites (Fe_S) in SiC have been detected by ⁵⁷Fe emission Mössbauer spectroscopy following implantation of radioactive ⁵⁷Mn⁺ parent ions. At temperatures <900 K two Fe_i species are found, assigned to quasi-tetrahedral interstitial sites surrounded by, respectively, four C (Fe_i,C) or Si atoms (Fe_i,Si). Above 900 K, the Fe_i,Si site is proposed to “transform” into the Fe_i,C site by a single Fe_i jump during the lifetime of the Mössbauer state (T _1/2?=?100 ns). Fe_i,C and substitutional Fe_S sites are stable up to >1,070 K.     

The Characterization of FeZSM-5 by 57Fe Mössbauer Spectroscopy: Sensitivity Towards Nitrogen

Hyperfine Interactions - Mössbauer spectra were recorded at 4.2 K of an FeZSM-5 zeolite that has been treated with nitrogen at 623 K. Changes in the sample environment clearly show the...     

Iron-57 Mössbauer spectroscopy study of phases in the CaZrTi2−2x Nb x Fe x O7 zirconolite system

Materials of composition CaZrTi_2?2x Nb _x Fe _x O₇ with the fluorite-related zirconolite structure have been prepared. The ⁵⁷Fe Mössbauer spectra show that iron is initially located in the five co-ordinate cation sites. As the iron content increases the iron enters the octahedral sites until, at a composition CaZrTi_0.4Nb_0.8Fe_0.8O₇, ca. 50% of the iron is five co-ordinate and the remainder is located in the octahedral sites.     

57Fe Mössbauer spectroscopy on the cyclic spin-cluster Fe6(tea)6(CH3OH)6

We present ⁵⁷Fe Mössbauer spectroscopy experiments on the cyclic spin-cluster Fe₆(tea)₆(CH₃OH)₆ (tea = triethanolaminato(-3)). In former studies, the spin cluster has been treated as a homogenous, quasi-one-dimensional spin S=5/2 Heisenberg antiferromagnet. Our experiments reveal spectra, which consists of two different quadrupolar doublets. In consequence, there are two different Fe sites among the hexanuclear iron spin-cluster.     

Experimental observation of vibrations produced by pulsed laser beam in MgO:57Fe

We report the first observation of a laser-produced vibration with the aid of Mössbauer techniques. Thin platelets of MgO single crystals were doped by diffusion of ⁵⁷Fe atoms. The illumination of the MgO:⁵⁷Fe sample with a pulsed Nd:YAG laser produced a significant broadening of the Mössbauer spectrum. In order to find out what caused these changes, we performed a series of time-domain experiments, in which the Mössbauer spectra were collected only during a 2.5 μs gate interval. This gate interval was swept from 5 μs to 190 μs over the time interval between the two laser pulses. After laser irradiation, the position of the Mössbauer line was found to be changing in time as a decaying oscillations of well-defined frequency, which can be due to the vibration of the sample induced by the laser pulse.     

Creation of ferromagnetic properties of V–Fe and Zr–Fe alloys by hydrogen absorption

The results of investigations of V_1?y Fe _y H _x and Zr_1?y Fe _y H _x alloys by ⁵⁷Fe Mössbauer spectroscopy are presented and discussed in view of hydrogen ability to create ferromagnetic properties of the alloy. The results indicate two different possibilities of hydrogen influence on the hyperfine magnetic field. Hydrogen absorption causes the ferromagnetic behaviour of the alloys at significant lower iron concentration compared to the concentration of magnetic transition in binary alloys. The main reason for such behaviour is the anisotropic lattice expansion in hydrogenated V–Fe and Zr–Fe alloys as well as the decomposition of paramagnetic Zr-rich intermetallic compounds in the aftermath of the strong electron affinity of hydrogen for zirconium. These trends give rise to growth of magnetic clusters of Fe atoms so strong that they can participate in the overall magnetic properties of the system under investigation.     

Debye temperature and magnetic ordering in K x Ba1−x Fe2S3

⁵⁷Fe Mössbauer measurements are reported for the series K _x Ba_1?x Fe₂S₃, x ≤ 0.3, at temperatures between 4.2 K ≤ T ≤ 294 K. A decrease of the Debye temperature from 435 to 405 K with x, indicates a weakening of the stiffness of the Fe sublattice. The ordering temperatures, taken from the appearance of magnetic hyperfine splitting in the spectra, are approximately 40 K lower for x ≥ 0.1. The values of the centre shift and the small temperature dependence of the quadrupole splitting strongly supports that similar to the border compound BaFe₂S₃ also the K containing samples should be characterised as mixed valence compounds.     

