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1.
Mössbauer spectra of polycrystalline samples of Fe(Ox)3, Fe(BPHA)3 and K3[Fe(malonate)3] · 3H2O exhibit fast relaxation patterns in the temperature range 4.2–300 K. The magnetic hyperfine splitting has nearly completely collapsed due to rapid electronic spin-spin relaxation of the Fe ions. We use a static Hamiltonian and describe the spin-spin interaction by an effective field Hamiltonian . From this the relaxation supermatrix and the Mössbauer spectra are calculated. The random texture of the samples is taken into account by averaging the radiation dipole operators over the whole sphere. Least-squares fits of the spectra for longitudinal, isotropic and transverse spin relaxation are presented. From the fits the temperature dependence of the relaxation is obtained. We conclude that in these materials the iron is present as high-spin Fe(III) and that the crystal field splitting constantD is greater than zero. The sign ofV zz is found to be positive.  相似文献   

2.
3.
The states of iron and europium in the EuO:Fe composite spintronic material have been studied by means of room-temperature Mössbauer spectroscopy. In both cases, two sets of lines indicating the ferromagnetism and superparamagnetism of metallic iron nanoparticles in the composite and the appearance of a fraction of europium ions in the Eu3+ oxidation state in the matrix in addition to the main Eu2+ state have been observed in the respective spectra. In the europium case, the observation implies the possibility of a partial spin polarization of paramagnetic europium ions in Eu-Fe-O clusters and an increased specific magnetization of the composite.  相似文献   

4.
Mössbauer absorbtion spectra of57Fe-doped NaCl crystal were measured and correlated with an adequate electric field gradient computation to describe the dipolar complexes occuring at the decay of Suzuki-phase under thermal treatment and X-ray irradiation. An electrostatic potential of the type was taken into account in the evaluation of EFG tensor.  相似文献   

5.
The structure of LiNbO3-type FeTiO3 and the oxidation state of Fe have been investigated using X-ray diffraction and Mössbauer spectroscopy in the diamond anvil cell up to 18 GPa at room temperature. A structural phase transition is observed at 15.7 GPa from LiNbO3-type to perovskite-type, accompanied by a volume collapse of 1.5%. LiNbO3-type FeTiO3, which is shown to contain only ferrous iron up to this pressure, and no charge transfer is observed. In addition to the c/a axial ratio that has been used to distinguish between ilmenite and LiNbO3-type FeTiO3, the hyperfine parameters (isomer shift and quadrupole splitting) provide an efficient way to discriminate between these two phases.  相似文献   

6.
Mössbauer investigations of zirconium alloys were examined. Data about the chemical state of iron atoms in the zirconium alloys of different composition has been provided. Mössbauer spectroscopy revealed that small quantities of iron in binary zirconium alloy are in the solid solution α-Zr (up to 0.02 wt.%). Different iron atoms concentration and thermo-mechanical treatments may lead to formation the intermetallic compounds Zr3Fe, Zr2Fe, ZrFe2. Adding tin atoms does not affect the formation and shape of Mössbauer spectra of these compounds. Adding Cr and Nb atoms makes significant changes in the shape of Mössbauer spectra and leads to the formation of complex intermetallic compounds. Adding Cu and W atoms, the shape of the binary alloys spectra (Zr-Fe) remains unchanged, but a change in the temperature dependence behavior of the spectral parameters occurs and also, changes to the properties of the alloys.  相似文献   

7.
In order to investigate the electronic state, the local structure, and the magnetic structure of a new ion oxide Fe3B7O13(OH), we have applied 57Fe Mössbauer spectroscopy. The room-temperature values of isomer shift and quadrupole splitting are 1.16 mm/s and 3.21 mm/s, respectively, which indicate that the Fe ions are in high spin Fe2?+? state. The spectrum at 4.2 K is composed of a well-resolved hyperfine sextet with the hyperfine field of 3.6 T. In a trimer, each Fe2?+? magnetic moment is supposed to be directed from Fe2?+? to OH???.  相似文献   

