Mossbauer Absorption Research Articles

Local Structure and Anti-Structural Defects of Tin in Amorphous and Crystalline Ge2Sb2Te5 Films

The absorption Mossbauer spectroscopy on 119Sn impurity centers shows that germanium atoms in the structure of amorphous and polycrystalline Ge2Sb2Te5 films have different local symmetries (tetrahedral in the amorphous phase and octahedral in the crystalline). By emission Mossbauer spectroscopy on 119mSn impurity centers formed after the radioactive decay of 119Sb or 119mTe parent atoms, tin antisite defects at antimony and tellurium sites of crystalline Ge2Sb2Te5 films are identified.

Fe3 – δO4 Nanoparticles Synthesized in the Presence of Natural Polyelectrolytes

Mossbauer absorption spectroscopy and X-ray diffraction analysis were used to study Fe3 – δO4 nanoparticles formed in the presence of natural polyelectrolytes of two types: derivatives of humic materials and low polymer chitosan. By an example of samples synthesized using either the Massart method or by in situ oxidation of metal it was shown that polyelectrolytes differing in charge and hydrophility affect mainly the morphology of Fe3 – δO4 particles, whereas their composition and structure depend only slightly on the polyelectrolyte nature.

Synchrotron-radiation-based Mössbauer absorption spectroscopy with high resonant energy nuclides

We successfully observed the synchrotron-radiation-based Mossbauer absorption spectra with 158Gd and 99Ru. Their nuclear resonant energies were 79.5 keV and 89.6 keV, respectively, and they are factually the highest energy which energy region synchrotron radiation covers with sufficient intensity as the incident X-rays for Mossbauer spectroscopy. Although the low recoilless fraction owing to these high resonant energy, Mossbauer energy spectra of GdPd3 to 158Gd2O3 and fcc-Ru nanoparticles to bulk hcp-99Ru metal were obtained with natural samples of the former compounds with sufficient amount, because of the high transparency of these high energy X-rays(to electronic scattering). In spite of large statistical errors, we can evaluate the hyperfine parameters when the spectrum includes simple 1-site profile. 99Ru and 158Gd SR-based Mossbauer absorption spectra of various complex materials including somewhat complex structures will be available with the improvements to the measurement system; More detector elements for larger solid angle subtended to the scatterer sample will yields more counting rates and improvement higher recoilless fraction by arranging more appropriate chemical specimen as the scatterer yields deeper absorption profile.

61Ni synchrotron-radiation-based Mössbauer absorption spectroscopy of Ni nanoparticle composites

We obtained energy-domain 61Ni synchrotron-radiation-based Mossbauer absorption spectra of three materials that relate to nanoparticles: Ni2(C8O6H2) metal-organic frameworks (MOFs), Ni nanoparticles synthesized by complete heat decomposition of the MOFs, and the composites of Ni nanoparticles and the MOFs synthesized by partial decomposition of the MOFs. The 61Ni abundance of all the samples was not enriched but we were successfully able to obtain their spectra in 1 day or less, by using a highly efficient measurement system where the internal conversion electrons from energy standard 61Ni86V14 foil were detected. Although both nanoparticle constituent and MOF constituent in the composites included Ni atoms, the Mossbauer parameters of the Ni nanoparticle constituent could be evaluated; the magnetic hyperfine field of the Ni nanoparticle constituent in the composites was different from that of the Ni nanoparticles obtained by the complete heat decomposition. This difference implied that the 3d and/or 4s electron configuration of the nanoparticle constituent were affected by the MOF constituent in the composites.

Mössbauer spectroscopy under acoustical excitation: thick target effects

A new model of Mossbauer absorption (transmission) spectra with an adequate analysis of the possible effects of acoustic excitation in the thick targets is proposed. In particular, the dependence of the line width of acoustical satellites on the degree of phase correlation of the sound oscillations of resonant nuclei in the target is established by calculations and confirmed in experiment. Such a model is stimulated by an increase in the informativeness of the Mossbauer experiments, using thick samples in ultrasound (US) field, and by possible applications of this research technique. The test measurements of Mossbauer absorption spectra on stainless steel are carried out. The fitting of these spectra confirms the relevance of modifications of the model base of Mossbauer processes in US field.

