Paramagnetic Peak Research Articles

Mössbauer spectrometric study of Sm2Fe17Nx (x=0–8)

Ternary rare-earth-iron-nitrogen compounds of Sm2Fe17Nx with x ranging from 0 up to 8, which have a rhombohedral structure of Th2Zn17 and a high Curie temperature up to 475–480°C depending on the degree of nitrogenation, were prepared by the nitrogenation of arc-melted Sm2Fe17 in mixed ammonia and hydrogen gas atmospheres of various ratios, and Mossbauer spectra of these compounds were observed at room temperature in order to analyse the physicochemical state of the nitrogenated products. The obtained data were analysed by focusing main attention on the effect of degree of nitrogenation on the variation of spectral profiles. Paramagnetic peaks due to an amorphous compound became prevalent as x became higher than ~ 2.3.

Mössbauer study of the firing process of the imitative ancient sky-blue Jun porcelain

Mossbauer spectra of the imitative ancient Jun porcelain indicate that the glaze and body materials contain Fe2O3, Fe3O4 and structural iron. It is clear that during the firing process, the glaze undergoes dehydration, dehydroxylation, vitrification and recrystallization. The Fe2+ quadrupole splitting value of the paramagnetic peak of the body material is high even at low firing temperatures. For the body material, the distinction between dehydration and dehydroxylation is not clear. The changes of magnetism of the glaze and body materials in the firing process and the coloring mechanism of the sky-blue Jun porcelain are analyzed in the present paper.

Structural analysis of the myoglobin reconstituted with iron porphine.

Sperm whale apomyoglobin was complexed with iron porphine to examine the influence of completely removed heme side chains on the entire molecular structure. Paramagnetic NMR peak from the proximal histidine of the deoxy protein ensured formation of the iron-histidine bond. Porphine pyrrole-proton NMR signals of the cyanmet and deoxy derivatives are unusually sharp single lines manifesting rapid heme rotation about the iron-histidine bond. X-ray crystallographic structure of the cyanmet derivative, determined with a final R factor of 0.21 for 11,808 independent reflections ranging from 7 to 1.8 A, was resolved at 1.8 A resolution. The result confirmed 1:1 coupling between apomyoglobin and iron porphine. The cyano ligand adopts a bent configuration with an Fe-C-N angle of 127 degrees and a Fe-CN distance of 1.89 A. The overall globin structure and side chain conformations are remarkably similar to those of native myoglobin despite intensive disruption of the original heme-globin interactions. The native apoprotein structure unexpectedly conserved even after iron porphine insertion demonstrates that the complex polypeptide fold of holomyoglobin is more inherent in the amino acid sequence than is generally believed.

2相ステンレス鋳鋼におけるフェライトの相分離過程のメスバウアー分光測定

Duplex stainless steels become brittle at medium temperatures, owing to the phase decomposition of a ferrite into a Cr-rich α′ phase and an Fe-rich α phase. A cast CF3M duplex stainless steel containing 25% volume fraction of ferrite was aged at 723 K for time periods up to 10000 h to investigate the phase decomposition mechanism and to evaluate the composition of the decomposition products using Mössbauer spectroscopy at room temperature. The half width of the internal magnetic field distribution curve estimated from the experimental Mössbauer spectra increases in the initial stage of aging, suggesting compositional fluctuation due to spinodal decomposition. The ferrite phase finally decomposes into the Fe-rich α and Cr-rich α′ phases after prolonged aging. The composition of the Fe-rich α phase is estimated to be Fe-11 at%Cr-5 at%Ni by numerically analyzing the internal magnetic field distribution based upon the local environmental effect of solute atoms on the central Fe nucleus. The result is consistent with the one previously obtained by atom-probe analysis. The isomer shift of 57Fe in the α′ phase is estimated to be −0.114±0.002 mm/s at room temperature by decomposing an overlapped paramagnetic absorption peak into component peaks. The Cr content of the phase is estimated to be about 85 at% by plotting the isomer shift on an experimental isomer shift versus Cr content diagram.

Hyperfine-field studies of Fe3Al and Fe3-xCrxAl alloys.

