Mossbauer Effect Spectra Research Articles

Experimental and theoretical investigation of the effect of milling time on the magnetic properties of mechanically alloyed FeAlNi (wt%) powders

Powders of Fe50Al30Ni20 (wt%) are being milled in a P7 high-energy planetary ball mill to determine the effect of milling time on magnetic properties. In order to track changes in morphology and magnetic properties, SEM, magnetic measurements, and Mossbauer spectroscopy were employed during milling. Multiple phases are present; B2-(Fe, Ni)Al dominates, and Fe(Ni, Al) is second in strength. This indicates that they are paramagnetic at room temperature based on the Mossbauer effect spectra after 8 h of milling. The coercivity Hc and saturation magnetization, on the other hand, remains finite values in magnetic measurements. The CASTEP (Cambridge Serial Total Energy Package) code was used to investigate magnetic behavior further.

Investigations on microstructure, electrical and magnetic properties of Ni–Zn–Ga spinel ferrites

Two spinel ferrite samples Ni0.7Zn0.3GayFe2–yO4 (y = 0.5, 1.0) were prepared by both ceramic and citrate methods. X-ray diffraction patterns indicated a single phase of cubic structure for all the samples that have a space group Fd-3m. Rietveld analysis using MAUD software for all samples showed that the lattice parameter (a) decreases, while oxygen parameter (U) and strain (ɛ) increase by increasing the amount of Ga. A marked increase in the frequency bands in both the tetrahedral and octahedral sites was observed in the vibrational frequency bands of Fourier transform infrared spectra. Mossbauer effect (ME) spectra recorded at room temperature for the bulk sample (prepared by ceramic method) with lower concentrations of Ga3+ (y = 0.5) consist of two Zeeman sextets. ME spectra for the other bulk sample (y = 1.0) and the two samples in nanoscale (prepared by citrate method) can be fitted by one and two doublets due to the paramagnetic and superparamagnetic behaviour, respectively. Vibrating sample magnetometer measurements showed that the saturation magnetization (Ms) obtained from the hysteresis loop is decreased by increasing Ga3+ concentration for all the samples. The coercivity (Hc) is inversely proportional to the particle size (D) for bulk samples. Nevertheless, Hc of the nanoscale samples enhanced by increasing the particle size. The size dependence of Hc is an indication of the superparamagnetic characteristics supported by ME. The ac electrical conductivity (ln $$ \sigma $$ ), dielectric constant (e′) and dielectric loss tangent (tan δ) were studied at different frequencies and temperatures for the investigated samples. The obtained results showed that the conductivity for all samples increases with increasing temperature in a behaviour similar to that of the most semi-conductor materials.

Influence of Bi2O3 on the physical and electrical properties of some Boro-Iron glasses

The rapid quenching method was used to prepare some of Bismuth Boro-Iron glasses doped with a constant amount of iron ions. The melting temperature adjusted to be about 1000±50°C. The obtained glasses were characterized by X-ray diffraction (XRD), FTIR and Mossbauer Effect (ME) spectra. Both of XRD and ME showed that all samples of x<15 had formed pure glass phases, while the sample of x=15 exhibited crystalline phase embedded in an amorphous structure. DC activation energy was observed to increase as Bi content increase. Cole-Cole parameters referred to a distribution of the relaxation time. The refractive index as the Bi ion was increased.

Structural Study of Glass and Glass Ceramics Prepared with Egyptian Basalt

Egyptian basalt rock was used to prepare some glasses with different additives of Na2O by the melt quenching method. The prepared glasses were characterized applying FTIR, XRD and Mossbauer Effect (ME) spectroscopy. XRD indicated that all the samples showed a homogeneous glassy phase except the sample containing 35 mol % of Na2O which showed a very small crystalline phase of less than 5 %. FTIR measurements indicated the presence of various structural units including SiO4, FeO4 and AlO4. ME hyperfine parameters indicated the presence of both Fe2+and Fe3+in the low Na2O content glasses (the first three samples), while the iron in the high Na2O content glasses (the last three samples) showed only the Fe3+ state. All the glass samples were heated at 900°C for 6 h, of which XRD analysis showed different crystallites of nanometer size. ME spectra of the heat-treated (HT) samples indicated the presence of magnesium ferrites as confirmed by XRD study.