Crystallograhic and magnetic properties of Fe1−x Ni x Ga2O4

We report the crystallographic and magnetic effects on inverse spinel Fe1−xNixGa2O4 (0.0 ≤ x ≤ 0.9) due to doped Ni cations. The crystalline structures of Fe1−xNixGa2O4 (0.0 ≤ x ≤ 0.9) were examined by using a Philips X’Pert diffractometer with a Cu Kα radiation (λ = 1.5406 A) source and analyzed with the Rietveld refinement method. The crystal structures were found to be inverse spinel with space group Fd-3m. From the Rietveld analysis, with increasing Ni concentration, the ratio of magnetic Fe2+ cations, compared to the total number of Fe2+ cations on A-site (tetrahedron) decreased from 43 to 7%, and that on B-site (octahedron) increased from 57 to 93%. The lattice constants a0, and bond length \(d_{Ga^{3+}-Fe^{2+}[Ni^{2+}]}\) on A-site and B-site decreased linearly with increasing Ni concentration. From the temperature dependence of susceptibility χ in zero-field-cooled and field-cooled magnetization under 400 Oe, with increasing Ni concentration, the sample showed a decrease in the freezing temperature Tf. Mossbauer spectra of all samples at room temperature showed 2-sets (A-site, and B-site) with large electric quadrupole splitting. The Mossbauer absorption area ratio of A-site decreased, while that of B-site increased with increasing Ni concentration, which is accord with the Rietveld refinement analysis of the XRD results.

Synchrotron radiation based Mössbauer absorption spectroscopy of various nuclides

Synchrotron-radiation (SR) based Mossbauer absorption spectroscopy of various nuclides is reviewed. The details of the measuring system and analysis method are described. Especially, the following two advantages of the current system are described: the detection of internal conversion electrons and the close distance between the energy standard scatterer and the detector. Both of these advantages yield the enhancement of the counting rate and reduction of the measuring time. Furthermore, SR-based Mossbauer absorption spectroscopy of 40K, 151Eu, and 174Yb is introduced to show the wide applicability of this method. In addition to these three nuclides, SR-based Mossbauer absorption spectroscopy of 61Ni, 73Ge, 119Sn, 125Te, 127I, 149Sm, and 189Os has been performed. We continue to develop the method to increase available nuclides and to increase its ease of use. The complementary relation between the time-domain method using SR, such as nuclear forward scattering and the energy-domain methods such as SR-based Mossbauer absorption spectroscopy is also noted.

Nutations of magnetizations of sublattices and their role in the formation of Mössbauer spectra of antiferromagnetic nanoparticles

The continuum model of the magnetic dynamics of an ensemble of antiferromagnetic nanoparticles in the two-sublattice approximation has been generalized to the case of the exact solution of the equations of motion for magnetizations of sublattices. The nontrivial excitation spectrum of such particles in the form of four excitation branches corresponding to the normal modes of self-consistent precession of magnetizations of sublattices, as well as the continuous spectrum of nutations of magnetizations accompanying these modes, corresponds completely to quantum-mechanical calculations and makes it possible to give a phenomenological interpretation of macroscopic quantum effects earlier observed in many experimental Mossbauer absorption spectra.

Mössbauer studies of the N50 permanent magnet

The crystal and the magnetic properties of the N50 permanent magnet, which is widely used in industrial applications, have been studied by using x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mossbauer spectrometer. The crystal structure was determined to be tetragonal with a Nd-Fe-B structure. Based on the M-T curves, the values of spin reorientation temperature (T SR ) and Curie temperature (T C ) were found to be 130 and 600 K, respectively. The Mossbauer spectra of N50 showed abrupt changes in the magnetic hyperfine field (H hf ) and the electric quadrupole shift (E Q ) at temperatures around 130 K, indicating a spin reorientation (T SR ). From the Mossbauer absorption area as a function of the square of the temperature for the N50 permanent magnet, the Debye temperature (Θ D ) was found to be Θ D = 414.7 K.

Interrelation of the Phase Composition and Durability of More than 800 Year Old Brick for the Example of the Kazan Kremlin

Research has shown that mullite in brick from the Kazan kremlin crystallizes in the form of primary (‘flaky’) mullite, pseudomorphs of glass with needle-shaped mullite in terms of feldspar, and pseudomorphs of glass with short-prismatic mullite. Mossbauer absorption spectra showed that in the brick studied mainly hematite was found on the surface and magnetite in the interior volume.

