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1.
Polycrystalline strontium iron germanates of the type Sr3–y
Ln
y
Fe2+y
Ge4–y
O14(Ln=La, Nd;y=0, 1) were investigated by57Fe Mössbauer spectroscopy in the temperature range 4.2–300 K. The crystal chemistry and the distribution of Fe3+ ions in the structure, as well as the crystallographic inequivalence of the oxygen polyhedra occupied by iron, were studied over the whole paramagnetic temperature region. A correlation of the experimental data with a local environment computation is given. 相似文献
2.
3.
Ce20Fe80 ribbons have been produced by planar flow casting under an He atmosphere at linear wheel velocities between 19 and 29 m s–1. Analysis of ribbons by X-ray diffraction and57Fe Mössbauer spectrometry in the temperature range 77–300 K shows that the ribbons are crystallized. For higher velocities, the ribbon is constituted of the two equilibrium phases CeFe2 and Ce2Fe17, but, for lower velocities, there appears a third iron metallic phase, which can be explained by the quenching rate of the melt. A coherent hyperfine parameter set was deduced from fitting Mössbauer spectra in the whole temperature range. 相似文献
4.
57Fe Mössbauer spectra of Invar type (Fe.65Ni.35)1–xMnx alloys (O相似文献
5.
M. Pissas V. Psycharis D. Stamopoulos G. Papavassiliou Y. Sanakis A. Simopoulos 《Solid State Communications》2006,137(12):668-672
We studied by Mössbauer spectroscopy the Na0.82CoO2 compound using 1% 57Fe as a local probe which substitutes for the Co ions. Mössbauer spectra at T=300 K revealed two sites which correspond to Fe3+ and Fe4+. The existence of two distinct values of the quadrupole splitting instead of a continuous distribution should be related with the charge ordering of Co+3, Co+4 ions and ion ordering of Na(1) and Na(2). Below T=10 K part of the spectrum area, corresponding to Fe4+ and all of Fe3+, displays broad magnetically split spectra arising either from short-range magnetic correlations or from slow electronic spin relaxation. 相似文献
6.
(Ce0.2Fe0.8)1-x
Al
x
(0 x 0.9) ribbons have been prepared by planar flow casting under an He atmosphere with a linear velocity of 29 m s-1. Analyses of the ribbons by X-ray diffraction and57Fe Mössbauer spectrometry in the temperature range 4–300 K show that all the ribbons are crystalline. With increasingx, the observed phases are Ce(Fe, Al)2, Ce2(Fe, Al)17, CeFe4+y,Al8-y and the single fcc aluminium phase. For the different phases, the line intensities of the Mössbauer spectra agree with previous results on the preferential substitution sites for aluminium. A coherent hyperfine parameters set was deduced from fitting spectra in the temperature range 4–300 K. 相似文献
7.
Tris complex of FeII2(2′-pyridyl)imidazole has been encapsulated in the supercages of zeolite Y and characterized by using powder XRD, FTIR, Mössbauer spectroscopy, variable temperature magnetization and MAS NMR techniques and results have been compared with those obtained for this complex with ClO4− and SO42− as anions. At room temperature, the [Fe(pyim)3](ClO4)2 complex exhibited low spin state, while [FeII(pyim)3]SO4 exhibited the existence of both low and high spin states. The encapsulated [FeII(pyim)3]2+ complex exhibited a broad quadrupole doublet characterized by isomer shift, δ=+0.55 mm/s and quadrupole splitting ΔEq=1.26 mm/s. The magnetization measurements carried out for the encapsulated [FeII(pyim)3]2+ complex showed a systematic decrease in its values with decreasing temperature down to 75 K with no indication of thermal hysteresis effects. These results suggest the existence of a dynamic spin state equilibrium between the high and low spin states for the encapsulated [FeII(pyim)3]2+ complex with time constant comparable to the characteristic Mössbauer time scale of 57Fe nuclei. 相似文献
8.