237Np and 57Fe Mössbauer study of NpFeGa5

⁵⁷Fe and ²³⁷Np Mössbauer ōmeasurements have been performed for NpFeGa₅, which is one of the so-called neptunium 1-1-5 compounds. The ⁵⁷Fe Mössbauer spectra below T _N = 118 K show the magnetically ordered state. The magnitude of the hyperfine magnetic field at the ⁵⁷Fe nucleus is determined to be 1.98 ± 0.05 T at 10 K. From the ²³⁷Np Mössbauer spectrum at 10 K, the hyperfine magnetic field at the ²³⁷Np nucleus is 203 T and the hyperfine coupling constant is determined to be 237 T/μ_B using the Np atomic magnetic moment of 0.86 μ_B determined by the neutron diffraction study.     

Reactions of 57Mn implanted into solid oxygen

The in-beam Mössbauer spectroscopy using a short-lived ⁵⁷Mn (T _1/2=1.5 min) beam was carried out to study the production of the exotic chemical species of ⁵⁷Fe atoms arising from ⁵⁷Mn implanted into solid oxygen. The obtained spectra can be analyzed by four components of doublets at least, which are assigned to be novel Fe species of FeO, Fe(O₂), (O₂)FeO₂, and Fe(O₂)₂, on the basis of ab initio molecular orbital calculations.     

Study of the electrochemical properties in substituted Li2Ti3O7 ramsdellite

Substituting the ramsdellite compound Li₂Ti₃O₇ has been considered in order to improve the structure stability and performances for its use as electrode material for Li-ion accumulators. Two substitutions have been carried out, Ti/Fe and (Ti, Li)/(Fe,Ni). The presence of ⁵⁷Fe as a local Mössbauer probe is interesting for studying its local environment and the electrochemical mechanisms induced by lithium insertion.     

Iron-based nanocrystalline alloys investigated by 57Fe Mössbauer spectrometry

Soft magnetic nanocrystalline alloys have attracted great fundamental interest in recent years due to their two-phase structural and magnetic behaviour. We review first the reliability of the fitting procedures of spectra obtained by ⁵⁷Fe Mössbauer spectrometry which is a very efficient tool to investigate such materials. Then, we report the common features which characterise the temperature dependence of Mössbauer spectra; the hyperfine field temperature dependence of both the crystalline grains and the intergranular phase is discussed for different crystalline fractions in order to model the magnetic behaviour of the nanocrystalline alloys.     

Mössbauer and SEM study of Fe–Al film

Fe–Al alloy with Fe/Al ratio of 3:1 was first prepared by argon arc melting. It was subsequently coated on glass slide and cellophane tape using an electron beam gun system to have a thickness of 2,000 Å. X-ray diffraction spectrum of the coated sample indicates a definite texture for the film with a preferential growth along the Fe(110) plane. SEM micrographs of the film showed the presence of nano islands of nearly 3?×?10¹²/m² surface density. Composition of different parts of the film was determined using EDAX. Room temperature Fe-57 Mössbauer spectrum of coated sample showed the presence a quadrupole doublet with a splitting of 0.46 mm/s, which is typical of Al-rich iron compounds. MOKE study shows an in-plane magnetic moment.     

Surface oxidation control of nanosized magnetite and Mössbauer measurements

Selected highly homogeneous powders of Fe₃O₄ with different particle size on the nanometer scale (10?±?2 and 3?±?2 nm) obtained by soft-chemical methods were studied by Mössbauer spectroscopy. The study shows clearly the powerful possibilities of Mössbauer spectroscopy to analyze the surface oxidation of nanostructured powders of magnetite. On the other hand, it is shown that for very small superparamagnetic particles the spectrum of magnetite might be quite similar to that of maghemite, making it difficult to distinguish between both phases.     

