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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Volume and surface oxidation of basalt

Natural, Fe²⁺-rich basalt glass (quenched lava) was heat treated as glass pieces and glass powder in air, in 6.0 Ar and in a 9×10^?6 mbar vacuum below temperatures of significant crystallization to access volume and surface oxidation by ⁵⁷Fe Mössbauer spectroscopy. While no oxidation occurs upon heating in vacuum, the amount of Fe³⁺ formed in powder (surface oxidation) is about 10 times higher than in pieces (volume oxidation), and surface oxidation is of the same order in air and Ar. This effect is assigned to chemisorption of water or CO₂. Crystalline basalt, investigated by wet chemistry, includes five glass pieces treated above T of crystallization in air and in 6.0 Ar, and three lava samples of increasing depth up to 9 cm of lava lobes. The high Fe₂O₃ of all these crystalline samples is explained as a stabilization of Fe³⁺ due to the change of the local electronic environment in the course of crystallization; volume oxidation therefore appears to be independent on the environmental atmosphere.     

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.     

Step-shape angular spin distribution in layered systems by Fe Mössbauer spectroscopy: A general treatment

In the so-called ‘step-shape’ angular spin distribution model for layered systems, the non-collinear directions of the atomic magnetic moments are confined to the film plane and form a homogeneous fan spanning inside an (in-plane) angular interval Δφ centered at an angle φ₀. A general approach for deriving the two parameters φ₀ and Δφ via ⁵⁷Fe Mössbauer spectroscopy measurements is discussed. The analysis extends our previously reported treatment, which assumed that the angular aperture Δφ develops symmetrically versus a fixed direction φ₀ (e.g., the in-plane easy axis of magnetization) oriented either along or perpendicular to the in-plane projection of the Mössbauer γ-ray direction. The proposed approach is also applicable for those cases when not only the spin aperture Δφ is changing but also the aperture center φ₀ is rotating under the influence of different external parameters, such as applied field, temperature, stress, etc. The method is suitable for applications to nanoscale layered heterostructures with in-plane uniaxial or unidirectional magnetic anisotropy. The method is applied to experimental data obtained on a 2-nm thick defected Fe layer with in-plane magnetic texture.     

57Fe Mössbauer Studies of Sr2−x Ca x FeReO6 Double Perovskite Compounds

Hyperfine Interactions - We present a 57Fe Mössbauer study of the Sr2?x Ca x FeReO6 double perovskite series, with x=0, 0.1, 0.2, 0.5, 1.0, 1.5 and 2.0. The analysis at 300 and 16 K...     

Magnetic properties of metallic glasses of the type Fe80−x Pd x B20 and Fe80−x Pt x B20

Amorphous alloys of the type Fe_80???xPd_xB₂₀ and type Fe_80???xPt_xB₂₀ for 0?≤?x?≤?50 have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy and magnetisation measurements in temperatures from 4.2 up to 300 K. Curie temperatures and crystallisation temperatures are found by DTMG-DTA method. Mössbauer spectroscopy magnetic field is observed to visible increase for x?=?1 and 1.5% at room temperature for Pd, while a decrease is observed for higher x values. Curie temperature for Pd alloys has a maximum at x?=?4 with T _C?=?753 K, which supports enforcing influence of Pd at low concentrations of Pd for magnetic interactions. We discuss different explanations for these measurements and compare with other findings for high Pd concentrations and alloys with Pt instead of Pd.     

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.     

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.     

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).