Mossbauer Spectroscopy Studies Research Articles

Development of a cell for in-situ/operando Mössbauer spectroscopy studies of Catalysts: Application to the characterization of iron nanoparticles used in Fischer-Tropsch reaction.

In this paper, we report the design of a stainless-steel cell with polyimide film windows for carrying out in situ Mossbauer spectroscopy studies with a horizontal x-ray beam. It allows recording spectra at pressures up to 0.2-0.3 MPa and temperatures up to 500 °C under a gas flow rate of up to 100 ml min-1. The catalyst is either directly deposited on the heating element or pressed into the form of a pellet for larger quantities. A wide range of heating or cooling rates can be used, and a very accurate sample temperature can be monitored for several days. An example of application to the study of a catalyst based on iron nanoparticles entrapped in silicalite-1 used for the Fischer-Tropsch reaction is presented to illustrate the use of the cell.

Specific Features of Grain Boundaries in Nickel Processed by High-Pressure Torsion

Publications on obtaining bulk nanostructured materials with special properties by various modes of severe plastic deformation, using nickel as an example, are briefly reviewed. Particular attention is paid to the state of grain boundaries, commonly referred to as nonequilibrium, or deformation-modified boundaries, revealed by electron microscopy, including scanning tunneling, Mossbauer spectroscopy, and diffusion studies. It is shown that contribution of specific state of grain boundaries to additional strengthening is often overestimated. In particular, in Ni processed by high pressure torsion, nonequilibrium grain boundaries are formed, which have increased energy and are ultrafast diffusion paths, but they contribute relatively little to the total strengthening.

Effect of La substitution on the structural and chemical properties of Barium hexaferrite via Mossbauer spectroscopy

M-type Barium hexaferrite is a famous hard magnetic material with a hexagonal crystal structure. La substituted Barium hexaferrite, Ba(1-x)La(x)Fe12O19, (where, x = 0.25 and 0.30) were synthesized using ball milling followed by sintering at 1300 °C for 5 hours. X-ray diffraction patterns reveal the formation of a single-phase magnetoplumbite structure of barium hexaferrite, which belongs to the P63/mmc space group. Mossbauer spectroscopic studies were carried out to study the magnetic phase, the effect of La doping on the valency of the Fe atom, and charge distribution in the prepared samples. Mossbauer spectra is fitted using 5 sextets, shows there is 5 sublattices present in the system. From the fitting of Mossbauer spectrum, it is observed that, there is no formation of Fe2+ ion even if the doping levels are as high as 30%, as it is expected that Fe3+ ion changes its valance to maintain the charge neutrality. However, there is an increase in s-electron density for number of sites with doping. Quadrupole splitting values shows spherical charge distribution for all the sublattices except 2b, due to asymmetric nature of bipyramidal site. Slightly varied magnetic hyperfine splitting values are observed for 12 k and 4f1 sites shows the effect of La substitution.

The phase composition and structure of the BiFeO-=SUB=-3-=/SUB=- film grown on MgO(001) substrate by high frequency cathode deposition in oxygen atmosphere

The crystal structure and Mossbauer spectroscopy studies results for BiFeO3 film growth on the MgO(001) single crystal substrate are present in the paper. It been shown that film have high crystal perfection and low defectiveness which results in appearing of narrow lines during the theta-2theta and φ scanning and the small (lower than 0.7o) disorientation of film and substrate crystal axes. It is been revealed that unit cell of BiFeO3/MgO(001) heterostructure possess monoclinic symmetry and deformation of unit cell is negligible. The Mossbauer study shows that magnetic subsystem of film has spatial spin-modulated structure with zero value of anharmonicity parameter (m). This indicate that at room temperature the magnetic anisotropy changes from the "easy axis" type to "easy plane" type. Keywords: thin films, bismuth ferrite, Mossbauer effect.

