Mossbauer Effect Research Articles

Stochastic hyperfine interactions modeling library

The stochastic hyperfine interactions modeling library (SHIML) provides a set of routines to assist in the development and application of stochastic models of hyperfine interactions. The library provides routines written in the C programming language that (1) read a text description of a model for fluctuating hyperfine fields, (2) set up the Blume matrix, upon which the evolution operator of the system depends, and (3) find the eigenvalues and eigenvectors of the Blume matrix so that theoretical spectra of experimental techniques that measure hyperfine interactions can be calculated. The optimized vector and matrix operations of the BLAS and LAPACK libraries are utilized; however, there was a need to develop supplementary code to find an orthonormal set of (left and right) eigenvectors of complex, non-Hermitian matrices. In addition, example code is provided to illustrate the use of SHIML to generate perturbed angular correlation spectra for the special case of polycrystalline samples when anisotropy terms of higher order than A 22 can be neglected. Program summary Program title: SHIML Catalogue identifier: AEIF_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEIF_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU GPL 3 No. of lines in distributed program, including test data, etc.: 8224 No. of bytes in distributed program, including test data, etc.: 312 348 Distribution format: tar.gz Programming language: C Computer: Any Operating system: LINUX, OS X RAM: Varies Classification: 7.4 External routines: TAPP [1], BLAS [2], a C-interface to BLAS [3], and LAPACK [4] Nature of problem: In condensed matter systems, hyperfine methods such as nuclear magnetic resonance (NMR), Mössbauer effect (ME), muon spin rotation (μSR), and perturbed angular correlation spectroscopy (PAC) measure electronic and magnetic structure within Angstroms of nuclear probes through the hyperfine interaction. When interactions fluctuate at rates comparable to the time scale of a hyperfine method, there is a loss in signal coherence, and spectra are damped. The degree of damping can be used to determine fluctuation rates, provided that theoretical expressions for spectra can be derived for relevant physical models of the fluctuations. SHIML provides routines to help researchers quickly develop code to incorporate stochastic models of fluctuating hyperfine interactions in calculations of hyperfine spectra. Solution method: Calculations are based on the method for modeling stochastic hyperfine interactions for PAC by Winkler and Gerdau [5]. The method is extended to include other hyperfine methods following the work of Dattagupta [6]. The code provides routines for reading model information from text files, allowing researchers to develop new models quickly without the need to modify computer code for each new model to be considered. Restrictions: In the present version of the code, only methods that measure the hyperfine interaction on one probe spin state, such as PAC, μSR, and NMR, are supported. Running time: Varies

Charge transfer in FeOCl intercalation compounds and its pressure dependence: An x-ray spectroscopic study

We present a study of charge transfer in Na-intercalated FeOCl and polyaniline-intercalated FeOCl using high-resolution x-ray absorption spectroscopy and resonant x-ray emission spectroscopy at the Fe-K edge. By comparing the experimental data with ab-initio simulations, we are able to unambiguously distinguish the spectral changes which appear due to intercalation into those of electronic origin and those of structural origin. For both systems, we find that about 25% of the Fe sites are reduced to Fe2+ via charge transfer between FeOCl and the intercalate. This is about twice as large as the Fe2+ fraction reported in studies using Mossbauer spectroscopy. This discrepancy is ascribed to the fact that the charge transfer occurs on the same time scale as the Mossbauer effect itself. Our result suggests that every intercalated atom or molecule is involved in the charge-transfer process, thus making this process a prerequisite for intercalation. The Fe2+ fraction is found to increase with pressure for polyaniline-FeOCl, hinting at an enhancement of the conductivity in the FeOCl intercalation compounds under pressure.

The superexchange interactions in mixed Co–Fe ludwigite

The crystal structure, cation distribution and exchange interactions in the Co 2.25Fe 0.75O 2BO 3 ludwigite have been explored through X-ray diffraction, electrical resistivity, ac-susceptibility and Mossbauer effect measurements. The crystal data have shown that iron atoms occupy the most symmetric crystallographic sites Fe4 and Fe2. The complex magnetic behavior with two magnetic transitions near 70 and 115 K at low temperatures was found. The Mossbauer data have displayed the trivalent iron states only. The values of superexchange energies have been estimated for Co 3O 2BO 3 and Co 2.25Fe 0.75O 2BO 3 yielding a significant role of frustrations in the ludwigite magnetic system. Variable range Mott hopping conductivity law was proved to be valid in the wide temperature region, pointing out a localized character of charge carriers rather than collective.