Preparation and Characterization of Zinc-Containing Nickel Gallate Ferrite

Polycrystalline Ni1−xZnxFeGaO4 samples containing different amounts of zinc (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by solid-state reaction. Study of the crystal structure by x-ray diffraction (XRD) revealed peaks typical of a single-phase polycrystalline face-centered cubic structure (FCC). Elemental composition was determined by x-ray fluorescence (XRF) analysis. Fourier-transform infrared (FTIR) spectra contained two absorption bands related to the tetrahedral A and octahedral B sites of the spinel ferrite. Magnetization loops obtained by vibrating sample magnetometry (VSM) indicated that the saturation magnetization, Ms, decreased gradually with increasing in Zn content (x), and that coercivity Hc was related to the microstructure of the Zn-doped samples. Mossbauer effect (ME) spectra of the samples were broad and magnetically split for x = 0.0 and 0.1 and quadruple doublets for the other Zn2+ concentrations. The dielectric constant (e′) and dielectric loss tangent (tan δ) were also measured over wide ranges of frequency and temperature by use of the two probe method. The results were explained on the basis of cation–anion–cation and cation–cation interactions through the metal sites in the Ni–Zn–Ga ferrites.

Structural and Magnetic Study of Zn-Substituted NiGa y Fe 2−y O 4 Ferrite

Single-phase spinel ferrite Ni 1−x Zn x Ga y Fe 2−y O 4 with (0.0≤x≤0.5) and y=0.5 samples were synthesized using solid-state reaction technique. These ferrites were investigated using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mossbauer effect (ME) spectroscopy. XRD patterns confirmed the formation of single-phase cubic spinel ferrites for all samples. Lattice parameter was found to decrease with the introduction of Ga 3+ in NiFe 2 O 4, and then to increase with the increasing of Zn 2+ content x. ME measurements illustrated a strong dependence on the zinc concentration. The cation distribution calculated from the ME spectra at room temperature indicated that the Ga 3+ ion substituted iron in both octahedral B and tetrahedral A- sites. Zn 2+ ions firstly introduced in A- site, and for higher x, they distribute in both B- and A- sites. VSM measurements indicated that the change in the value of saturation magnetization can be explained using the cation distribution obtained from ME measurements. The coercivity values can be interpreted on the basis of magneto-crystalline anisotropy.

Grain size effects on the magnetic properties of ZnxMn1−xFe2O4 nanoferrites

Abstract Single phase nanoferrites bearing the chemical formula ZnxMn1−xFe2O4 (0≤x≤1.0) have been produced under low reaction temperature of 200 °C. The compounds were characterized by X-ray diffraction, Mossbauer and SQUID measurements. The particle size varies between 5 nm and 14 nm. The particle size dependence of the magnetic properties is investigated. Our results indicate spin-glass behavior at temperatures between 100 K and 200 K. The variation of Zn concentration has also significant effects on the structural and magnetic properties. The complex variation of lattice parameter with x is explained on the basis of redistribution of Zn atoms in both tetrahedral (A) and octahedral (B) sites. The 57Fe Mossbauer effect spectra show paramagnetic spin state in all the compounds.

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.

In Situ Surface-Enhanced Raman Scattering Studies of the Nitrosyl Adduct of Hemin Adsorbed on Roughened Silver Surfaces in Aqueous Electrolytes

