A Mössbauer spectroscopic study of the magnetocrystalline anisotropy inα-FeOOH

Mössbauer spectra are obtained for a single crystal of -FeOOH, with a magnetic field of up to 10T applied along the c axis. No spin reorientation is observed, indicating a lower limit of 6 × 10⁴ J/m³ for the anisotropy constant K. A theoretical estimate gives K > 1.1 × 10⁶ J/m³.     

A Mössbauer spectroscopic study of cobalt-iron molybdates

Fe _x Co_1–x MoO₄ compounds prepared by coprecipitation were studied by XRD, electrical conductivity and mainly by absorption and emission Mössbauer spectroscopy. FeMoO₄ and CoMoO₄ samples were shown to contain Fe³⁺ and Co³⁺, respectively, in solid solution. Three kinds of Fe _x Co_1–x MoO₄ solids can be described. Forx0.16: one has a -Co(Fe²⁺, Fe³⁺)MoO₄ solid solution. For 0.17x0.25: one has the same solid solution with its surface rich in Fe³⁺. Forx0.26: one has the same solid solution with only bulk Fe³⁺, and ferric molybdate. Studies of reduction by hydrogen and of catalytic reaction of mechanical mixtures of CoMoO₄ and ferric molybdate support these statements.     

M?ssbauer spectroscopic study of spin reorientation in Mn-substituted yttrium orthoferrite

The first-order spin-reorientation transition in the Mn-substituted yttrium orthoferrites, YFe(1-x)Mn(x)O(3) (x = 0.1, 0.15 and 0.2), has been investigated using (57)Fe M?ssbauer spectroscopy. Owing to its large anisotropy, substitution of Mn(3+) ions in YFeO(3) induces a spin-reorientation transition from the low-temperature antiferromagnetic state to a high-temperature weak ferromagnetic state. With increasing x, the spin-reorientation transition temperature (T(SR)) increases whereas the Néel temperature (T(N)) decreases. Analysis of the M?ssbauer spectra unambiguously confirms the occurrence of spin reorientation relative to crystal axes. At a given temperature, the mean hyperfine field decreases with the increasing Mn concentration. The variation of canting angle with temperature for YFe(0.85)Mn(0.15)O(3) has been estimated.     

A Mössbauer spectroscopic study of the effect of molybdenum during preparation of Nd-Fe-B magnets

Elements in atomic ratios Nd₂(Fe_0.9Mo_0.1)₁₄B were melted in an induction furnace and annealed in order to examine the effect of molybdenum during the preparation of Nd-Fe-B magnets. A phase analysis has been made from ⁵⁷ Fe Mössbauer spectroscopic measurements in the temperature range of 100 to 700 K. It is found that two iron containing phases are formed, one Mo rich Fe alloy and the other Nd-Fe(Mo)-B isostructural to Nd₂Fe₁₄B. The Nd_1.1Fe₄B₄ phase usually found in Nd-Fe-B magnets is not observed in these samples. The Curie temperature, T_c, is found to be 605(5) K from the Mössbauer as well as vibrational sample magnetometer measurements on the same sample. At low temperatures, the average hyperfine field at Fe nuclei is found to show a decrease with respect to the value for Nd₂Fe₁₄B.     

Gamma-x ray coincidence Mössbauer spectroscopic study of the aftereffects in sulfate hydrates

The anomalous charge states formed after the electron capture decay, of⁵⁷Co in FeSO₄·H₂O and FeSO₄·7H₂O are investigated using the conventional Mössbauer emission spectroscopy and a gamma-X ray coincidence method. This method is based on the idea that a Mössbauer spectrum observed with the coincidence technique only when K-X rays are emitted is reflected by isolated events with a reduced influence of the Auger-electron self-irradiation. The formation of the anomalous electronic and structural configuration is attributed to the self-radiolysis of the H₂O and SO ₄ ^2? ligands in the nearest and the second nearest coordination shells around the decaying atom.     

Mössbauer spectroscopic study of ferrocene derivatives in the adsorption and liquid-crystalline states

Mössbauer spectra of ferrocene derivatives in the solid, adsorption and liquidcrystalline states were measured at temperatures ranging from 78 to 423 K. The peak intensities of the Mössbauer spectra of ferrocene derivatives adsorbed on silica gel decreased markedly with an increase in temperature. The Mössbauer absorption of [4-(4-methoxyphenoxycarbonyl)-phenoxycarbonyl]alkyl 4-ferrocenylbenzoate at 295 K during the cooling process was observed in what was assumed to be the liquid-crystalline state.     