Equation of state and structural phase transitions in iron-based Ba3TaFe3Si2O14 langasite at high hydrostatic pressures

Synchrotron X-ray diffraction studies of the structural characteristics of Ba3TaFe3Si2O14 langasite are performed at high hydrostatic pressures (up to 60 GPa) created in a diamond anvil cell. At pressures up to 20 GPa, the Mossbauer absorption spectra for 57Fe nuclei and the Raman spectra are recorded. Two structural phase transitions at P ≈ 5.5 and 20 GPa are observed. The first transition corresponds to the displacements of light oxygen atoms and to an increase in the local symmetry of 3f oxygen tetrahedra surrounding iron ions. The second one is accompanied by a pronounced change in the lattice parameter c, and the unit cell volume undergoes a stepwise drop as large as 8.6%. An appreciable decrease in the parameter c at the structural transition should result in a significant increase in the exchange coupling constants between iron ions in neighboring ab planes underlying the giant increase in the Neel temperature in this crystal at pressures exceeding 20 GPa.

Low-Temperature Molecular Motions in Phospholipid Bilayers in Presence of Glycerol as Studied by Spin-Echo EPR of Spin Labels

Glycerol is used as a cryoprotective agent to protect biological systems under freezing conditions. Electron spin echo (ESE) spectroscopy, a pulsed version of EPR, is capable of studying low-temperature molecular motions of nitroxide spin labels. ESE technique was applied to study molecular motions in phospholipid bilayers prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) with added spin-labeled lipids 1-palmitoyl-2-stearoyl-(n-DOXYL)-sn-glycero-3-phosphocholine (n-PCSL, n was optionally 5 or 16). Bilayers were hydrated (solvated) either in pure water or in a 1:1 v/v water–glycerol mixture. In the used ESE approach, there were studied stochastic (or diffusive) orientational vibrations of the molecule as a whole (i.e., stochastic molecular librations). The anisotropic contribution to the echo decay rate, W anis, was measured, which is proportional, according to theory, to the product of the mean-squared angular amplitude \(\langle \alpha^{ 2} \rangle\) and the correlation time τ c. W anis was found to be small below and to sharply increase above 200 K, for the both types of solvents and the both label positions. As compared with hydration by pure water, in presence of glycerol W anis was larger for the 5th label position while for the 16th one it did not change. Also, for the 5th label position W anis values were found to be nearly the same as those for a polar spin probe 3,4-dicarboxy-PROXYL which was separately added to the bilayer as a reference and which is assumed to be partitioned only into the solvating shell. These results indicate that motions at the surface of bilayer are governed by the motion of solvating shell while motions in the bilayer interior occur independently. The relation of the obtained data with the dynamical transition phenomenon that is known for biological substances near 200 K from neutron scattering and Mossbauer absorption is discussed.

Coexistence of long range magnetic order and intervalent state of Eu in EuCu2(Si x Ge1 − x )2: Evidence from neutron diffraction and spectroscopic studies

Experimental results of the Xray absorption spectr oscopy, Mossbauer spectroscopy (isomer shift) and neu� tron diffraction are presented for the series of EuCu2(SixGe 1- x)2 polycrystalline samples (0 < x < 0.75). Homogeneous intermediate valence state is established for Eu ions as well as long range magnetically ordered state at the temperatures below 10-15 K. Observation of the ordered magnetic moments at Eu site gives rise to the experimental statement for the coexistence of valence fluctuations and long range magnetic order takes place in the wide range of Ge concentrations for this substance.

Observation of the double optical-gamma resonance in Mössbauer spectra of 151 Eu in EuP 5 O 14 single crystal

A theoretical analysis has been made and calculation procedures have been developed for describing the hyperfine structure of 151Eu Mossbauer spectra and the effect of double optical-gamma resonance (DOGR) in the presence of hyperfine quadrupole interaction with an arbitrary symmetry of the electric field gradient tensor. An experimental setup was designed for DOGR-effect observation, incorporating the pumping argon laser and the tunable dye laser combined with the Mossbauer spectrometer on a common platform. The Mossbauer absorption spectra of 151Eu3 + nuclei in single crystals of europium pentaphosphate, EuP5O14, have been measured at T = 5 K and 80 K under the absence and presence of optical pumping tuned to the 7F\(_{0}-^{5}\)D0 electronic transition at the 578 nm wavelength. A simultaneous analysis of these spectra in terms of the spin Hamiltonian of hyperfine quadrupole interaction has allowed us to evaluate the DOGR-effect magnitude with the population of the excited (5D0) electronic state under optical pumping of about 10 %.