Mössbauer effect studies of Tb0.27Dy0.73(Fe1−x Co x )2 intermetallics at 295 K

The synthesis of materials and the studies of crystal structure and 57Fe Mossbauer effect were performed for Tb0.27Dy0.73(Fe1−xCox)2 intermetallics. Terfenol-D (Tb0.27Dy0.73Fe2) is the starting compound of this Fe/Co-substituted series. X-ray measurements showed evidence of a pure cubic Laves phase C15, MgCu2-type, and unit cell parameters were determined across the series. A Co substitution introduced local area, at sub-nanoscale, with random Fe/Co neighbourhoods of the 57Fe atoms.

Magnetic and Mössbauer Studies of Ba(Fe1−x Ni x )2As2 Single Crystals

Magnetization and 57Fe Mossbauer effect spectroscopy (MS) studies of Ba(Fe1−xNix)2As2 single crystals (x=0 to 0.054) at temperatures (5 K to 300 K) have been performed. Magnetic measurements show that for BaFe2As2 the magnetic moment decreases below TN=136 K. TN is suppressed monotonically by Ni doping. On the other hand, for higher x values the magnetic moment increases below TN. Unexpectedly for x=0.024 (TN=67 K), the virgin zero-field-cooled (ZFC) curve is higher than that of field-cooled (FC) one below 48 K. The magnetic MS spectra of this sample are composed of a superposition of two subspectra, corresponding to commensurate and incommensurate field distributions. The average magnetic hyperfine field Heff decreases with T and becomes zero at 80 K. For higher x values, the samples become superconducting at TC=15.5 and 19 K for x=0.046 and 0.054, respectively. For both samples below TC, the FC curves are positive (the paramagnetic Meissner effect) up to applied field of H∼15 Oe and the susceptibility is inversely proportional to H. The MS spectra below and above TC are almost identical, indicating that the MS parameters are not sensitive enough to detect the superconducting state. The peculiar phenomena observed are attributed to disorder induced by the presence of Ni atoms in the Fe sublattice.

ChemInform Abstract: The Local Magnetic States in Spin-Ordered Amorphous and Crystalline Alloys

The review of experimental investigations of local magnetic states is given for three types of spin ordered materials: the cubic Laves phases with C15 structure, multicomponent heterophase alloys of Nd-R-Fe-M-B type and Heusler alloys. To obtain information on local magnetic states several kinds of experimental techniques were used: measurements of nuclear specific heat at T<1K. Mossbauer effect, nuclear spin-echo. The obtained results are treated in terms of several theoretical models and some essential parameters of itinerant and localized electron spectra are estimated and discussed.

ChemInform Abstract: Magnetic Properties of Tm2Fe17Nx Studied by Means of the 169Tm and 57Fe Moessbauer Effect.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Fe-Mo Catalysts with High Resistance to Carbon Deposition During Fischer–Tropsch Synthesis

Effects of Mo addition on the Fischer–Tropsch synthesis (FTS) performance of precipitated Fe and FeCu catalysts were tested at 280 °C, 1.5 MPa, H2/CO = 2.0, 2,000 h−1. Reaction results in fixed-bed reactor indicate that Mo addition stabilizes the selectivity to higher molecular-weight hydrocarbons of Fe and FeCu catalysts. Carbonaceous species over the spent catalysts were studied by Mossbauer effect spectroscopy (MES) and temperature-programmed hydrogenation (TPH). It is found that Mo addition inhibits the carbon deposition on iron catalysts surface during the FTS reaction and thus probably protects the active sites for producing heavy hydrocarbons. Mo addition inhibits the carbon deposition on iron catalysts surface during the Fischer–Tropsch synthesis and thus protects the sites for production of heavy hydrocarbons and stabilizes the selectivity to higher molecular-weight hydrocarbons (C5 +).

