Mössbauer study of nanocrystalline Ni–Zn ferrite

Ni_1−xZn_xFe₂O₄ (0.0⩽x⩽1.0) nanoparticles have been prepared by the polyvinyl alcohol (PVA) sol–gel method. The lattice parameter of Ni–Zn nanoparticle is larger than that of the bulk material. The Mössbauer spectra of the samples showed the presence of ultrafine particles exhibiting superparamagnetic relaxation at room temperature and an ordered magnetic structure at 77 K.     

Mössbauer study of tektites

Room temperature ⁵⁷Fe Mössbauer spectroscopy has been used to investigate the structural and oxidation state of Fe in tektites from different strewn fields. Spectra have been analyzed in terms of two quadrupole splitting distributions corresponding to Fe^3?+? and Fe^2?+?. All tektites show similar distribution of quadrupole splitting. Each distribution has one peak. The Fe^2?+? sites show a narrow region of Mössbauer line shift (δ) and quadrupole splitting (ε), δ?= 1.02–1.10 mm/s and ε?= 0.85–1.00 mm/s relative to α-Fe. These values have been assigned to intermediate coordination between tetrahedral and octahedral. The Fe^3?+? sites show wider regions of hyperfine parameters: δ?= 0.25–0.45 mm/s and ε?= 0.65–0.90 mm/s. The Fe^3?+?/Fe^2?+? ratio was found to be 0.05–0.15.     

Mössbauer effect study of Ni1−xCuxMnyFe2−yO4 system

The Mössbauer effect technique has been employed for the study of magnetic properties of spinel series Ni_1?xCu_xMn_yFe_2?yO₄ with 0.0≤x≤1.0, and y=0.6. The substitution of Mn³⁺ and Cu²⁺ ions results in a slight decrease of the hyperfine field at B‐ as well as A‐sites. The area ratio of Fe³⁺ ions at the A‐ and B‐site at 77 K indicates that Cu²⁺, Ni²⁺ and Mn³⁺ ions occupy the octahedral sites in an evidence for complete inverse spinel in this system. The temperature dependence of the hyperfine parameters has been studied for composition with x=0.5 where Nèel point T_N and Debye temperature θ_D are found to be 650 and 679 K, respectively. The temperature dependence of the sublattice magnetization σ(T) obeys a one‐third‐power law in the range 0.5N<0.99.     

A Mössbauer effect study of MgFe2O4

A slowly cooled sample of the ferrimagnetic spinel MgFe₂O₄ has been studied with ⁵⁷Fe Mössbauer spectroscopy over a wide temperature range both with and without high magnetic fields. The observed temperature dependence of the A and B site hyperfine parameters is discussed. Conclusions about the spin structure, the magnetic exchange interactions and the supertransferred hyperfine fields are presented.     

Mössbauer study of natural wolframites

Natural Wolframite, (Fe _x Mn_1?x )WO₄ withx=0.95 to 0.41, obtained from seven different sites of two quartz-wolframites deposits of Degana and Sirohi in Rajasthan. India, have been studied by Mössbauer spectroscopy down to 20 K. X-ray diffraction studies with a monochromatic Cu radiation (λK_a-1.5405 Å), were carried out to determine the value ofx. The Mössbauer spectra of all seven samples were recored at 300, 200, 100, 50, 40, 30 and 20 K, and were least square fitted for different sites. The Mössbauer parameters are attributed to a high spin ferrous ion in a quite distorted octahedral symmetry, and only one sextet has been resolved below transition temperature.     

Mössbauer study of Slovak meteorites

⁵⁷Fe Mössbauer spectroscopy was used as an analytical tool in the investigation of iron containing compounds of two meteorites (Rumanová and Ko?ice) out of total of six which had fallen on Slovak territory. In the magnetic fraction of the iron bearing compounds in the Rumanová meteorite, maghemite, troilite and Fe-Ni alloy were identified. In the non-magnetic fraction silicate phases were found, such as olivine and pyroxene. The paramagnetic component containing Fe^3?+? ions corresponds probably to small superparamagnetic particles. The Ko?ice meteorite was found near the town of Ko?ice in February 2010. Its magnetic fraction consists of a Fe-Ni alloy with the Mössbauer parameters of the magnetic field corresponding to kamacite α-Fe(Ni, Co) and troilite. The non-magnetic part consists of Fe^2?+? phases such as olivine and pyroxene and traces of a Fe^3?+? phase. The main difference between these meteorites is their iron oxide content. These kinds of analyses can bring important knowledge about phases and compounds formed in extraterrestrial conditions, which have other features than their terrestrial analogues.     

Mössbauer study of Hungarian phlogopites

Ultramafic xenoliths of mantle origin occur in Hungarian Cretaceous lamprophyres. The aim of the present work was to determine the iron positions and their occupancy in phlogopites originated from ultramafic xenoliths by the help of Mössbauer spectroscopy. On the basis of the evaluation of the Mössbauer spectra Fe _M1 ²⁺ , Fe _M2 ²⁺ , Fe _M2 ³⁺ and Fe _M1 ³⁺ (or in some cases Fe_tet) octahedral and tetrahedral iron sites were identified in the samples. Quantitative analysis was performed for all of the iron sites. We have observed large differences between the Fe²⁺/Fe³⁺ ratio in samples originated from 120–150 km deepness, which phlogopites having been existed at different erosion circumstances. We have found a significantly higher Fe²⁺/Fe³⁺ ratio in phlogopites which had been solidified in 120–150 km depth from the surface of Earth 70–100 million years ago, than those had been crystallized in 60–80 km deepness.     