Фазовый состав и структура пленки BiFeO-=SUB=-3-=/SUB=-, выращенной на подложке MgO(001) методом ВЧ-катодного распыления в атмосфере O-=SUB=-2-=/SUB=-

The crystal structure and Mossbauer spectroscopy studies results for BiFeO3 film growth on the MgO(001) single crystal substrate are present in the paper. It been shown that film have high crystal perfection and low defectiveness which results in appearing of narrow lines during the θ-2θ and φ scanning and the small (lower than 0.7°) disorientation of film and substrate crystal axes. It is been revealed that unit cell of BiFeO3/MgO(001) heterostructure possess monoclinic symmetry and deformation of unit cell is negligible. The Mossbauer study shows that magnetic subsystem of film has spatial spin-modulated structure with zero value of anharmonicity parameter (m). This indicate that at room temperature the magnetic anisotropy changes from the "easy axis" type to "easy plane" type.

Characterization study and recovery of copper from low grade copper ore through hydrometallurgical route

Characterization studies were conducted on low grade copper ore with the aid of standard approaches. The Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) study specifies the semi-quantitative data of qualitatively analyzed chemical elements present in the ore sample. Optical Microscopy (OM) and X-Ray Diffraction (XRD) endorse the presence of chalcopyrite (CuFeS2) and pyrites along with other different mineral phases in the ore sample. Thermo Gravimetric Analysis (TGA) and Mossbauer spectroscopy studies confirm the formation of CuO and Fe2O3 after roasting at 700 °C. The better copper recovery from low grade copper ore was achieved through optimized leaching parameters. It was found that the particle size of −63+53 µm can be leached up to 94.96 % of copper using a lixiviant reagent mixture (30 vol. % hydrogen peroxide and 0.5 M sulfuric acid) under magnetic stirring for 30 min at a constant speed of 300 rpm, by keeping the liquid/solid (L/S) ratio at 20/2 ml/g. Moreover, the solvent extraction process works well with the pregnant leach solution, whereby, 98.9 % of copper extraction is possible, and the loading time is less than a minute. Meanwhile, 93.91 % of overall copper extraction efficiency was achieved through optimized leaching parameters and solvent extraction method.

Mossbauer and Raman spectroscopy study of Y-garnet particles’ magnetic properties tune-up through mechanochemically synthesized precursors

Mossbauer and Raman spectroscopy study of Y-garnet particles’ magnetic properties tune-up through mechanochemically synthesized precursors

From magnetic cluster glass state to giant vertical magnetization shift induced by ferromagnetic cluster growth in SrFe0.25Co0.75O2.63

A charge ordering phenomenon within the crystallographic sites as following Sr4(Fe0.143+Co0.363+)48h(Fe0.114+Co0.144+Co0.253+)48fO10.52 was previously reported thanks to neutron diffraction coupled with Mossbauer spectroscopy studies. Such distribution supports a natural magnetic layered structure combining both in-plane ferromagnetic super-exchange interactions mainly on the octahedron “8 f” sub-layer alternating and in-plane antiferromagnetic super-exchange interactions on the “8 h” sub-layer containing tetrahedral sites and five-fold symmetry polyhedra (i.e. squared based pyramid and/or trigonal bipyramid). Because of the interfacial magnetic interactions between the two types of layers, we report a detailed study of the intriguing magnetic properties. AC magnetic susceptibility shows a frequency dependent peak suggesting a cooperative character due to inter-cluster interactions resulting in a magnetic cluster glass state. When temperature decreases and/or applied magnetic field increase, the ferromagnetic clusters growth is promoted and results in a large vertical hysteretic shift on the Field Cooled magnetization isotherm in relation with minor loop.