Measurements of hyperfine fields have been performed on ordered and disordered ${\mathrm{Fe}}_{3}$Al alloys and disordered ${\mathrm{Fe}}_{3\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cr}}_{\mathit{x}}$Al alloys for 0\ensuremath{\le}x\ensuremath{\le}1 with use of a $^{57}\mathrm{Fe}$ M\"ossbauer technique. The Curie temperatures of all the samples were measured with use of the zero-velocity thermal-scan method. The Curie temperature decreases linearly with increasing chromium concentration. M\"ossbauer spectra of the samples show the presence of a paramagnetic peak coexisting with the hyperfine structure for x\ensuremath{\ge}0.5. The spectra fitted with a hyperfine-field distribution show the presence of two hyperfine-field components. The lower of these in disordered ${\mathrm{Fe}}_{3}$Al is assigned to have 5 nearest-neighbor Al atoms and the higher-field one to have 2--3 nearest-neighbor Al atoms. A systematic replacement of Fe with Cr shows a linear decrease with increasing Cr concentration for both field components. The change in the lower field is only 65 kOe while that in the higher one is 120 kOe over the entire Cr-concentration range. The rapid decrease in the high-field component with increasing Cr concentration points to the fact that despite the considerable disorder which exists, Cr preferentially substitutes for iron at sites having 2--3 nearest-neighbor Al atoms.

Mössbauer spectrometric study of Sm 2Fe 17N x ( x = 0 ∼ 8)

Ternary rare earth-iron-nitrogen compounds, Sm 2Fe 17N x , prepared by the nitridation of arc melt Sm 2Fe 17 in mixed gas atmospheres of ammonia and hydrogen of various ratios, have a rhombohedral structure of Th 2Zn 17 and a high Curie temperature up to 560°C depending on the degree of nitridation. The Mössbauer spectra of Sm 2Fe 17N x ( x = 0–8) compounds were observed at room temperature and analysed focussing main attention to the effect of nitrogen on the variation of spectral profiles. New paramagnetic peaks due to amorphous compound appeared in the sample with higher x than ∼ 2.3.

メスバウアー分光法によるFe-28Cr-5Ni合金中の2相分離相の組成決定

The effect of Ni on the internal magnetic field and the isomer shift of 57Fe in Fe-Cr alloys containing 3 to 14 at%Cr and 70 to 90 at%Cr were examined at room temperature by Mössbauer spectroscopy. A model Fe-28%Cr-5%Ni alloy was aged up to 5000 h at 723 K to investigate the phase decomposition of ferrite in a commercial duplex stainless steel. The alloy finally decomposed into a Cr-rich phase (α′) and an Fe-rich phase (α) after aging. A paramagnetic absorption peak due to the α′ phase has an isomer shift of −0.110 mm/s at room temperature. The value corresponds to a Cr content of 85(±1)at%Cr. The composition of the α phase was estimated to be 11(±1)at%Cr from the average internal magnetic field and the internal field distribution curve. The result of α phase was consistent with a result obtained by atom probe microanalysis. The latter underestimated the Cr content of the α′ phase in comparison with the Mössbauer effect.

Local Structure, Tg, and IR Transparency of Potassium Titanate Glasses and the Local Structure of Calcium Titanate Ceramics

Abstract The Mössbauer spectrum of xK2O·(95−x)TiO2·5Fe2O3 glasses (x=35–60), consisting of a paramagnetic doublet peak due to tetrahedral Fe3+, suggests that the Fe3+ is substituted for the tetrahedral Ti4+. The isomer shift (δ=0.20–0.23 mm s−1) and the quadrupole splitting (Δ=0.72–0.81 mm s−1) decrease linearly with the increasing K2O content. The glass transition temperature (Tg) decreases similarly as the Δ does, supporting the “Tg−Δ rule” discovered by Nishida et al., i.e., the Tg of oxide glasses is expressed by Tg=aΔ+b. (The slope “a” is 680 °C mm−1 s.) The IR absorption spectra show two peaks at 880 and 640 cm−1 corresponding to the Ti(Fe)O4 and TiO6 units, respectively. The relative absorption intensity of the Ti(Fe)O4 units becomes higher when the K2O content increases. The potassium titanate glasses (plate) show IR transparency, having the transmission edge of 5.4 μm. The Mössbauer spectrum of xCaO·(95−x)TiO2·5Fe2O3 ceramics (x=5–50) consists of two doublet peaks due to Fe3+ and Fe2+. Both the δ and Δ of the Fe3+ are constant irrespective of the CaO content, whereas the fraction (relative absorption area) of the Fe3+ decreases linearly from 94 to 75% when the CaO content is increased from 5 to 50 mol%.