8.
Trivalent iron sulfide (Fe2 S 3) particles were synthesized using a modified polyol method. These particles exhibited a needle-like shape (diameter =?10-50 nm, length =?350-1000 nm) and generated a clear XRD pattern. Mössbauer spectra of the product showed a paramagnetic doublet at room temperature and distributed hyperfine magnetic splitting at low temperature. The Curie temperature of this material was determined to be approximately 60 K. The data suggest that the Fe2 S 3 had a structure similar to that of maghemite (γ-Fe2 O 3) with a lattice constant of a =?10.6 Å. The XRD pattern calculated from this structure was in agreement with the experimental pattern and the calculated hyperfine magnetic field was also equivalent to that observed in the experimental Mössbauer spectrum.  相似文献   

9.
57Fe Mössbauer spectroscopic measurements have been carried out on (Fe0.93Ni0.07)2P in the temperature range 85–405 K. Obtained values of hyperfine field at the two metallic sites are slightly smaller than in Fe2P. But the reduction is much less than as reported in Cr or Mn or Co substituted analogues of Fe2P.  相似文献   

10.
A Mössbauer spectroscopy study was made on Ho3Fe5-xAlxO12 (x=0.0, 0.05, 0.7). X‐ray diffraction patterns indicate that the samples with x=0.0 and 0.05 have the garnet structure, while the sample with x=0.7 has an additional noncubic structural phase. The room temperature spectrum for samples with x=0.0 and 0.05 consists of two magnetic components corresponding to the octahedral and tetrahedral sites with hyperfine magnetic fields (Bhf) of 50 T and 40 T, respectively. For x=0.7 we observe a new magnetic component with Bhf= 45 T, a reduction in the intensity and broadening of the tetrahedral component, and the evolution of a nonmagnetic central component. These variations are evidently due to the addition of aluminium to the system. At liquid nitrogen temperature the samples with x=0.0 and 0.05 are nearly identical. It was also observed that the increase in Bhf for the octahedral site is smaller than that for the tetrahedral site as the temperature is lowered to 80 K.  相似文献   

11.
The microscopic models which are commonly used to interpret the temperature variations of the centre shifts and quadrupole splittings observed from the Mössbauer spectra of iron-containing minerals are briefly presented and illustrated using the results of recent studies of ortho- and clinopyroxenes. The importance of applied-field Mössbauer spectroscopy for the determination of the electric field gradient is indicated. Aspects of the magnetic spectra of Fe2+-bearing minerals emphasise the benefit of using external fields to elucidate the nature of the magnetic ordering. Two Fe3+ minerals, bernalite and franklinite, serve as examples to illustrate this point. Finally, two applications of the Mössbauer milliprobe technique are presented: the characterisation of inclusions in diamond, and the determination of the oxidation state of a new iron uranyl sulfate mineral, deliensite.  相似文献   

12.
The setting up and updating of a Mössbauer laboratory imply the acquisition and assembling of different units. Guidelines concerning either the construction or the acquisition of the various parts which compose a Mössbauer spectrometer are given in this paper.  相似文献   

13.
Mononuclear iron complexes in which the iron(III) ion is coordinated by a pentadentate Schiff base ligand L5 with two phenolate, two imino and one amino group can exhibit a spin crossover. In this contribution experimental results are presented for complexes with cyanate and thiocyanate as co-ligands. Furthermore, theoretical results of quantum chemical calculations of energies and entropies for the low-spin and high-spin state are shown and compared with Mössbauer results. We also demonstrate how the ligand field of the monodentate co-ligand influences the spin crossover energies and entropies in [FeIIIL5NCY] complexes.  相似文献   

14.
We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe3?+? in MgO single crystals, obtained after implantation of 57Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, τ ???1 as a parameter. The temperature dependent spin relaxation rate of Fe3?+? in MgO is found to increase to ~108 s???1 at 647 K by assuming a relaxation rate of τ ???1?< 106 s???1 at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe3?+? from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides.  相似文献   