Modifications in the electrochemical and spectral properties of hemin (Hm) adsorbed on roughened Ag electrodes in an aqueous electrolyte (phosphate buffer, pH 3) induced by brief exposure to mildly acidic solutions containing NO have been examined by in situ surface-enhanced Raman scattering (SERS) using Q band excitation (λexc = 532 nm). Two lines of evidence support the formation of the adsorbed nitrosyl adduct of Hm (NO−Hm) under the conditions employed for these experiments: the complete disappearance of the characteristic voltammetric redox peaks of Hm centered at ca. −0.25 V versus SCE, and a significant drop in the intensity, I, of the ring-based ν30 mode at 1165 cm-1 in the in situ SERS spectrum compared to that of adsorbed Hm under the same conditions. Such a decrease in the intensity of the I(ν30) mode was also found in the solution phase Raman spectrum of Hm in THF and DMF upon NO exposure. Notably absent from the SERS spectrum were features attributable to vibrational modes due to NO and Fe−NO, which are clearly discernible for NO iron macrocyclic adducts in solution phase using Soret band excitation (λexc = 413 and 406 nm). Scanning to sufficiently negative potentials led to the reemergence of the Hm redox peaks and restored the I(ν30) mode in the SERS spectrum recorded at potentials that were positive enough for the reduced form of Hm to undergo full oxidation. These observations clearly indicate that, to the level of sensitivity of these measurements, the formation and subsequent reduction of the adduct can be effected without compromising the integrity of Hm. Careful inspection of the data showed that the SERS spectrum of the NO−Hm adduct resembles that of adsorbed (axially uncoordinated) Hm, rather than its reduced counterpart, measured under otherwise identical conditions, suggesting that the electronic environment within the ring in the NO−hemin adduct and the (NO-free) oxidized Hm are similar. This behavior is in agreement with information derived from Mossbauer effect spectra for NO−Fe macrocyclic adducts.

A Fitting Procedure for Magnetic Multiphase Materials Mössbauer Spectra

In this work a practical method of fitting complex multiphase Mossbauer effect spectra is proposed. The task is simplified imposing specific restrictions to the analysing functions, which are appropriate for cases where the component phases spectra do not change substantially during the process under study. The ME spectra can be analysed using the phases subspectra, by defining only a reduced number of parameters. The constraints are equivalent to assume a Doppler velocity transformation v′=(v−δm)Bm0/Bm+δm0 for each phase, where δm and Bm are fitting parameters containing information on the phase mean isomer shift and hyperfine field and δm0 and Bm0 their reference values. In this manner physically meaningful results are easy to obtain. The idea was applied to partially nitrogenated R2Fe17Nx (R= Sm and Y) and partially hydrogen-decomposed Nd–Fe–B materials.

Microstructure of supersaturated fcc Al-Fe alloys: A comparison of rapidly quenched and mechanically alloyed Al98Fe2

Alloys of the composition Al98Fe2 have been prepared by rapid quenching from the melt and mechanical alloying methods and have been studied by X‐ray diffraction techniques and room temperature 57Fe Mossbauer effect methods. Results may be summarized as follows: The rapidly quenched sample is a single phase supersaturated fcc Al–Fe alloy. Mossbauer effect spectra indicate the presence of a substantially greater degree of Fe clustering than is expected for a random distribution of atoms on the lattice sites. Mechanically alloyed samples have been studied as a function of milling time and show the initial formation of a supersaturated fcc phase with microstructural properties which are quite similar to those of the rapidly quenched sample. Further milling results in the reduction of the average grain size and the formation of an amorphous phase. Mossbauer studies and previously reported phase diagrams suggest that a substantial fraction of the Fe resides in this phase.

A Mössbauer effect study of the interstitial hydrides and nitride of Nd2Fe17

The Mossbauer effect spectra of Nd2Fe17H3, Nd2Fe17H5, and Nd2Fe17N3 have been measured at several temperatures between 85 and 295 K and fitted with a model which is similar to that used for the analysis of the Mossbauer effect spectra of Nd2Fe17 and Nd2Fe17N2.6. The weighted average isomer shift increases in going from Nd2Fe17 to its hydrides and nitride, an increase which results mainly from the lattice expansion. The changes in the individual isomer shifts upon hydrogenation may be understood in terms of the expansion of the Wigner-Seitz cell volume and the presence of hydrogen or nitrogen near neighbors at a specific site. The 295 K weighted average hyperfine field increases from 157 kOe in Nd2Fe17 to 243 kOe in Nd2Fe17H3, 280 kOe in Nd2Fe17H5, and 318 kOe in Nd2Fe17N3, a sequence determined by the Curie temperatures. In contrast, the weighted average hyperfine field at 85 K and the saturation magnetization at 5 K for Nd2Fe17H3 are lower than those of Nd2Fe17, presumably because of thec-axis lattice contraction which occurs upon hydrogenation of this compound. The main difference between the effect of hydrogenation and nitrogenation resides in the substantial increase observed for the 9d and 18h hyperfine fields upon nitrogenation.