The Mössbauer effect spectra of structurally characterized molecular metal clusters provide a valuable reference point for the identification of surface generated species important in chemisorption and catalysis. The resulting hyperfine parameters may also aid structural elucidation and provide insight into the electronic environment of the individual iron sites. We have studied in detail the clusters Na2Cu6Fe4(CO)16, Na3Cu5Fe4(CO)16, and Na3Cu3Fe3(CO)12, and several related compounds. The results indicate that the Mössbauer effect isomer shifts at 78K, which vary from –0.123 to –0.035mm/s, are very sensitive to the bonding in the molecular cluster. 相似文献
9.
Nanoparticles of zinc substituted Mg-ferrite with compositions Mg(1-x)Zn
x
Fe2O4 (x = 0.15, 0.30 and 0.50) having particle sizes in the range 6.4 nm to 21.4 nm prepared by the co-precipitation method were characterized by 57Fe Mössbauer spectroscopy, X-ray diffratometry and AC magnetic susceptibility measurements. Mössbauer measurements at room temperature and down to 20 K clearly indicate presence of superparamagnetic particles in all the samples. AC magnetic susceptibility data show lowering of blocking temperature with decrease of particle size. Superparamagnetic relaxation was observed for larger particle size in samples with higher Zn content, which is attributed to the weakening of A-B exchange interaction in ferrite lattice due to replacement of Fe3 + in tetrahedral site by Zn2 + ions.Received: 16 April 2004, Published online: 23 July 2004PACS:
75.50.Tt Fine-particle systems; nanocrystalline materials - 76.80. + y Mössbauer effect; other gamma-ray spectroscopy - 75.30.Cr Saturation moments and magnetic susceptibilitiesS. Das: Present address: Department of Physics, Jadavpur University, Kolkata - 700032, India 相似文献
10.
The Mössbauer effect has been studied in the mixed ferrites Co
x
Fe3–x
O4 (forx=0.8, 0.9 and 1) with the spinel structure in the temperature range between 78 and 380 K. The composition withx=1, showed an expected Zeeman spectrum with two overlapping magnetic hyperfine patterns related to the Fe3+ ions in tetrahedral and octahedral sites. While for samples withx=0.8 and 0.9 the Mössbauer spectrum for each compound was successfully analysed into three different patterns corresponding to the ferric ions placed at the tetrahedral and octahedral sites and ferrous ions at the octahedral sites, indicating no electron transfer between Fe3+ and Fe2+, where the quantity of cobalt is sufficiently large to be located at the six nearest neighbours to ferrous ions. The Mössbauer effect parameters were calculated for these observed sites and their variation with temperature reported. The reduced hyperfine magnetic fields of the Fe3+ (B) ions were found to follow the Brillouin curve forS=5/2 and one third power law. The magnetic ordering temperature was determined to be 815 K and the possible magnetic interactions were discussed. 相似文献
11.
Charge disproportionation in La0.5Ca0.5FeO3−δ perovskite has been detected by zero-field Mössbauer spectra from 20 K to room temperature. On the basis of the parameters of center shifts and hyperfine fields, Mössbauer spectra identified that the iron ionic states are Fe3+ and Fe5+ below 150 K, Fe3+, Fe4+ and Fe5+ in the intermediate temperature region, as well as Fe3+ and Fe4+ above 220 K. At low temperatures, the system exhibits a cluster-glass-like state resulting from competition between antiferromagnetic interaction of Fe3+–Fe3+ and ferromagnetic interaction of Fe3+–Fe5+. 相似文献
12.
K. E. R. England C. M. B. Henderson J. Charnock D. J. Vaughan 《Hyperfine Interactions》1994,91(1):709-714
Synthetic iron-containing leucite-type phases have been studied using57Fe Mössbauer spectroscopy in combination with X-ray absorption spectroscopy (XAFS and XANES). The Mössbauer and XAS data confirm that both Fe2+ and Fe3+ occupy tetrahedrally coordinated framework sites in the synthetic phases. In addition, information on Fe2+/Fe3+ ratios, cation site occupancies and first shell bond lengths has also been obtained. 相似文献
13.
