Fe/Dy artificial multilayered films studied by57Fe Mössbauer spectroscopy

Magnetic properties of multilayered Fe/Dy films with artificial superstructures have been investigated by⁵⁷Fe Mössbauer spectroscopy. Doublet peaks are observed at room temperature when the Fe layer is thinner than 20Å. Mössbauer spectra for thicker Fe layers correspond to α-Fe spectra. In certain samples, i.e. [Fe(44Å)/Dy(6Å)], a gradual spin reorientation takes place, which is evidenced from the change of relative intensities of Δm=0 lines with decreasing temperature.     

Weathering of Martian and Earth surface studied by Mössbauer spectroscopy

Martian regolith and Earth’s basaltoid samples have been investigated by means of Mössbauer spectroscopy. The identification of the same minerals: olivine, pyroxene, magnetite, hematite and confrontation of the Fe^3?+?/Fe^2?+?, Fe^3?+?/Fe_tot, Fe^2?+?/Fe_tot ratios are presented. Co-existence of olivine and hematite in Martian regolith, absent in presented by authors terrestrial samples has been tentatively explained.     

Iron-metal multilayers studied by Mössbauer spectroscopy,RBS and X-ray diffraction

Fe/M (M = Ag, Zn and Sn) multilayers prepared by a vacuum evaporation method are studied by Mössbauer spectroscopy (MS), Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). For the case of an M = Ag multilayer, MS reveals that Fe in the multilayer remains as an-phase down to the layer thickness of 10 nm. This result is in agreement with the RBS result that Fe and Ag form a completely discrete layer structure without any mutual mixing. For the case of M = Zn and Sn, RBS reveals that a considerable mixing has taken place between Fe and Sn during the specimen preparation. MS on Fe/Sn specimens with different layer thickness shows that an alloy phase of about 5 nm thickness is formed at the interface. Structural as well as magnetic properties of the alloy phase are discussed based on MS at different temperatures and on reported results of the intermetallic compound FeSn.     

Mössbauer study of CO-precipitated Fischer-Tropsch iron catalysts

Mössbauer spectroscopy studies of precipitated Fischer-Tropsch (FT) iron catalysts, viz. 100 Fe/5 Cu/4.2 K/x SiO₂, wherex=0,8, 16, 24, 25, 40, or 100, have shown that reduction of the oxide precursor in CO gives rise to -carbide Fe₅C₂ whose amount decreases with an increase of SiO₂ content. The -carbide is converted into magnetite Fe₃O₄ while catalyzing the FT synthesis reaction. A correlation between FT activity and the content of -carbide in the catalysts was found, which indicated that -carbide is active for FT synthesis reaction.     

Magnetism of ErAgSn studied by 119Sn Mössbauer spectroscopy

Antiferromagnetic ErAgSn compound was investigated in detail by ¹¹⁹Sn Mössbauer spectroscopy in a temperature range between 2.2 and 300 K. The ¹¹⁹Sn spectra recorded below 4.2 K can be well fitted with a single main magnetic component in agreement with recent neutron diffraction studies [1]. A broad distribution of magnetic hyperfine fields observed above 4.2 K and enhanced spin correlations among Er³⁺ ions at T > T _N = 5.6 K are the remarkable features of the investigated system.     

Local order of icosahedral quasicrystals studied by Mössbauer spectroscopy

Thermodynamically stable Al-Cu-Fe and Fe-doped ferromagnetic Al-Cu-Ge-Mn icosahedral quasicrystals are studied by⁵⁷Fe transmission Mössbauer spectroscopy and X-ray diffraction experiments. Al₆₅Cu₂₀Fe₁₅ quasicrystalline alloy was subjected to a mechanical grinding (MG) for up to 800 hours in a ball mill. Presence of the amorphous phase which co-exists with the quasicrystalline one is revealed in the early stage of MG. Mössbauer measurements were performed on icosahedral Al₄₀Cu_10–x Ge₂₅Mn₂₅Fe _x quasicrystal (x0.1; 3) in a temperature range from 10 K to 548 K. It was found that a magnetic transition occurs at about 30 K which is far belowT _c reported in the literature. It is concluded that AlGeMn ferromagnet which is present in the samples does not affect the magnetic transition observed and the transition is an intrinsic property of the Al-Cu-Ge-Mn host alloy.Samples of icosahedral quasicrystals were kindly provided by Profs. A. Inoue, T. Masumoto and P. H. Shingu. Ball milling was performed in Kyoto University by a courtesy of Prof. P. H. Shingu. This work was supported by the project for priority areas on properties of quasicrystals (No. 01630003) from the Japanese Ministry of Education, Science and Culture.     

Fast relaxation of polycrystalline Fe(III) complexes studied by Mössbauer spectroscopy

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.     

Atomic short-range order in Fe1−xCrx alloys studied by 57Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for iron-based solid solutions Fe_1?xCr_x with x in the range of 0.01≤x≤0.10. Analysis of the obtained spectra gave clear evidence that the distribution of impurity atoms in the first coordination spheres of ⁵⁷Fe nuclei is not homogeneous and it cannot be described in terms of binomial distribution. Quantitatively, the effects were described in terms of the short-range order parameters.     

