Mössbauer effect studies of amorphous metals in magnetic radiofrequency fields

The effects are described of magnetic radiofrequency (rf) field-induced modulation of Mössbauer radiation (rf sidebands) and of the fast relaxation of the magnetic hyperfine field due to the rf field (rf collapse). The coexistence and separation of these effects is discussed. The rf collapse of the magnetic hyperfine structure which allows direct observation of the quadrupole interaction in the ferromagnetic state provides the method for studying the shortrange order in amorphous metals. Examples of FeSiB, FeNiSiB, FeCoSiB, and FeB are discussed with reference to structural models. The effect of rfenhanced crystallization of amorphous metals and its relation to the rf sideband effect is reported. It is shown that by Mössbauer spectroscopy it is possible to follow the kinetics of rf crystallization and to identify the phases formed in various amorphous metals due to rf-induced crystallization.     

Mössbauer study and magnetic properties of M-type barium hexaferrite doped with Co + Ti and Bi + Ti ions

Using X-ray powder diffractions, M?ssbauer spectroscopy, and magnetic measurements, the effect of complex dopants (Co2+ + Ti4+) and (Bi3+ + Ti4+) on the fine structure and magnetic properties of M-type barium hexaferrite prepared by hydroxide and carbonate precipitations has been studied. The distribution of cations over five nonequivalent positions of barium hexaferrite with magnetoplumbite structure is discussed. It has been shown that doped barium hexaferrite can be used for high-coercitivity data storage media.     

57Fe Mössbauer spectroscopy on multiwalled carbon nanotubes with metal filling

M?ssbauer measurements at different temperatures are reported for MWCNTs with metallic encapsulations ("nanowires"). The spectra can reasonably be refined with two subpatterns: one providing clear evidence of an iron carbide Fe(3)C (cementite) phase as the main nanowire component and the other yielding a relaxation doublet most probably belonging to the same phase. Whereas the former one displays a well resolved magnetic hyperfine spectrum with Brillouin type temperature dependence, the latter one gains importance with rising temperature or onset of an inhomogeneous external magnetic field. The comparably large incoherent scattering is attributed to the graphene layers of the tube walls. The experimental results are discussed on the background of an interpretation model trying to explain unusual magnetometric results published elsewhere.     

Investigation on the magnetic and Mössbauer spectroscopy of 57Fe doped LiMnPO4

Journal of Radioanalytical and Nuclear Chemistry - The 57Fe doped LiMnPO4 cathode with potential applications in Li-ion batteries was prepared by solid-state reaction. The magnetic susceptibility...     

Mössbauer study of some Fe-containing M6 and M5 clusters

Isomer shift (δ) and quadrupole splitting (Δ) parameters have been assigned to the iron sites in [FeRh₅(CO)₁₆]⁻, trans- and cis-[Fe₂Rh₄(CO)₁₆]²⁻, [Fe₃-Rh₃(CO)₁₇]³⁻, [FeRh₄(CO)₁₅]²⁻, [Fe₃Pt₃(CO)₁₅]²⁻ and [Fe₄M(CO)₁₆]²⁻ (M = Pd or Pt) from ⁵⁷Fe Mössbauer spectra recorded at 78 K. The data for the closo compounds [FeRh₅(CO)₁₆]⁻ and [Fe₂Rh₄(CO)₁₆]²⁻ are compared with those for [Fe₆(CO)₁₆C]²⁻. In [Fe₃Rh₃(CO)₁₇]³⁻, the three major Fe sites were identified. For both [Fe₄M(CO)₁₆]²⁻ compounds two isomers were shown to be present in the solid state.     

Mössbauer study of iron-containing atmospheric aerosols

The Mössbauer technique was applied to study the seasonal variations of iron concentration in atmospheric air. The concentration of iron in air was calculated by the area method from the experimental spectra obtained. From the shapes of the Mössbauer spectra it was concluded that iron appears as Fe₂O₃ in the form of ultrafine particles in the superparamagnetic state. The measurements as a function of temperature [from 300 to 75 K) made it possible to estimate the size of iron-containing aerosol particles. Correlation of the seasonal variations of iron concentration with meteorite activity was discussed. This method was applied also in investigations of iron concentration variations with air radioactivity due to nuclear explosions performed in the atmosphere. Attempts were made to find a relation between air pollution and the concentration of iron in the air.     