J. R. Regnard R. Guillen A. Wiedenmann G. Fillion S. Hafner K. Langer 《Hyperfine Interactions》1986,28(1-4):589-592
Magnetic properties of orthoferrosilite FeSiO3 have been examined using susceptibility, magnetization measurements and Mössbauer spectroscopy. From magnetic and Mössbauer measurements, one obtains close values of the magnetic ordering temperature, TN=39±1 K and TN=41±1 K, respectively. The magnetic order is characterized by strong ferromagnetic coupling of Fe2+ moments within the ribbons and a weak antiferromagnetic coupling of the moments between adjacent ribbons. The 4.2 K Mössbauer spectra can be fitted with two different hyperfine magnetic fields Hhf=68 kOe and Hhf=314 kOe which can be assigned to Fe2+ in the octahedrally coordinated M1 and M2 sites, respectively, of the FeSiO3 structure. 相似文献
14.
Complete replacement of copper by iron in RBa2Cu3O7 leads to RBa2Fe3O8 (R=Y, rare earth). Mössbauer spectroscopy measurements of57Fe and151Eu in RBa2Fe3O8 (R=Y, Eu, Ho, Er) at temperatures 4.2–800 K have been performed. Some of the spectra reveal two inequivalent iron sites, probably corresponding to iron in the Fe(2) site (fivefold oxygen coordination) and in the Fe(1) site (octahedral oxygen coordination). In all compounds the iron moments order antiferromagnetically at the same Néel temperatureT
N720 K. The151Eu Mössbauer spectra of EuBa2Fe3O8 show that the Eu ion is trivalent and exposed to a small exchange field from the iron sublattices. 相似文献
15.
M. Lengen E. Bill C. Butzlaff A. X. Trautwein M. Winter P. Chaudhuri 《Hyperfine Interactions》1994,94(1):1849-1853
The magnetic properties of [L-Fe(III)-dmg3Mn(II)-Fe(III)-L] (ClO4)2 have been characterized by magnetic susceptibility, EPR, and Mössbauer studies. L represents 1,4,7-trimethyl-, 1,4,7-triazacyclononane and dmg represents dimethylglyoxime. X-ray diffraction measurements yield that the arrangement of the three metal centers is strictly linear with atomic distancesd
Fe-Mn=0.35 nm andd
Fe-Fe=0.7 nm. Magnetic susceptibility measurements (3–295 K) were analyzed in the framework of the spin-Hamiltonian formalism considering Heisenberg exchange and Zeeman interaction:=J
Fe-Mn(S
Fe1+S
Fe2)S
Mn +J
Fe-Fe(S
Fe1
S
Fe2) +gB
S
total
B. The spinsS
Fe1=S
Fe2 =S
Mn=5/2 of the complex are antiferromagnetically coupled, yielding a total spin ofS
total=5/2 with exchange coupling constantsF
Fe-Mn=13.4 cm–1 andJ
Fe-Fe= 4.5 cm–1. Magnetically split Mössbauer spectra were recorded at 1.5 K under various applied fields (20 mT, 170 mT, 4T). The spin-Hamiltonian analysis of these spectra yields isotropic magnetic hyperfine coupling withA
total/(g
N
N)=–18.5 T. The corresponding local componentA
Fe is related toA
total via spin-projection:A
total=(6/7)AFe. The resultingA
Fe/(g
NN)=–21.6 T is in agreement with standard values of ferric high-spin complexes. Spin-Hamiltonian parameters as obtained from Mössbauer studies and exchange coupling constants as derived from susceptibility measurements are corroborated by temperature-dependent EPR studies. 相似文献
16.