Mössbauer studies of DNF and FMA in a smectic B liquid crystal

Abstract The FE-57 Mossbauer effect (ME) was used to study two solutions 0.4 wt% of ferrocenyl-4′-methoxyaniline (FMA) in the liquid crystalline material 4-n-butoxybenzylidene-4′-n-octylaniline (40.8) and 0.4 wt% of 1,1′-dinonanoyl-ferrocence in 40.8. The ME parameters were determined for the temperature range 40-300 K in the crystalline solid phase and 40–220 K in the cold smectic B phase of 40.8 for both samples. The ‘cold smectic B’ is defined as the smectic B glass and the supercooled smectic B phase. For T < 60 K the DNF-40.8 system exhibited a ME spectrum that was composed of two quadrupole split doublets. This four-line spectrum was observed for both the crystal phase and the smectic B glass phase of the DNF-40.8 system. The FMA-40.8 system exhibited a single quadrupole doublet. The In (recoil-free intensity f) versus T data exhibited linear Debye behaviour for the solid phase over the entire temperature range. The cold smectic In f versus T data also exhibited Debye behaviour for this system. The ...

A Mössbauer effect study of Y2Fe17 and Y2Fe17N2.6

The Mossbauer effect spectra of Y2Fe17 and Y2Fe17N2.6, obtained at 85 K, are analyzed with a model consistent with their crystallographic structures and band structure calculations of their magnetic moments. The increases in the individual site isomer shifts and hyperfine fields upon nitrogenation correlate well with the increases in both the individual Wigner-Seitz cell volumes and the magnetic moments. The spectral analysis, which requires ten sextets, indicates that the magnetization lies in a general direction in the hexagonal basal plane of these compounds.

Mossbauer effect study of the effect of gamma irradiation on the behaviour of iron in sodium silicate glasses

The effect of gamma irradiation on the behaviour of iron in a sodium silicate glass system [40 mol% SiO2, 60 mol% Na2O and 1–6 mol% Fe2O3] was investigated by Mossbauer effect (ME) and electron spin resonance (ESR) techniques. The changes in the quadrupole splitting (QS), line width of the ME spectra and the intensity of the g = 4.2 absorption line of the ESR spectra, showed that the distribution of the charges around the Fe nucleus became more symmetrical and less distorted than before irradiation. The change in the Fe-O interatomic distance due to gamma irradiation was determined using the overlap contribution to isomer shift (IS) for the Fe3+ ion in both tetrahedral and octahedral sites. The aging effect on the relaxation time of the electric field gradient (EFG) at the iron nucleus in irradiated glass showed that the relaxation time is increased and after certain period recombination of the defects occurred.

Compositional control of plane group symmetry in tourmalines: an experimental and computer simulated TEM, crystallographic image processing and Mossbauer spectroscopy study

Tourmalines with different compositions show different plane group symmetries in experimental high resolution transmission electron microscopy (HRTEM) when projected along the c-axis. Fe-poor elbaite shows p31m symmetry, while Fe-bearing elbaite shows p3m1 symmetry. Rubellite shows p6 symmetry, while Fe-Mg-Al-bearing tourmaline shows a «pseudo» p6 type of symmetry. Symmetries p3m1 and p6 are not compatible with the space group R3m assigned to tourmaline from X-ray structural determination studies. The perturbations of symmetry from p31m to p6 and «pseudo» p6 depend on the magnitude of the scattering amplitude of the atoms occupying the 3a and 9b sites. Furthermore, computer simulations of elbaite, schorl and dravite show different projected potentials for images down the c-axis. Regions with high mean concentration of light or heavy elements a few unit cells apart are common in Fe-poor elbaite. This results in a marked difference of the distribution contrast in the HRTEM image of elbaite. The Mossbauer effect (ME) spectra of tourmaline are different with different Mossbauer parameters, reflecting the difference in composition. Experimental HRTEM, computer simulation and ME indicate that composition controls symmetry, ME parameters and atomic coordinates in tourmaline, an observation not recorded in other minerals