Hydrogenation of FeCoZr–Al2O3 nanocomposites studied by Mössbauer spectroscopy and magnetometry

Hydrogenation effects on crystalline and magnetic structure of nanocomposites (FeCoZr) _x (Al₂O₃)_100???x , 38?≤?x?≤?63 at.% are studied by ⁵⁷Fe Mössbauer spectroscopy and magnetometry. Variations of local structure, blocking temperature and mean FeCoZr nanoparticles’ volume are discussed with respect to (i) composition and (ii) two competing processes—H₂ incorporation and annealing—occurred during treatment in H₂ plasma.     

Dynamics of iron in Fe-porphyrin aggregates studied by X-ray absorption and Mössbauer spectroscopy

The iron-porphyrin aggregates were studied by optical absorption and fluorescence method, infrared spectroscopy, X-ray absorption and Mössbauer spectroscopy. The aggregation of porphyrin molecules strengthens the Fe-ligands bonds and accelerates the spin-spin relaxations. A significant speeding-up of relaxation was observed with lowering the temperature down to 25 K. The comparison of the EXAFS (Extended X-ray Absorption Fine Structure) and Mössbauer spectroscopy results enabled some separation of the individual Fe vibration from its collective movement with ligands.     

Crystal field effects in Tm2M17 compounds studied by 169Tm Mössbauer spectroscopy

¹⁶⁹Tm Mössbauer spectra of the compounds Tm₂Fe₁₇ and Tm₂Co₁₇ were measured at various temperatures between 4.2 and 300 K. The spectra were analysed in terms of crystal fields and exchange fields and the presence of two crystallographically nonequivalent Tm sites in these compounds. The crystal field parameters derived from this analysis were used to derive approximate values of the anisotropy constants of these materials.     

Magnetism of (Fe0.93Ni0.07)2P studied using 57Fe Mössbauer spectroscopy

⁵⁷Fe Mössbauer spectroscopic measurements have been carried out on (Fe_0.93Ni_0.07)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.     

193Ir and 57Fe Mössbauer characterisation of iridium/iron bimetallic catalysts for methanol synthesis

Fe-Ir/MgO catalysts derived from the [Et₄N]₂[Fe₂Ir₂(CO)₁₂] cluster precursor, which exhibit a high activity in the synthesis of methanol from CO and H₂, were studied by ¹⁹³Ir and ⁵⁷Fe Mössbauer spectroscopy. The study extends from the precursors via the fresh to the aged catalysts. The presence of iridium in the metallic state as well as the presence of trivalent, divalent and alloyed iron is detected. The different structural features of catalysts prepared from mixed-metal cluster compounds and from inorganic salt precursors are discussed.     

Amorphous magnetic state established by Mössbauer spectroscopy on powders obtained by borohydride reduction

The Mössbauer spectra of a series of iron-cobalt-boron powders with different boron contents are discussed in association with the conditions of borohydride reduction. The most important structural peculiarities due to the composition and the amorphous-crystalline state of the powders are established on the basis of the hyperfine field distribution.     

Electronic property of SrFe2As2 under high pressure studied by 57Fe M?ssbauer spectroscopy

An illustrious complex [Fe(ptz)₆](BF₄)₂ (ptz = 1-propyl-tetrazole) (1) which was produced in the form of submicron crystals and thin film on Allium cepa membrane was probed by ⁵⁷Fe Mossbauer spectroscopy in order to follow its intrinsic spin crossover. In addition to a weak signal that corresponds to neat SCO compound significant amount of other iron compounds are found that could have morphed from 1 due to specific host-guest interaction on the lipid-bilayer of bio-membrane. Further complimentary information about biogenic role of membrane, was obtained from variable temperature Mossbauer spectroscopy on a ~5% enriched [⁵⁷Fe(H₂O)₆](BF₄)₂ salt on this membrane.     

Crystal-chemistry aspects and electric-field-gradient (EFG) dispersion in Ca-gallogermanate-type structures studied by Mössbauer spectroscopy

The crystal field disorder in some trigonal germanates of the type X_3-yLn_yFe_2+yGe_4-yO₁₄ (X = Ba, Sr; Ln = La, Nd; y = 0, 1) is studied by ⁵⁷Fe M?ssbauer effect. The dispersion of the electric field gradient (EFG) at the octahedral sites of these compounds is investigated. A correlation of the experimental and calculated EFG data with some crystal-chemistry aspects is presented. Received 3 February 1999     

Effect of pseudohalides in pentadentate-iron(III) complexes studied by DFT and Mössbauer spectroscopy

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 [Fe^IIIL⁵NCY] complexes.     

Lithium insertion–deinsertion mechanism in NbSn2 anode studied by 119Sn Mössbauer spectroscopy

This article deals with the study of the electrochemical performances and the lithium insertion-deinsertion mechanism by mean of ¹¹⁹Sn Mössbauer spectroscopy of NbSn₂. The first discharge shows a plateau at 0.05 V vs. Li^?+?/Li⁰ corresponding to a displacement reaction with the formation of Li₇Sn₂. A specific capacity of 487 mAh/g can be reached during this first discharge.