Spectrometric studies were carried out on samples of tourmaline (schörl-dravite series) from geological environments where first-phase-formed tourmaline underwent influence of geochemically different fluids. Samples are from a differentiated magmatic complex of Trento-Alto Adige, Italy, and from hydrothermal gold and silver deposits of the Humboldt Range, Nevada, USA. Chemical data were obtained from electron microprobes. The results of Mössbauer measurements suggest three to five doublets. Fe occurs in two valence states. The Z-site, usually fulfilled with Al3+ and Fe3+, is assigned only to Al3+ and Fe2+. This location was found in nearly all samples studied. In the Y-site Fe2+ and Fe3+ are obviously present. Isomer shifts with intermediate values can be assumed to be related to intervalence charge transfer (IVCT). Optical spectroscopy reveals absorption bands at 9 000 and 14000 cm–1, which are assigned to a charge transfer between Fe2+ and Fe3+, the 23 000 cm–1 absorption band is supposed to be due to Fe2+ Ti4+ charge transfer. The occupation of the Z-site only by Fe2+ and the coexistence of divalent and trivalent Fe in the Y-site could be explained by selective oxidation in Y-site through a late process. 相似文献
17.
Zhiguo Liu Dawei Dong Milan Liu Yu Sui Wenhui Su Zhengnan Qian Zhe Li 《Hyperfine Interactions》2005,163(1-4):13-27
The quadrupole splitting distributions (QSDs) from the Mössbauer spectra of triphylite, ferrisicklerite and purpurite at 298 K and 80 K were obtained by the use of the Voigt-based quadrupole splitting distribution (QSD) method for the first time. QSDs of Fe2+ and Fe3+ are attributed to Fe2+ and Fe3+ at the corresponding octahedrally coordinated sites in the crystal structures of the three phosphate minerals. The influence on the distortion of the M2 site by different next-nearest neighbor (NNN) configurations was discussed based on the Jahn–Teller effect in purpurite, and the authors propose two M2 subsites with different distortions in purpurite. Two QSDs of Fe3+ in the Mössbauer spectra of purpurite are tentatively assigned to Fe3+ at the two M2 subsites, and next-nearest neighbor (NNN) effects were used to interpret the Mössbauer spectra of purpurite. 相似文献
18.
J. Maknani J. L. Dormann V. G. Terziev J. Jové H. Pankowska O. Gorochov R. Suryanarayanan 《Hyperfine Interactions》1994,93(1):1699-1703
YBa2(Cu1–x
Fe
x
)3O7–d
annealed in an Ar atmosphere, then reoxygenated at various temperatures, has been studied by Mössbauer spectroscopy at 300 K and low temperature with and without an applied field of 5.5 T. The results are interpreted as being due to Fe clustering remaining in the chains rather than a significant transfer to the planes. 相似文献
19.
S. J. Stewart G. F. Goya R. C. Mercader A. E. Goeta G. Punte F. Sapinya-Navarro 《Hyperfine Interactions》1994,83(1):419-424
The structural and magnetic properties of iron-doped Gd2BaCuO5 have been studied by X-ray diffractometry, Mössbauer spectroscopy and susceptibility measurements. Mössbauer data on Gd2BaCu0.8Fe0.2O5 show that at room temperature Fe is not magnetically ordered, displaying hyperfine parameters similar to those generally assigned to Fe at Cu(2) sites in the GdBa2(Cu1–x
Fe
x
)3O7 superconductor. Susceptibility measurements demonstrate that Gd2BaCu1–x
Fe
x
O5 behaves like a three-dimensional antiferromagnet withT
N=11.9±0.1 K, independent ofx. The effective magnetic moment calculated within a mean field approximation is consistent with an ordering of the Gd sublattice. 相似文献
20.
The57Fe Mössbauer spectroscopy of amorphous Fe90–xCoxZr10 and Fe90–xNixZr10 provided strong evidence for the unusual large enhancement of the Fe magnetic moment in these alloys. 相似文献