A Study on Magnetic Properties of Fe4N Powders

Magnetization and Mössbauer spectra were measured for three kinds of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N powders made from acicular α-FeOOH, α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and carbonyl iron powders. Except for the Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N powder from carbonyl iron, the saturation magnetization was lower than the bulk value (190 emu/g). A large amount of oxygen and small amounts of Ni, Zn and Si were detected in the sample obtained from α-FeOOH. From the Mössbauer spectra, it was concluded that decreases in the saturation magnetization were mainly due to the coexistence of a paramagnetic phase. A large quadrupole splitting of the paramagnetic peak indicates that the paramagnetic phase may be an oxide consisting of Fe(II) ions, e.g. wustite. In addition, it is thought that Ni and Zn preferentially substitute for Fe at the corner sites of fcc Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N, and also reduce the magnetization.

Ｆｅ４Ｎ微粒子の磁気特性に関する一考察

Magnetization and Mossbauer spectra were measured for three kinds of Fe4N powders made from acicular α-FeOOH, α-Fe2O3 and carbonyl iron powders. Except for the Fe4N powder from carbonyl iron, the saturation magnetization was lower than the bulk value (190 emu/g). A large amount of oxygen and a small amount of Ni, Zn and Si were detected in the sample from α-FeOOH. According to the Mossbauer spectra, it was concluded that the decreases in the saturation magnetization were mainly due to the coexistence of a paramagnetic phase. A large quadrupole splitting of the paramagnetic peak indicates that the paramagnetic phase may be an oxide consisting of Fe(II) ion, e. g., wustite. In addition, it is considered that Ni and Zn preferentially substitute Fe at the corner of fcc-Fe4N and also reduce the magnetization.

Neutron scattering measurements of critical exponents inCsMnBr3: AZ2≥1antiferromagnet

CsMnBr/sub 3/ is an XY-like antiferromagnet on a stacked, triangular lattice with nearest-neighbor interactions. It orders antiferromagnetically at T/sub N/ = 8.3 K. We have used neutron scattering measurements of the frequency-integrated critical scattering in the paramagnetic state and magnetic Bragg peak intensity in the ordered state to determine the critical exponents ..gamma.., ..nu.., and ..beta... Based on these measurements we conclude that ..gamma.. = 1.01 +- 0.08, ..nu.. = 0.54 +- 0.03, and ..beta.. = 0.21 +- 0.02. These values do not correspond to any standard universality class characterized by the dimensionality of the lattice and the order parameter. They do, however, agree with predictions by Kawamura for a universality class characterized by the symmetry of the order parameter, Z/sub 2/ x S/sub 1/. This symmetry differs from that of the standard XY model (S/sub 1/) due to the presence of chiral degeneracy (Z/sub 2/), a consequence of lattice frustration.

Structural Study of Na2O–TeO2 Glasses by Mössbauer Spectroscopy and Differential Thermal Analysis

Abstract A Mössbauer spectrum of xNa2O·(95−x)TeO2·5Fe2O3 glasses (0≤x≤35) consists of a paramagnetic quadrupole doublet peak with an isomer shift of 0.39±0.01 mm s−1 with respect to metallic iron. Quadrupole splitting of the doublet peak changes gradually from 0.76 to 0.60 mm s−1 when Na2O content is changed from 0 to 35 mol% at 5 mol% intervals. These results suggest that Fe3+ ions are present at substitutional sites of Te4+ ions constituting distorted TeO4 trigonal bipyramids. Each of the distorted TeO4 trigonal bipyramids has an oxygen vacancy and a lone electron pair at one of the equatorial sites. Decreased quadrupole splitting is ascribed to an increased symmetry of FeO4 (and also TeO4) trigonal bipyramids, due to a formation of nonbridging oxygen atoms followed by a gradual change of the glass matrix from a two-(β-TeO2) or three-(α-TeO2) dimensional network structure to a lower dimensional network structure. These structural changes are also deduced from a composition dependency of glass transition temperatures (Tg), which decrease continuously from 318 to 232 °C with increasing Na2O content.