Mössbauer study of Brazilian soapstone

Steatite mineral rocks, soapstone, have been studied by X-ray diffraction, optical microscopic analysis (modal analysis), electron probe micro analysis and Mössbauer spectroscopy for characterization, mineral percentages and chemical composition. Mössbauer spectra show both, magnetic interactions corresponding to magnetite and doublets corresponding to talc. chlorite, dolomite and tremolite. The temperature dependence of the quadrupole splitting in dolomite has been explained in terms of crystal field interaction.     

Mössbauer study of the effect of rare earth substitution into montmorillonite

Novel montmorillonites were prepared by the exchange of the interlayer cations with a series of rare earth cations (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, and Er) and characterized by XRD, XRF, SEM, chemical analysis and ⁵⁷Fe Mössbauer spectroscopy. An unexpected magnetically split component, assigned to iron being in the interlayer space, was observed in the Mössbauer spectra at 78K in some rare earth cation exchanged montmorillonite. This paper is the initial report about this observation. The transition of iron from the octahedral site to the interlayer and possible incorporation of rare earths in sites different from those which are in the interlayer space was concluded.     

A Mössbauer effect study of barium ferrite ball-milled in air

The effects of dry-milling BaFe₁₂O₁₉ in air for periods of 190, 360, 590, 690 and 1000 h have been investigated by X-ray diffraction and Mössbauer effect measurements. The sizes of the BaFe₁₂O₁₉ particles decrease on milling, as expected, although a partial decomposition of BaFe₁₂O₁₉ to -Fe₂O₃ is found to take place on extended milling (1000 h). The room temperature Mössbauer spectra are consistent with superparamagnetic relaxation associated with the fine BaFe₁₂O₁₉ and -Fe₂O₃ particles. The X-ray diffraction patterns of all the milled samples exhibit features indicative of a disordered structural state, consistent with the nanoscale particles and a nanostructured state.     

Mössbauer effect study of iron decahydrodecaborate chelates containing ferrocenyl group

⁵⁷Fe Mössbauer parameters of three chelates containing ferrocenyl group have been extracted over a temperature range from 12 K to 300 K. In comparison with ferrocene itself it is found that the substituents attached to the cyclopentadienyl ring by -bonding can give an appreciable effect on bonding of central iron atom.Work supported by the Chinese National Science Foundation.     

Mössbauer effect study of the magnetic structure in δ-FeOOH

Two samples of-FeOOH with different particle sizes have been studied in an external field of 4 T and as a function of temperature. They were found to have a ferrimagnetic structure due to an unequal occupancy of antiferromagnetically coupled octahedral ferric ions. The large surface contribution, which is characterized by a canted spin structure and by highly deformed Fe³⁺ co-ordinations, strongly influences the magnetic properties observed with Mössbauer spectroscopy.     

New applications of the Mössbauer effect

Results from a Mössbauer experiment to observe acoustic oscillations induced by pulsed laser excitation in MgO:⁵⁷Fe²⁺ crystal are presented. Time-domain spectra are satsifacorily described by the theory of the frequency modulation of Mössbauer radiation transmitted through a vibrating resonance medium. It is proposed that the D _4Ω/D _2Ω ratio of the fourth and second Fourier harmonics of the modulated radiation be used to measure the amplitude of nuclear oscillations.     

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.     

Mössbauer effect in proteins

In proteins, the M?ssbauer effect and neutron scattering show a broad line and a rapid increase of the conformational mean-square displacement above about 180?K. The increase, dubbed the "dynamical transition," is controversial. We introduce a new interpretation of the M?ssbauer effect in proteins and demonstrate that no dynamical transition is required. The increase in the mean-square displacement and the broad line are caused by fluctuations in the protein's hydration shell. Using the dielectric spectrum of these fluctuations, we predict the shape of the M?ssbauer spectrum from 80 to 295?K with one dimensionless coefficient.     

Mössbauer study of iron-doped lithium niobate

From Mössbauer spectra of LiNbO₃⁵⁷Fe(III) single crystals under external fields of 4.92 and 6.2 T, the crystal field and hyperfine parameters are determined. Transmission integral fits indicate a Boltzmann population of the Fe(III) electronic levels with a spin temperature equal to the sample temperature. Spectra at external fields of 0 T and 19 mT can be satisfactorily simulated using an effective spin 1/2,g-factors calculated from spin-expectation values and an internal averaged dipole field of 5.5 mT inclined 20 to thec-axis. The simulations indicate cross-relaxation between Nb and Li nuclear spins and the Fe(III) electronic spin.     

Mössbauer study of the annealing effect on low‐alloyed steels

Structural analyses of Fe-Cr and Fe-Cr-Ni low‐alloyed steels before and after annealing at 600^○C using Mössbauer spectrometry, X‐ray diffraction and scanning electron microscopy are reported. At the received state, the two steels present a fine bainitic microstructure with equal hardness. From Mössbauer analysis, two iron sites are identified as substitutional by Cr, Mo, Ni atoms and as insertional by carbon in bainitic ferrite. Both sites are locally deformed by residual stresses. The presence of small quantities of retained austenite and ε carbide has been observed. Annealing for one hour at 600^○C causes a decrease in hardness for both steels with a decrease of retained austenite. After longer time of annealing, precipitation of (Fe,Ni)₂₃C₆ occurs in the Fe-Cr-Ni steel and increases hardness.