15.
In this paper, we briefly summarize the main conclusions of the Mössbauer analysis of [L2Fe2(-OH)3] (ClO4)2·2CH3OH·2H2O with L=N,N',N"-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which possesses a central exchange-coupled delocalized-valence Fe(II/III) unit. The complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. The magnetic Mössbauer spectra imply a system spinS t=9/2 for the dimer in its ground state. The values for hyperfine and spin-Hamiltonian parameters, obtained from simulations of the Mössbauer spectra, are =0.74 mms–1, E Q=–2.14 mms–1,A =–10.6 T,A =–13.5 T andD=1.8 cm–1. The system spinS t=9/2 is interpreted to be a consequence of double-exchange coupling.  相似文献   

16.
We have previously reported the stability of europium oxalate compared to ammonium europium bis-salen and europium benzoate. We now extend the dicoarboxylic acid chain of the oxalate by introducing additional-CH2-groups in the dicarboxylate ligands by using malonate, succinate, glutarate and adipate. Additionally, we have examined the effect of alterations in the succinate dianion by introducing functional groups such as [C = C]in the case of the maleide and-OH group in the case of the malide. This study is an attempt to further characterize these compounds. Infrared spectra were used to characterize bridging and chelating dicarboxylates while Mössbauer spectroscopy measurements were used to gain better insight into the structure of heterocyclic “cages” containing two Eu3?+? ions and two dianions.  相似文献   

17.
Nano scale magnetite based ferrofluid is synthesized by chemical co pre cipitation technique and stabilized with oleic acid. Magnetization and viscosity measurements were used to optimize for texturing purpose. The freeze-textured ferrofluid in two configurations, namely, (1) field texture system (FTS) and (2) zero field texture system (ZTS) are investigated by magnetization measurements at 298 K and Mössbauer spectroscopy measurements at 77 and 298 K. These results are analysed on the basis of the contributions from collective superparamagnetic reversal and the strength of the inter particle interactions.  相似文献   

18.
The contribution of Mössbauer spectroscopy to the study of conventional superconducting materials, Chevrel phases, rare earth rhodium borides, high Tc cuprates, and Ru-based superconducting-magnetic systems are very shortly reviewed. The newly discovered oxypnictides, magnetic and superconducting (mostly the Fe–As) systems, are discussed in great detail.  相似文献   

19.
Photosynthesis is a process occurring in certain species of bacteria, algae and higher plants. It transforms solar energy into various forms of energy-rich organic molecules. Photosystem II (PSII) is the “heart” of the photosynthetic apparatus because it delivers electrons and protons for further steps of the light-driven phases of photosynthesis. There are two enigmatic iron binding structures within the core of photosynthetic apparatus, which play an important role in the electron transfer within PSII. Many investigations focus on the determination of their function which is the key to the understanding of the molecular mechanism of the energy and electron transfer within PSII. Among many methods used in this research field, the Mössbauer spectroscopy is a unique one, which gives the possibility to study changes of the valence and spin states of those two iron sites and the dynamical properties of their protein matrix in the presence of various physiological and stress conditions.  相似文献   

20.
W. Potzel 《Hyperfine Interactions》1992,71(1-4):1515-1522
The 93.31-keV Mössbauer resonance in67Zn is used to determine tiny changes of the transition energy. We first report on a gravitational redshift (GRS) experiment with67GaZnO single crystal source and67ZnO powder as absorber. The results on the GRS show that solid state effects which are difficult to control experimentally, in particular the extreme sensitivity of the electric field gradient tensor (efg) in67ZnO to small external pressure, finally limit the accuracy in determining the GRS. The resonance has been further employed to investigate solid state properties of67ZnO with high precision. At large pressures67ZnO exhibits a phase transition from hep (wurtzite) to fcc (NaCl) structure. The changes of the efg and of the s-electron density θ(0) at the67Zn nucleus with reduced unit cell volume show that covalency of the Zn-O bond plays and essential role. We have performed self-consistent Hartree-Pock cluster calculations to describe the experimental changes of θ(0) in detail.  相似文献   

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