Formation and tribological properties of composite Langmuir–Blodgett films of stearic acid with molybdenum disulfide and amorphous carbon

The morphology and tribological properties of Langmuir–Blodgett mono- and bilayers of stearic acid with particles of molybdenum disulfide (MoS₂) and amorphous carbon (С), prepared on silicon and steel substrates by horizontal deposition (stearic acid–MoS₂ and stearic acid–С monolayers) and by the “roll” technique (stearic acid–MoS₂/stearic acid–С bilayers), were studied. Incorporation of C and MoS₂ particles into the structure of a stearic acid film enhances its wear resistance by a factor of 2.8 and 5.5, respectively. The presence of MoS₂ and С particles and of their aggregates of size from ~220 nm to 16.3 μm in stearic acid layers was confirmed by atomic force microscopy.     

Magnetic and Mössbauer effect study of YTi(Fe1−xNix)11

The magnetic properties and ⁵⁷Fe Mössbauer spectra of the compounds YTi(Fe_1−xNi_x)₁₁ were investigated. The compounds crystallize in a ThMn₁₂-type structure when x < 0.7. The substitution of nickel for iron results in an increase in Curie temperature with x < 0.5, and a peak is observed in the composition dependance of saturation magnetization at x = 0.07. The Mössbauer effect measurements were carried out at room temperature with x equal to 0.00, 0.04, 0.08 and 0.20. The best fits indicate that nickel atoms preferentially occupy the j and f sites. A maximum was found in the variation of hyperfine field as a function of nickel content, which is in good agreement with the results of magnetic measurements.     

The role of alpha-iron and cementite phases in the growing mechanism of carbon nanotubes: a 57Fe Mössbauer spectroscopy study

57Fe M?ssbauer spectroscopy was used to study the reduction behavior at temperatures as high as 1073 K of an iron/silica catalyst, and also the carbonaceous materials isolated after acetylene decomposition over this catalyst at several temperatures (873-1073 K). The products were previously characterized by transmission electron microscopy and it was clearly proven that the concentration of carbon nanotubes increased when reaction reached highest temperatures. This was related with an increment in cementite concentration (generated from initial alpha-iron and the progressive reduction of the remnant Fe+2 caused by acetylene decomposition) as detected by 57Fe M?ssbauer. These results undoubtedly revealed the role of alpha-iron as active center for acetylene decomposition and cementite as main carbide intermediate species in the catalytic growth of CNTs.     

Mössbauer effect study on dispersion and annealing behaviour of Fe(III) ions coprecipitated with neodymium trihydroxide

Mössbauer resonance examination at 300 and 77 K of Fe(III) ions 5 weight percent coprecipitated with neodyminum trihydroxide and heated for 24 hr at 100, 350, 600, 725 and 825°C is reported. To investigate the nature of thermal and microstructural processes which occur during phase transitions, samples annealed at different temperatures from 100 to 1200°C were also studied using thermal analysis, IR spectroscopy, electron microscopy and powder X-ray diffraction. Iron ions exist as very fine ferric oxide hydrate gel like species in the coprecipitate. Removal of water in early stages at 100°C results in strengthening of iron ions while in samples annealed at 350°C a particular loosening of iron sites is observed accompanying disruption of lattice planes due to pronounced dehydroxylation. Annealing to 600°C results in precipitation of NdFeO₃ like microphases in CNd₂O₃ lattice. For samples annealed at 725°C C→ANd₂O₃ transformation takes place and the Mössbauer spectra show a quadrupole split doublet resulting from dispersion of iron microphases. Annealing to 825°C, crystallization to hexagonal ANd₂O₃ takes place. Iron ions held still in defect correlated lattice sites exhibit magnetic ordering due to pronounced agglomeration of NdFeO₃ microphases in ANd₂O₃.     

Synthesis and magnetic properties of an iminonitroxide-substituted phenolate–Cu complex

A new spin-chelate, iminonitroxide-substituted phenolate–copper complex (1), was designed and prepared. The structure of the complex 1 was considerably deviated from a square-planar geometry. The dihedral angle between the two planes defined by a set of copper, oxygen and nitrogen atoms was about 41°. The complex was found to have a relatively strong ferromagnetic interaction and a weaker antiferromagnetic interaction: J/k_B=+250 K and θ=−17 K using a three-spin model. The ferromagnetic interaction was assigned to the intramolecular interaction between the copper atom and the iminonitroxide. The antiferromagnetic interaction was assigned as an intermolecular interaction. These assignments were supported by susceptibility measurements for the diluted sample in polyvinyl chloride (PVC) film. The antiferromagnetic interaction was tentatively assigned due to the observed short intermolecular contacts between the C5 and O1 atoms or between the H5 and O1 atoms.     