Dielectric, magnetoelectric, structure, and dissipative properties and the Mössbauer effect in PbFe1/2Nb1/2O3 ceramics in wide frequency and temperature ranges

High-quality fine-grained ceramic samples of classical multiferroics PbFe1/2Nb1/2O3 (PFN) were synthesized. Their dielectric, magnetoelectric, and magnetic characteristics, including the Mossbauer effect, were measured over wide ranges of temperatures (10–1000 K) and field frequencies (from 25 Hz to 1 MHz). The temperature dependence of the dielectric loss exhibits a maximum between 150 and 170 K, likely due to magnetic ordering. The dependence of ɛ on the magnetic field displays an anomalous increase near the Curie temperature (370 K) that rises to 40% upon heating.

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

Abstract New germanosilicate glasses giving the crystallization of yttrium iron garnet Y 3 Fe 5 O 12 (YIG) and Bi-doped YIG, 23Na 2 O– x Bi 2 O 3 –(12− x )Y 2 O 3 –25Fe 2 O 3 –20SiO 2 –20GeO 2 (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mossbauer effect measurements that iron ions in the glasses are present mainly as Fe 3+ . It is suggested from the X-ray diffraction analyses and magnetization measurements that Si 4+ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32–60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO 4 fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe 3+ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.

NMR and Mössbauer study of multiferroic BiFeO3

Pulse nuclear magnetic resonance (NMR) was applied in studying the effect of 57Fe isotope content in multiferroic BiFeO3 on the shape of NMR spectra at 4.2 K. Strong dependences of the NMR line shape on the isotope content and transverse relaxation time were found. Consideration of these effects on NMR line shape shows that there is an undisturbed (with no anharmonicity effect) space spin-modulated structure of the cycloid type in BiFeO3. The Mossbauer effect was also used to investigate the perovskite BiFeO3 at 650, 295, and 87 K. Experimental spectra allowed us to obtain the distribution of hyperfine fields, which was found to be consistent with studies of the NMR line shape. The local electronic and magnetic states of the iron ion were measured.

Will the iron age of superconductivity become the Mössbauer age?

The discovery of new iron-containing high-temperature superconductors is considered in relation to their studies by means of the Mossbauer effect. The importance of the relevant results for the problem of the coexistence of magnetism and superconductivity and the stability of superconductivity against to disorder is shown by analyzing the available literature data.

Aftereffects of “Magnetic impact” in Nd2Fe14B

The phenomenon of cyclic local magnetostriction was observed in Nd2Fe14B metallic crystal, activated by a magnetic field pulse, by means of the Mossbauer effect. Fluctuations in hyperfine fields, isomeric displacements, and the occupancy of certain positions of Fe atoms in the structure occurred with a periodicity of ∼12–13 days. After ∼190 days, the fluctuations ceased and there was an inversion in the occupancy of structurally nonequivalent Fe positions.

Study of Electroslag Remelted and Nitrogen Containing High Speed Tool Steel M41

Mossbauer Effect (ME) spectra, microstructure and hardness of some alloyed and conventional AISI M41 high speed tool steel samples produced by induction furnace as well as after doing electro-slag refining (ESR) process under different slag compositions have been investigated. The obtained ME spectra for all samples could be analyzed to a singlet and three sextets. The appeared singlet in the conventional steel and that alloyed with nitrogen as well as two refined samples using electro-slag remelting 1 and 2 (ESR1, M41N and ESR2, M41N) can be attributed to γ–austenite phase, while the singlet that appeared in the refined sample 3 (ESR3, M41N) can be attributed to some iron nitride of the form ( e-Fe2N). In the refined sample, which does not contain nitrogen, γ–austenite phase cannot be found and some α-Fe2O3 was detected. The observed three sextets were attributed to three different magnetic martensite phases. It appeared also that some transformations in between the three martensite phases and between martensite and austenite take place, and all these changes were thoroughly discussed. It is interesting to state that the obtained ME results are in agreement with those obtained from optical microscopy and micro-hardness measurements.