Neutron Diffraction Magnetic and Mossbauer Spectroscopic Studies of Pb0.8Bi0.2Fe0.728W0.264O3 and Pb0.7Bi0.3Fe0.762W0.231O3 Ceramics

We report on high-temperature crystallographic structure, magnetic and physical properties of chemically B-site disordered lead-bismuth iron tungstate, (PFW)1−x(BFO)x (which can be written as Pb0.8Bi0.2Fe0.728W0.264O3 (0.8PFW–0.2BFO) for x = 0.2 and Pb0.7Bi0.3Fe0.762W0.231O3 (0.7PFW–0.3BFO) for x = 0.3) or PBFW), solid solutions through neutron diffraction (ND), magnetization, electron paramagnetic resonance, and Mössbauer spectroscopic studies. From the high temperature magnetic susceptibility measurement, it is observed that increase antiferromagnetic to paramagnetic phase transition around TN = 435 K (Pb0.8Bi0.2Fe0.728W0.264O3) and 504 K (Pb0.7Bi0.3Fe0.762W0.231O3), compared to pure PFW. Room-temperature crystallographic study confirms the formation of pseudo cubic structure with Pm-3m space group, whereas the magnetic structure is commensurate G-type antiferromagnetic ordering. The obtained temperature dependent structural parameters from the ND, evidenced to existence of strong spin-lattice coupling around TN for both the compounds. The discontinuity in the Pb/Bi–O bond length around ferroelectric transition (TC) indicates the presence of magnetoelectric coupling. Interestingly, microscopic 1:1 B-site ordered nanoclusters of PBFW exhibits the ferrimagnetic clusters along with antiferromagnetic order and it observed through the opening of M vs H hysteresis curves in the lower field regime. The EPR and Mössbauer spectroscopic studies well support the magnetic property and also reveal the Fe+3 state, and the weak signal in EPR and broader linewidth in the Mössbauer spectra exhibit the B-site disorderliness.

Mössbauer Study of Rare-earth Ferroborate NdFe3(BO3)4

An 57Fe Mossbauer spectroscopic study has been conducted on the single-crystal NdFe3(BO3)4 to investigate its magnetic structure and multiferroicity. In the multiferroic state below the Neel temper...

Weak ferromagnetism and magnetoelectric coupling through the spin–lattice coupling in (1−x)Pb(Fe2/3W1/3)O3–(x)BiFeO3 (x = 0.1 and 0.4) solid solution

We report on the structure, spin–lattice and magneto-electric coupling in (1−x)Pb(Fe2/3W1/3)O3–(x)BiFeO3(where x = 0.1 and 0.4) (PBFW) solid solution synthesized through two-step solid-state reaction method. The room temperature (RT) crystallographic studies were carried out using x-ray diffraction and neutron diffraction measurements which show a single-phase Pseudocubic crystal system with Pm-3m space group. Rietveld refinement was carried out to obtain the structural parameters using Fullprof software and the observed structural parameters are in good agreement with the previous reports. Temperature-dependent neutron diffraction measurements reveal the presence of commensurate G-type antiferromagnetic structure. The magnetic structure was analyzed using the propagation wave vector k ∼ (½ ½ ½) for both the solid solutions. The obtained lattice constants increase linearly and the magnetic moment decrease with temperature, which shows a remarkable anomaly around the magnetic (TN ∼ 405 K for x = 0.1 and 531 K for x = 0.4) transition temperatures. This anomaly clearly indicates the existence of spin–lattice and magnetoelectric coupling. The magnetic susceptibility (ZFC and FC at 500 Oe) and M–H hysteresis loop measurements show spontaneous magnetic moment due to the Fe3+–O2−–Fe3+ superexchange interaction coexisting with the weak ferromagnetism. Bifurcation of ZFC and FC curve reveals the strong anisotropic nature. Astonishingly, magnetic measurements show the non-zero magnetic moment above TN and broadening of the magnetic transition indicates the presence of short-range uncompensated sublattice weak ferromagnetic clusters in the paramagnetic region. The Mossbauer spectroscopy and electron paramagnetic resonance studies exhibit the RT magnetically ordered system and confirm the +3 state of Fe along with the fraction of Fe2+ ions.