Mössbauer study of Japanese ancient iron slag

Mössbauer spectroscopy was applied to an investigation of ancient iron slags, excavated at the ancient ruins for iron manufacturing in order to deduce the raw materials and operative conditions of the furnace. From the Mössbauer spectra, it was found that the slags consisted of fayalite, wüstite, ulvöspinel and magnetite.     

Phenazineoxonium chloranilatomanganate and chloranilatoferrate: synthesis,structure, magnetic properties,and Mössbauer spectra

Russian Chemical Bulletin - Crystalline compounds (H3O)2(phz)3M2(C6O4Cl2)3·(CH3COCH3) n ·(H2O) n (n = 0?2, M = Mn (1), Fe (3)) were obtained in an acetone-water-tetrahydrofuran...     

The effect of Nb and Ni addition on crystallization behavior of amorphous–nanocrystalline Fe–Cr–B–Si alloys

The crystallization behavior of amorphous Fe–Cr–B–Si alloys in the presence of Ni and Nb elements was the goal of this study. In this regard, four different amorphous–nanocrystalline Fe₄₀Cr₂₀Si₁₅B₁₅M₁₀ (M=Fe, Nb, Ni, Ni_0.5Nb_0.5) alloys were prepared using mechanical alloying technique up to 20 h. Based on the achieved results, in contrast to Fe₅₀Cr₂₀Si₁₅B₁₅ alloy, the amorphous phase can be successfully prepared in the presence of Ni and Nb in composition. Although the crystallization mechanism of prepared amorphous phase in different alloys was the same, the Fe₄₀Cr₂₀Si₁₅B₁₅Nb₁₀ alloy showed higher thermal stability in comparison with other samples. The crystallization activation energy of this amorphous alloy was estimated about 410 kJ mol^?1 which was much higher than Fe₄₀Cr₂₀Si₁₅B₁₅Ni₁₀ (195.5 kJ mol^?1) and Fe₄₀Cr₂₀Si₁₅B₁₅Ni₅Nb₅ (360 kJ mol^?1) samples. The calculated values of Avrami exponent (1.5 < n < 2.2) indicated that the crystallization process in different alloying systems is the same and to be governed by a three-dimensional diffusion-controlled growth.     

57Fe Mössbauer spectroscopic and magnetic study of a spin-crossover polymer complex, Fe(3-chloropyridine)2Ni(CN)4

The coordination polymer Fe(3-chloropyridine)₂Ni(CN)₄ (2) has been prepared by a method similar to that for Fe(pyridine)₂Ni(CN)₄ (1). The complex (2) has been characterized by⁵⁷Fe Mössbauer spectroscopy and a SQUID technique.⁵⁷Fe Mössbauer and magnetic susceptibility data show that complex (2) exhibits spin-crossover behavior. The spin transition of (2) occurs between 120 and 80 K with very small hysteresis or without hysteresis. The temperature range of the spin transition in (2) is lower than that in (1). A residual high spin iron(II) fraction is observed at low temperatures in (2), being different from (1). SQUID data also show that samples treated differently yield different spin transition curves.     

Variable-temperature 119Sn Mössbauer study of tin phthalocyanines

Variable-temperature ¹¹⁹Sn Mössbauer spectroscopic (VTMS) data for six tin phthalocyanine (pc) derivatives have been collected in order to ascertain the restrictions imposed by the macrocyclic ring on the vibrational motion of the tin atom. Thermal condensation of [(t-Bu)₄pc]Sn(OH)₂ yields the co-facially stacked polymer {[(t-Bu)₄pc]SnO}_n which can be distinguished in the VTMS experiment by the enhanced rigidity of its structure.     

A study of XeFeF9 from Mössbauer spectra

A study of the new antiferromagnetic complex XeFeF₉ by the Mössbauer effect has contributed experimental data on the temperature dependence of hyperfine splitting parameters of ⁵⁷Fe. There is evidence that the relative intensity of the lines is affected by the texture. The anomalous spectra in the range 85 – 100 K might be interpreted as superparamagnetism; the corresponding blocking temperature being obtained near 98 K.     

A study of carbonic anhydrase using Mössbauer spectroscopy

The preparation and characterization of an Fe(II) bovine carbonic and human carbonic anhydrase are presented. Results of Mössbauer spectroscopy measurements indicate that the Fe(II) (low spin) is bound at the enzymatically active site. The results are compared with previous studies which had used the technique of perturbed angular correlations of γ-radiation.