Magnetic and crystallographic characterization of Zn0.78Fe0.22Se and FeSe films on GaAs (001)

We have grown single-crystal (001) epilayers of the diluted magnetic semiconductor Zn1−xFexSe with 0≤x≤1 on GaAs(001) substrates by molecular-beam epitaxy. The films retain the zinc-blende structure for thicknesses up to at least 2 μm for x≤0.22, while epilayers with higher Fe concentrations can be stabilized up to some decreasing critical thickness. SQUID magnetometry data obtained for x=0.22 indicate Van Vleck paramagnetic behavior accompanied by a decrease in the fraction of magnetically free Fe2+ ions with increasing x. Conversion electron Mössbauer spectra of the FeSe epilayers show a dominant paramagnetic central peak at both 300 and 13.5 K, with small contributions from Zeeman-split components at low temperature. The samples were further characterized with x-ray rocking curve, θ-2θ, and topography measurements.

The influence of Cr content in Fe-Cr-Co alloys on the magnetic properties and Mössbauer effect

Fe-xCr-8Co (x=24, 25, 27, 29 and 32 wt%) permanent magnetic alloys have been studied bv Mossbauer effect, magnetic balance and vibrating-sample magnetometer. It is indicated that the optimum permanent magnetic properties obtained for the composition of the alloys at about x=27. The value of Cr content in these alloys sigificantly influences the average hyperfine field, the saturation magnetic moment, the proportion of paramagnetic phase and orientation of magnetic moment in these alloys. The intrinsic coercive force is gradually reduced with the temperature decreasing from 290 to 77k. The paramagnetic peak in the spectrum disappars at about 125k. The certain mechanism has been suggested to explain the experimental results.

ＦｅＯｘ‐ＣａＯ‐ＳｉＯ２三元系アモルファス酸化物の磁性と磁気構造

The amorphous phase region is located in a narrow area near the side of CaO-SiO2. The magnetization of amorphous oxides is very small at the room temperature, but markedly increases for temperatures lower than about 50 K. The room temperature Mossbauer spectra indicate paramagnetic peaks. The spectra at 77K reveal six weak Zeeman peaks buried in the background. At 4.2 K, a well resolved hyperfine sextet is observed. The Mossbauer results suggest that the Fe atoms are distributed inhomogeneously in the solid and that the structural short-range order around Fe atoms is very strong, having random bonding and distance fluctuation.

Stage dependence of magnetic susceptibility of intercalated graphite

The orbital magnetic susceptibility of two coupled graphite layers is calculated as a function of temperature and Fermi energy ($\ensuremath{\mu}$). The susceptibility is shown to be diamagnetic at small values of $\ensuremath{\mu}$, and paramagnetic at large values of $\ensuremath{\mu}$, with a paramagnetic peak at $\ensuremath{\mu}\ensuremath{\cong}{\ensuremath{\gamma}}_{1}$, where ${\ensuremath{\gamma}}_{1}$ is the interlayer coupling. These results explain the increase in the susceptibility as a function of stage which has recently been observed in ${\mathrm{KC}}_{12n}$.

Mössbauer effect study of ‘475°c embrittlement’ of duplex and ferritic stainless steels

The phenomenon of ‘475°C embrittlement’ of a duplex stainless steel and seven single phase ferritic alloys was studied with Mössbauer spectroscopy and transmission electron microscopy. The alloys studied included two binary Fe-Cr alloys and multicomponent alloys containing Ni, Mo and Cu as well as Fe and Cr. There is a hyperfine field shift with aging at 475°C in all of the alloys. In addition, paramagnetic peaks and precipitates are observed only in the alloys containing Ni. These results are described in terms of Cr and Fe separation via spinodal decomposition. Furthermore, in the Ni containing alloys, the peak local Cr level is estimated as being higher than 78 at.% whereas in the Ni free alloys, after similar heat treatments, the peak local Cr level is estimated as being only about 45 at%.