Mössbauer effect studies of Hume-Rothery stabilization mechanisms in decagonal Al-Fe-Ni quasicrystals

Abstract Decagonal quasicrystals of the form Al75Fe25-xNix have been prepared by rapid solidification. These alloys were studied by X-ray diffraction and 57Fe Mossbauer effect methods. The Mossbauer effect spectra show nearly symmetric quadrupole-split doublets. The mean quadrupole splitting shows a monotonie inerease with inereasing Ni content. The mean isomer shift shows a maximum for the composition Al75Fe16Ni9. These Mossbauer effect parameter trends are described in terms of the Hume-Rothery stability criterion. The maximum in the isomer shift corresponds to a minimum in the 57Fes-electron density. This is related to the electron density, yielding a free-electron Fermi sphere with a diameter equal to that of the pseudo-Brillouin zone boundary as determined by X-ray diffraction studies.

Low temperature169Tm Mössbauer spectrum of the TmBa2Cu3O7−δ superconductor

A169Tm Mossbauer effect spectrum at 60 mK of the TmBa2Cu3O7−δ superconductor is a symmetric doublet characteristic of pure quadrupolar interaction. There is thus no evidence of Tm magnetic ordering in this material down to this temperature, in contrast to other rare-earth based “1-2-3” superconductors. The spectrum is fitted with crystal field parameters derived from those of the holmium-based superconductor, and values are found for shielding parameters.

A neutron diffraction and Mossbauer effect study of the (FeO2)n ferromagnetic sheets in antiferromagnetic alpha -Fe2(PO4)O

An unusual feature of the mixed-valance compounds alpha -Fe2(PO4)O is the presence of zig-zag chains of face-sharing octahedra running parallel to (010) and containing, alternately, Fe2+ and Fe3+ ions. These chains form sheets with the composition (FeO2)n and, because of the presence of face-sharing octahedra, have a very short Fe2+-Fe3+ distance of 2.92 AA. The magnetic properties of alpha -Fe2(PO4)O have been studied by powder neutron diffraction between 4.2 and 280 K and by the Mossbauer effect between 4.2 and 295 K. Below the Neel temperature of 218(3) K, the neutron diffraction data indicate a magnetostriction predominantly along the c-axis, magnetic moments at 4.2 K of 3.82 (4) mu B for Fe2+ and 4.26(5) mu B for Fe3+ oriented parallel to (010), and the presence of ferromagnetic sheets, containing the zig-zag chains, which are coupled into an overall antiferromagnetic structure. The net antiferromagnetic coupling is the result of a dominant 134 degrees Fe3+-0(1)-Fe3+ intersheet superexchange pathway. Ferromagnetic coupling dominates within the sheets and, as a result, the entire magnetic structure avoids any spin frustration. Above 220 K, the Mossbauer effects spectra are paramagnetic and show two quadrupole doublets with hyperfine parameters corresponding to the discrete Fe2+ and Fe3+ valence states. Below 220 K, the Mossbauer effect spectra show two magnetic components with hyperfine parameters characteristic of discrete Fe2+ and Fe3+ ions and in agreement with the corresponding paramagnetic values and the magnetic structure.

57Fe Mössbauer-effect studies of quadrupole splitting distributions in icosahedral Al-TM-Fe quasicrystals

Room temperature57Fe Mossbauer effect spectra of several Al-TM-Fe icosahedral quasicrystals are reported. Results of fits to discrete sites and to various distributions of quadrupole splittings are presented. Mean isomer shifts,\(\overline \delta \), and quadrupole splittings, Δ, are shown to be insensitive to the fitting procedure used. Trends in\(\overline \delta \) and\(\overline \Delta \) for the icosahedral phase may be indicative of a Hume-Rothery stabilization mechanism.