A Mössbauer spectroscopic study of simulated weathering of Didwana ordinary chondrites

A sample of an ordinary chondrite fall, Didwana-Rajod, Rajasthan, India which was shown to be largely unweathered, was exposed to weathering in laboratory conditions. Wet and dry cycle of different strengths (0.01 and 0.1 M) of sodium sulfate solution was applied for different periods of time (maximum of 140 days). An attempt was made to simulate meteorite weathering more or less analogous to environmental exposure in desert-like conditions. It is found that lower concentration of the attacking ions is more effective in weathering the meteorite. Kamacite is affected in early cycles of weathering more than any other mineral. The olivine to pyroxene ratio is much less affected.     

Mössbauer spectroscopic study on chemical changes of iron compounds with the aid of sulfate-reducing bacteria

⁵⁷Fe Mössbauer spectra were measured of reaction products formed during an incubation experiment with sulfate-reducing bacteria, which were isolated from estuarine sediments of the Tama River in Tokyo. The spectrum of the product incubated for several days showed some overlapping sextets. This product had a different chemical form from amorphous iron monosulfide produced by inorganic reaction between ferrous and sulfide ions. It was estimated that the structure of nearest neighbor of iron in this product was similar to that of pyrrhotite (Fe_1?x S). After several months of incubation, other singlet and doublet appeared successively on the spectrum, corresponding to mackinawite (FeS_1?x ) and new sulfide, respectively. Both values of isomer shift and quadrupole splitting of new sulfide increased with increasing incubation time and approached those of pyrite (FeS₂). Extended X-ray absorption fine structure (EXAFS) showed that iron atoms were coordinated by sulfur in the incubation product.     

Feasibility study to investigate diffusion of Fe in Si using a Mössbauer spectroscopic microscope

A prototype Mössbauer Spectroscopic Microscope is applied for the feasibility study of ⁵⁷Fe impurity diffusion in Si wafers. A 2nm- ⁵⁷Fe deposited Si wafer is annealed at 430 °C for 1 hour, and subsequently the 1/3 area of the wafer is further grinded with an angle of 6 degrees to the original surface to get a higher depth resolution for the mapping. Subsequently, the mapping images for Fe\(_{\text {sub}}^{\mathrm {0}}\), Fe\(_{\text {int}}^{\mathrm {0}}\), and Fe\(_{\text {int}}^{\mathrm {+}}\) states are measured separately for the two different areas: one area (A) along the grinded surface, and the other (B) along the original wafer surface crossing through the ⁵⁷Fe-deposition boundary. By integrating the mapping intensity the diffusivity of each Fe component along the two different directions can be evaluated and compared with an average Fe diffusivity in Si, which is measured by EDS mapping data obtained for the same area.     

Mössbauer spectroscopic study of iron fluoride surface layers

The reaction products formed during exposure of iron foils to hydrogen fluoride in the presence of atmospheric oxygen and water have been examined with conversion electron Mössbauer spectroscopy (CEMS) [1]. After exposure for several hours the product in the corrosion layer was found to consist mainly of the mixed-valence iron fluoride, Fe₂F₅·7H₂O. Although the products formed during the initial steps of the reaction could not be completely characterized, a model for the reaction process is suggested.     

A Mössbauer spectral study of the Jilin meteorite

The iron57 Mössbauer spectra of three different samples of the Jilin meteorite have been measured at 78 and 295 K. Five iron containing major components are identified, two magnetic components, kamacite and troilite, and three nonmagnetic components, olivine, pyroxene, and an iron(III) component. The relative absorption areas of these five components show that sample A contains a larger fraction of magnetic components, ca. 50 percent, than samples B and C, which contain ca. 30 percent. This difference indicates a significant compositional inhomogeneity in the Jilin meteorite. The fit of the troilite component sextet is extensively discussed in the paper and requires the adjustment of not only the isomer shift and hyperfine field, but also of the quadrupole interaction, the asymmetry parameter of the electric field gradient tensor, and the orientation of the hyperfine field in the principal axes of the electric field gradient tensor. The smaller isomer shift and hyperfine field of the kamacite mineral in sample B indicate that this sample contains less nickel than the kamacite in samples A and C, in which the amount of nickel is estimated to be ca. 9 percent. On the basis of its hyperfine parameters, the iron(III) component is assigned to iron(III) substituted on the M1 site of pyroxene.     

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.     

Iron-57 Mössbauer spectroscopic study of fluorinated strontium orthoferrite

A nuclear spin maser of a new type, that employs a feedback scheme based on optical nuclear spin detection, has been fabricated. The spin maser is operated at a low static field of 30 mG by using the optical detection method. The frequency stability and precision of the spin maser have been improved by a highly stabilized current source for the static magnetic field. An experimental setup to search for an electric dipole moment (EDM) in ¹²⁹Xe atom is being developed.     