Mössbauer Spectroscopy of Magnetic Nanoparticles: A Historical Perspective and State of the Art

Mossbauer spectroscopy is one of the main methods that are successfully applied to study the properties of magnetic nanoparticles (MNPs), because the small MNP size often of key importance for implementing various forms of absorption spectra of these materials. The results of experimental and theoretical Mossbauer spectroscopy studies of MNPs performed in the last 50 years are briefly discussed. The emphasis is on the mechanisms of formation of the magnetic hyperfine structure of spectra within the models of magnetic dynamics of nanoparticles of different magnetic nature.

Mossbauer studies of BiFeO3 Mulitiferroic nanoparticles doped with Eu

This work presents the results of BiFeO3 and Bi0.9Eu0.1FeO3 multiferroic materials, synthesized via a simple solid-phase reaction method. Both of the synthesized materials were in the rhombohedral R3c structure as observed by X-ray diffraction (XRD). The presence of a doublet along with a sextet in Mossbauer spectra indicates an impurity phase (Bi2Fe4O9). The presence of Fe2+ ions are confirmed from Mossbauer spectroscopy study in the Bi0.9Eu0.1FeO3 sample. And the Bi0.9Eu0.1FeO3 exhibited a slight lattice distortion, observable from the results of XRD and Mossbauer spectra. We can conclude that growing of crystal homogeneity of Bi0.9Eu0.1FeO3 is better than BiFeO3.

Mössbauer spectroscopy study of Y-type Hexaferrite (Ba2Co2Fe12O22) prepared by the co-precipitation method

In this work we report the results of structural and Mossbauer spectroscopy studies for Ba2Co2Fe12O22 samples prepared by coprecipitation following two different synthesis routes: route A (pH = 10, NaOH + Na2CO3 added dropwise), and route B (pH = 14, NaOH + Na2CO3 added one shot). The resulting powders were sintered for 4 h at different temperatures (700 °C to 1100 °C in steps of 100 °C). The sintered powders were characterized by x-ray diffraction (XRD) and room temperature Mossbauer spectroscopy. XRD and Mossbauer results of the sample prepared by route A and sintered at 700 °C revealed formation of spinel phases (CoFe2O4 and/or Fe3O4), BaCO3 and BaM-type phase. The Co2Y phase developed in the samples sintered at 800 °C and 900 °C with spinel species as impurities, and single (pure) Co2Y phase was obtained at higher temperatures. On contrast, XRD patterns and the Mossbauer spectra for the samples prepared by route B showed different results, where the sample sintered at 700 °C consisted of only spinel phases. The Co2Y phase developed at higher temperatures, coexisting with significant amounts of other phases.

Mössbauer Spectroscopy Study of KxFe2−ySe2 under Pressure

A Mossbauer spectroscopy study of the iron-based superconductor KxFe2−ySe2, with two superconducting phases of SC1 and a pressure induced SC2 was performed under pressure. This compound consists of...

Mechanism of formation of framework Fe3+ in bimetallic Ag-Fe mordenites - Effective catalytic centers for deNOx reaction

Abstract As it was reported in our previous study (P. Sanchez-Lopez et al., 2019), mono- and bimetallic systems of Ag, Fe, and Ag-Fe supported on mordenites exhibit a nontrivial dependence of deNOx activity from the preparation procedure. In this work we report on the results of our comprehensive study of the sample composition, structure and morphology to reveal issues of the observed synergetic effect. It was found that both the order of the ion exchange reactions and processing temperature affect the distribution and state of silver and iron species in the mordenite matrix. In the Ag-containing samples silver is accumulated on the surface in the form of X-ray amorphous nanoparticles of 2–10 nm in size; however, charge compensating Ag+ cations are also present. The Mossbauer spectroscopy study of the iron-containing samples evidences the isomorphous substitution of Al3+ by Fe3+ in the mordenite framework. The portion of this framework Fe3+ correlates with catalytic deNOx activity of the studied materials. Hydrated extra-framework Fe2+ cations are Mossbauer silent at room temperature, but their presence is evident from the increasing of the a/b ratio caused by the contraction of the main mordenite channel upon iron cations loading. Based on the reported results we propose a mechanism of the isomorphous substitution of the framework Al3+ by Fe3+ promoted by Ag+. This mechanism leads to creation of new effective catalytic centers for deNOx reaction, which are (i) framework Fe3+ activated by nearby Ag+ and (ii) a very few nanosized Ag particles on the Fe-mordenite surface.