Mössbauer, X-ray diffraction and magnetization studies of Fe–Mn–Al–Nb alloys prepared by high energy ball milling

Fe₆₀Mn₁₀Al₂₀Nb₁₀, (Fe₆₀Mn₁₀Al₃₀)₉₅Nb₅ and (Fe₆₀Mn₁₀Al₃₀)₉₀Nb₁₀ ball milled powdered alloys were investigated using X-ray diffraction, Mössbauer spectrometry, thermomagnetic (TGM) and magnetization measurements. We studied the influence of Nb content and of different milling times on the structural and magnetic properties. Two main features can be concluded: (1) the FeAlMn induces a BCC phase whatever the Nb content is, and (2) as both increasing Nb content and milling time give rise to an highly disordered state in conjunction with a decrease of the ferromagnetic behavior.     

A novel investigation of tin-doped ferrihydrite nanoparticles

Tin-doped ferrihydrite was synthesized and characterized with powder X-ray diffraction and ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy to obtain diagnostic and structural information. Samples were prepared with doping concentrations (molar percentages) of 0, 10, 25, 40, 50, 60, 75, and 90% tin. As Sn concentration increases, the 110 reflection plane of ferrihydrite shifts to higher d-values, while the 300 plane d-values increase, reach a maximum and then sharply drop. The δ (isomer shift) and Δ (quadrupole splitting) values for ⁵⁷Fe Mössbauer spectra increase, while the Γ (line width) values stay constant. In ¹¹⁹Sn Mössbauer spectra, δ values decrease with increasing tin substitution while Δ and Γ values increase. After 50% Sn has been substituted, the ferrihydrite becomes oversaturated with surface tin and a secondary tin structure is proposed to develop.     

Investigations of grain boundaries in copper using emission Mössbauer spectroscopy

Grain boundaries (GBs) in pure Cu specimens were studied by means of ⁵⁷Fe emission Mössbauer spectroscopy. A spectrum component which can be ascribed to iron atoms at GBs is represented by the single line with isomer shift 0.67 ± 0.05 mm/s. It is interpreted as iron atoms at GB sites with expanded atomic volumes and highly symmetric distribution of surrounding atoms.     

Mössbauer spectroscopy methodology at the cutting-edge of high-pressure research

This paper provides a concise, introductory review intended mainly for Mössbauer spectroscopy (MS) scientists not familiar with the most modern aspects of High Pressure (HP) methodology. Following a short introduction to the 1^st generation HP-MS based on Drickamer’s pressure cells, we describe the principles of the 2^nd generation of HP-MS based on the Diamond Anvil Cell (DAC) including in-situ pressure measurements, the use of the high-specific activity ⁵⁷Co(Rh) point sources, and examples of miniature DAC’s. Finally, we present recent studies carried out with ⁵⁷Fe HP-MS combined with other HP techniques such as resistivity, and synchrotron-based x-ray diffraction, describing unique cases of the breakdown of magnetism and the Mott transition in hematite (Fe₂O₃), pressure-induced spin crossover in Wüstite (FeO), pressure induced Fe²⁺ → Fe³⁺ in Fe(OH)₂, and (P,T) induced inverse? normal spinel transition in magnetite (Fe₃O₄).     

The BM5Se9 phases: Mössbauer studies of the superconductors and the ferromagnets

Syntheses performed in the A₃B/MSe₂ (A = Sb, Ga, Sn) (B = Nb, V, Ta) (M = V, Nb, Ta) systems lead to the formation of B(M/A)₅Se₉ phases which could be ferromagnets or superconductors. It has been shown that the presence of V modifies the superconducting exchanges and allows ferromagnetic couplings. Mössbauer spectroscopy of both ¹²¹Sb and ¹¹⁹Sn gives local electronic structure of the SbNb₅Se₉ superconductor and the Sn_0.94Ga_0.06V_0.30Nb_4.70Se₉ ferromagnet. For the latter compound, a complete study as a function of temperature is carried out showing that the Sn environment is not modified when the ferromagnetic transition occurs. The Debye temperature is calculated and compared to those obtained for other selenide compounds.     

Mössbauer Spectrometer with Novel Moving System and Resonant Detection of Gamma Rays

Temperature-dependent ⁵⁷Fe Mössbauer spectroscopy has been used to elucidate the hyperfine parameters and dynamical behavior of the metal atom in several organo-iron complexes which have one or more η⁵ P₅ ring structures as ligated groups. The spin-lattice relaxation of the (paramagnetic) one-electron oxidation products occurs on a time scale fast compared to τ_1/2 (ME) at temperatures in the range 85 < T < 320 K.