Mössbauer spectroscopic study of 57Fe metabolic transformations in the rhizobacterium Azospirillum brasilense Sp245

Preliminary ⁵⁷Fe transmission Mössbauer spectroscopic data were obtained for the first time for live cells of the plant-growth-promoting rhizobacterium Azospirillum brasilense (wild-type strain Sp245) grown aerobically with ⁵⁷Fe^III–nitrilotriacetate (NTA) complex as a sole source of iron. The results obtained have shown that live cells actively reduce part of the assimilated iron(III) to iron(II), the latter amounting up to 33 % of total cellular iron after 18 h of growth, and 48 % after additional 3 days of storage of the dense wet cell suspension in nutrient-free saline solution in air at room temperature (measured at 80 K). The cellular iron(II) was found to be represented by two quadrupole doublets of different high-spin forms, while the parameters of the cellular iron(III) were close to those typical for bacterioferritins.     

A Mössbauer spectroscopic study of 3d magnetism of R2Fe14B

Guided by the occupancies and iron magnetic moments μ³, ⁵⁷Fe Mössbauer parameters of Y₂Fe₁₄B at 250K, and in turn for other temperatures, of the sublattices of iron were deduced. Plots of μ(T) in reduced coordinates, through the established correlation between hyperfine field Hn and μ, show that the corresponding state of different iron sites is different and all experimental points fall below Brillouin function. The relation between exchange integral deviation parameter Δ and standard deviation of Fe-Fe interatomic distances S is linear, indicating electrostatic nature of exchange interactions between spins in neighboring atoms. It is inclined to the view that fluctuations of exchange integral is responsible for low T_c of R₂Fe₁₄B.     

A M?ssbauer study of the magneto-structural coupling effect in SrFe2As2 and SrFeAsF

In the present paper, we report a comparison study of SrFe₂As₂ and SrFeAsF using M?ssbauer spectroscopy. The temperature dependence of the magnetic hyperfine field is fitted with a modified Bean–Rodbell model. The results give much smaller magnetic moment and magneto-structural coupling effect for SrFeAsF, which may be understood as due to different inter-layer properties of the two compounds.     

Mössbauer spectroscopic studies of ferrocene adsorbed on silica gel

Mössbauer spectra of ferrocene adsorbed on silica gel were measured in order to study the state of adsorption. Ferrocene adsorbed on silica gel tended to oxidize in air and form ferricenium ion. It is assumed that the oxidation of adsorbed ferrocene was caused by surface hydroxyls on the silica gel and O₂ in air. It was observed that ferrocene adsorbed weakly at 293 K, although the ferricenium ion adsorbed strongly at 293 K. Thus the adsorption states of ferrocene depend on the experimental condition.     

A new study on the catalytic mechanism of Fe-based alloys in diamond formation by Mössbauer spectroscopy

M?ssbauer spectroscopy has been used to systemically study the catalytic mechanism of Fe-based alloys in diamond formation at high temperature–high pressure (HTHP) for the first time. M?ssbauer spectra reveal the magnetic state of the 3d electrons of a Fe atom in the Fe-based alloy catalyst during diamond formation at HTHP. During carburization at lower temperatures than that required for diamond formation and diamond formation in the diamond-stability region using Fe-based alloys as a catalyst, both the quadrupole splitting QS and the isomer shift IS change from negative to positive, especially reaching a state in which they are zero. It was indicated that the state of the 3d-shell electrons of the iron atom changes greatly during carburization and diamond formation and that the incomplete 3d sub-bands of Fe atoms in the catalyst alloys could be filled up in proper order by electrons of interstitial carbon atoms. During diamond formation, the unpaired 3d-shell electrons of an iron atom in the Fe-based alloy absorb and interact with 2P_z electrons of the carbon atoms. There exist a Fe–C bonding and an electron charge transfer stage. The 2P_z electrons of the carbon atoms could be dragged into the metal atoms in the catalyst alloy and would make a transition of triangular (sp²π) hybridization of valence electrons to tetrahedral (sp³) hybridization of valence electrons (a transition of sp²π bonds of graphite to sp³ bonds of diamond), resulting in a transition of graphite structure to diamond. Although the conclusion of this study is strictly applicable only to Fe-based alloy catalysts, it could be considered more general because of the chemical similarities between the transition elements used as solvent catalysts for diamond synthesis. Received: 2 March 2001 / Accepted: 20 August 2001 / Published online: 2 October 2001     

Mössbauer spectroscopic study of FeAl1−x Co x

We report the results of a Mössbauer study of the alloy sytem FeAl_1?x Co _x forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN₂ temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field \(\bar B_{hf} \) as a function of temperature is obtained. The variation of \(\bar B_{hf} \) withT is explained using the model of magnetic clusters with collective magnetic excitations from which the saturation hyperfine field and the magnetic anisotropy energy for these clusters are obtained. Also, the results are discussed using the model of random atomic distributions, and the agreement between the calculated and the experimentally obtained distributions of hyperfine fields is found improve asx increases.