Fe3C nanoparticle formation in Fe implanted HOPG and CVD diamond

We have conducted conversion electron Mossbauer spectroscopy (CEMS) studies of Fe-carbides produced in Fe implanted highly oriented pyrolytic graphite (HOPG) and CVD diamond substrates. The samples were implanted at room temperature with 57Fe ions with 40 keV and 60 keV, respectively, and corresponding fluences of 1.0·1016/cm2 and 5·1015/cm2. The formation of magnetic structures in the spectra was monitored with CEMS measurement after annealing the samples at temperatures up to 700 °C. After the high temperature annealing, the main components in the spectra were sextets whose line shapes displayed strong, asymmetric distortions, consistent with those due the formation of nanoclusters. The hyperfine magnetic fields Bhf = 21.6 T, 20.0 T and 18 (1) T were in good agreement with those observed previously for Fe3C nanoclusters 10–20 nm in size.

Local Structure and Magnetic Structure of Spinel Oxide MnV2O4 Observed by Mössbauer Spectroscopy

Mossbauer spectroscopic study has been conducted on a spinel oxide MnV2O4 by using a 1 mol % 57Fe-substituted polycrystalline specimen as an absorber. The substituted 57Fe ions occupy both the A- a...

Magnetite and the Verwey transition, from γ-rays to low-energy electrons

Magnetite, a semiconducting ferrimagnetic iron spinel with a metal-insulator phase transition, the Verwey transition, has long been the subject of Mossbauer spectroscopy studies, which continue today. We review the current status of the understanding of the Mossbauer spectra of magnetite. Furthermore, magnetite is a very attractive material in current topics such as spintronics. In this particular subject, to determine the behavior of magnetic domains is paramount, and the changes ocurring on the near surface region upon undergoing the Verwey transition are relevant. In order to advance in this area, we have incorporated some new techniques, namely microscopy observations made with low-energy electrons. These observations can be performed upon changing the temperature, and can provide magnetic contrast through the use of spin-polarized electrons. By this means, we have observed the ferroelastic transformation associated with the Verwey transition, discovered an order-disorder transition of the (001) surface of magnetite and observed the changes in the magnetic domains on the same surface by changing the temperature. Low-energy electrons also are the key to the Mossbauer experiments of magnetite films and surfaces, with the promise of providing surface-sensitive spatially resolved Mossbauer spectra.

Shifting from Ising model to Heisenberg model critical behavior and the departure from these models in Fe73.5−Cr Cu1Nb3Si13.5B9

Abstract The universality classes of amorphous alloy system Fe73.5−xCrxCu1Nb3Si13.5B9 with x = 0, 2, 4, 6, 8, and 10 are studied by determination of the static critical exponents (β, γ, δ), and critical temperatures from magnetization measurements using two independent methods, namely the Kouvel-Fisher method and the Berger-Campillo et al method. The found values for these critical exponents depend on the content of Cr and interestingly vary from values that correspond to universality classes of standard models (Ising (sample with x = 0), XY (sample with x = 2), and Heisenberg (sample with x = 4)) with short-range interactions to universality class of mean field model (samples with x = 6, 8, and 10) with long-range interactions. The critical temperature decreases quasi linearly with the increase of Cr content. The possible mechanisms leading to such universality classes and shift including the spin-orbit interaction, shape anisotropies, direct exchange and itinerant exchange are analyzed. In addition, X-ray diffraction and Mossbauer spectroscopy studies performed on this alloy system reveal that it has a heterogeneous structure.