Advanced Moessbauer Spectroscopy by Using Nuclear Resonant Scattering of Synchrotron Radiation

Mossbauer spectroscopy is a powerful and well established method for wide variety areas of researches, such as physical-, chemical-, biological-, and earth-sciences. One of the most outstanding features of this method is that element specific measurement is possible. Particularly, by using synchrotron radiation, we can measure Mossbauer effect without preparing radioactive Mossbauer sources and, therefore, element specific measurement is attained. Moreover, the use of synchrotron radiation allows us to measure element- and site-specific phonon density of states. In this article, the concept of the Mossbauer spectroscopy using synchrotron radiation and nuclear resonant inelastic scattering spectroscopy is reviewed. In particular, a new method that gives absorption Mossbauer spectra using synchrotron radiation and is applicable for almost all the Mossbauer nuclides is introduced. The features of these methods for the study of condensed matter science including surface science are discussed.

Microwave Spectroscopy of Condensed Helium at the Roton Frequency

A spectral absorption line of electromagnetic radiation in the frequency range 40–200 GHz and at temperatures 1.4–2.75 K is measured in liquid helium. It is found that the narrow line of resonance absorption near the roton frequency does exist against a wide pedestal. The results obtained are compared with the data on the roton spectrum obtained in neutron scattering experiments. The possible reason for narrow absorption peak appearance is analyzed and the analogy between the observed phenomenon and Mossbauer effect is considered.

Coherent and incoherent metamaterials and order-disorder transitions

We demonstrate a new class of "coherent" metamaterials, where a regular ensemble of meta-molecules shows a collective, i.e. coherent, narrow band resonant response, while disordering the ensemble leads to broadening and eventually disappearance of the resonance. We draw parallels between the observed collective behavior of meta-molecules and the Mossbauer effect and notice certain remarkable similarities with the phase transitions of ferromagnetic systems.

Space-time analysis of the Mössbauer radiation scattering

Microscopic theory of the Mossbauer effect is formulated. Nuclei interactions with local magnetic fields and lattice vibrations are taken into account. The analysis is based on the precisely solvable quantum mechanical model of Mossbauer scattering. The process of Mossbauer photon emission and its subsequent scattering on one and two nuclei are analyzed in detail. It is shown that some phenomenological concepts proposed for explanation of fine experiments with 109 Ag nuclei do not obtain microscopic justification.

Coupling Of Solvent And Protein Dynamics: Mossbauer And Incoherent Neutron Scattering From Dielectric Relaxation Data

A wide variety of protein dynamics are accounted for by two classes of solvent processes: the bulk-solvent viscosity and hydration-shell dynamics. In glass-forming solvents the bulk viscosity arises from the well-characterized microscopic alpha relaxation; in liquid solvents that freeze the alpha process is essentially molecular reorientation. In past work we showed that the solvent alpha relaxation determines the activation enthalpy of alpha-slaved protein motions.We have now measured the dielectric spectrum of the hydration-shell dynamics in myoglobin solutions as a function of hydration, temperature and frequency. These hydration-shell data and a minimal model of protein-solvent coupling predict the temperature- and hydration-dependence of the Mossbauer effect. Furthermore, we show agreement between incoherent neutron scattering data and our measurements of hydration dynamics.These improvements in understanding protein-solvent dynamical coupling will be discussed in terms of earlier work describing the slaving of many protein functional motions to the solvent alpha-process and the slaving of protein folding. We demonstrate that many enthalpy barriers to protein motion arise almost entirely from solvent dynamical processes.

Ion bombardment of Fe-based amorphous metallic alloys

Fe74Cu1Nb3Si16B6 amorphous metallic alloy is investigated after ion irradiation by 110 keV N + and 593 MeV Au ions. The depth-profiles of the radiation damage were calculated by the SRIM2008 code. Applicability of transmission and conversion electron Mossbauer effect measurements to distinguish between the bulk and surface radiation damage is demonstrated by using different irradiation conditions. The investigated alloy is characterized by ferromagnetic interactions. The implantation does not depict appreciable changes of the samples’ surfaces. Changes in chemical short-range order (SRO) are revealed in N + irradiated alloys. Heavy Au ions caused pronounced effects in the position of the net magnetization though no impact on SRO was observed. After annealing, structural relaxation and annealing-out of the irradiation-induced stresses caused the rotation of the net magnetization back to its original position.