Cation ordering in Sr(Fe1 − x Co x )0.9Ga0.1O2.5 with brownmillerite structure

Samples of solid solutions of the series Sr(Fe1 − x Co x )0.9Ga0.1O2.5 with brownmillerite structure are produced from appropriate amounts of oxides Fe, Co, Ga, and SrCO3 in different gaseous media and temperature conditions using solid-phase synthesis. Features of the distribution of cations over nonequivalent positions of the crystalline structure of the obtained samples are studied using the 57Fe Mossbauer absorption and emission spectroscopy.

Enhancing vibration measurements by Mössbauer effect

The measurement of the Mossbauer effect in a system excited with a periodic perturbation can provide information about it. For that purpose, the Mossbauer absorption of a source-absorber set which hyperfine parameters are well known, is measured at a constant relative velocity (i.e. at a defined spectral energy). The resulting Mossbauer absorption periodic signal provides information of the sample ac perturbation response. This approach has been used time ago to measure small tympanic vibrations (mechanical perturbations). In this work we present an extension of the vibration experiments, by measuring them at various absorber-source relative velocities within a constant-velocity strategy. As a demonstration test, the frequency response of a piezoelectric diaphragm in the 100 Hz–5 kHz range is obtained with a custom electronic counter. The experiments are performed using a 57Co(Rh) source and a 25-μm-thick stainless-steel absorber fixed to a piezoelectric diaphragm. Phase shifts and amplitude vibrations with velocities in the range from 1.5 μm/s to 20 mm/s are well characterized, extending the linearity limit well beyond the earlier suggested one of 1 mm/s.

Formation of magnetic nanoparticles studied during the initial synthesis stage

The formation of iron oxide nanoparticles in course of a sol-gel preparation process was traced by UV/Vis and 57Fe Mossbauer absorption spectroscopy. Samples were extracted at different stages of the reaction. While spectra measured on samples extracted at low reactor temperatures showed the starting materials Fe(acac)3 diluted in benzyl alcohol undergoing slow paramagnetic relaxation, a sample extracted at a reactor temperature of 180 °C gave clear evidence for emerging iron oxide nanoparticles. A prolonged stay at 200 °C results in a complete transformation from Fe(acac)3 to maghemite nanoparticles.

Structural features of green cobalt(III) hydroxide

Emission Mossbauer and X-ray absorption XANES/EXAFS spectroscopic techniques are applied to elucidate the structural features of green cobalt(III) hydroxide. A comparative analysis of structurally characterized cobalt(II) and cobalt(III) oxo-compounds shows that the parameters of the local environment of cobalt atoms in green cobalt(III) hydroxide differ substantially from those of its analogues.

On the thermodynamics of antiferromagnetic nanoparticles by example of Mössbauer spectroscopy

A quantum-mechanical model has been developed for describing the thermodynamics of an ensemble of ideal antiferromagnetic nanoparticles in the approximation of slowly relaxing macrospins of magnetic sublattices. This model is the foundation for the further development of the general theory for the magnetic dynamics of antiferromagnetic and ferrimagnetic nanoparticles. Moreover, it already allows a qualitative description of the difference between the thermodynamic properties of nanoparticles of different magnetic natures, including quantum effects, which have been observed for almost fifty years in many experimental Mossbauer absorption spectra of 57Fe nuclei in antiferromagnetic nanoparticles.

Multilevel relaxation model for describing the Mössbauer spectra of nanoparticles in a magnetic field

A theory is developed for the Mossbauer absorption spectra of an ensemble of single-domain particles in a magnetic field. This theory is based on the generalization of a relaxation model with a quantummechanical description of the stationary states of a particle and on the formalism of Liouville operators for describing the hyperfine interaction for a hyperfine field changing in both the magnitude and direction for various stationary states. The general scheme of calculating relaxation Mossbauer spectra in terms of a standard stochastic approach is substantially optimized using operations with block matrices and a unique tridiagonalization of high-rank non-Hermitian matrices with a simple nonorthogonal transformation in the calculation procedure. The resulting model can easily be implemented on a personal computer. It considers the physical mechanisms of formation of a hyperfine structure in a spectrum of nanoparticles in a real situation and self-consistently describes the qualitative features of the nontrivial evolution of spectra with the temperature and the magnetic-field direction and strength, which has been detected in 57Fe nucleus experiments performed on magnetic nanoparticles for half a century.