Mossbauer Measurements Research Articles

Structural, electronic, and magnetic study on hematite nanorods: Effect of carbon coating and annealing temperature

In this work, spindle shape α-Fe2O3 nanorods and carbon-coated α-Fe2O3@C nanorods were synthesized using a simple hydrothermal method followed by calcination at a temperature of 600 °C. Morphology, structural, surface, and magnetic properties of the synthesized samples were studied before and after calcination. XRD results prove the formation of a single corundum phase α-Fe2O3 after hydrothermal preparation at 180 °C. The crystallite size of α-Fe2O3 decreases by calcination in contrast with α-Fe2O3@C. Through calcination, meso-size pores were formed as investigated by TEM. These pores are more in α-Fe2O3 nanorods. Using XPS surface analysis, more O-H bonds were found in α-Fe2O3 nanorods. TEM, XPS, and FTIR techniques were used to prove the formation of the Carbon layer on α-Fe2O3@C nanorods. Intensive characterization and the magnetic properties of α-Fe2O3 and α-Fe2O3@C nanorods were also carried out and reported. VSM measurements show an increase in magnetic moment with smaller coercivity and remanence via C-coating and calcination. The Morin transition as investigated using VSM and Mossbauer measurements, appears for pure hematite nanorods after calcination under atmospheric pressure. This transition is suppressed as shown for nanosize particles with c/a of ≥ 2.74 which was also applicable for samples made by other workers.

MOSSBAUER AND X-RAY FLUORESCENCE STUDIES OF FLY ASH BASED PROPPANTS

This article discusses the results of the study of proppants obtained from domestic raw materials - bauxite, kaolin and white clay, sand, as well as fly ash by nuclear gamma resonance spectroscopy (the Mossbauer effect) and X-ray fluorescence analysis. The hyperfine structure, electronic states and elemental composition of proppants are given. The results of the study of volatile ash obtained during pulverized coal burning of Ekibastuz, Shubarkul, Karazhyralinsky deposits at thermal power plants are analyzed. According to the results of the studies, various combinations of complex phases and the elemental composition of proppants were determined using Mossbauer spectroscopy and X-ray fluorescence analysis. The Mossbauer measurements were carried out on the MS1104Em spectrometer in the constant acceleration mode with a 57Co source in a chromium matrix at room temperature. The elemental composition of samples of proppants based on fly ash was determined using an energy dispersive X-ray fluorescence spectrometer (RFS) at the EDX-7000 installation of SHIMADZU.

Nanowires Made of FeNi and FeCo Alloys: Synthesis, Structure, and Mössbauer Measurements

Nanowires have been formed from FeNi and FeCo alloys by the template synthesis method based on galvanic filling of pores of track membranes. A change in the nanowire elemental composition with a change in the electrolyte composition and with a change in the deposition potential has been studied. FeNi nanowires exhibit the effect of anomalous Fe codeposition: the iron content in the nanowires is much higher than that in the electrolyte. The difference increases with an increase in the initial concentration and with a decrease in the growth potential. It has also been found that the iron concentration increases in nanowire vertices. For FeCo nanowires, their composition corresponds to the electrolyte composition and changes only slightly with a change in the potential. An analysis of the X-ray diffraction data has determined the character of change in the spectra under varying growth conditions. The X-ray spectra of FeNi are found to depend on the growth potential (the intensity of phase peaks changes). Mossbauer measurements have revealed spontaneous magnetization for all samples of arrays of nanowires along their axes. The dependence of hyperfine magnetic field strength Bhf at 57Fe nuclei on the composition of nanowires of FexCo1 – x and FexNi1 – x solid solutions is obtained for the first time. It is found that the Bhf value decreases with an increase in the electrodeposition rate (or with an increase in deposition potential U).

Magnetic phase transitions in Eu( Co1−xNix)2−yAs2 single crystals

The effects of Ni doping in Eu(Co{1-x}Ni{x})2As2 single crystals with x =0 to 1 grown out of self flux are investigated via crystallographic, electronic transport, magnetic, and thermal measurements. All compositions adopt the body-centered-tetragonal ThCr2Si2 structure with space group I4/mmm. We also find 3-4% of randomly-distributed vacancies on the Co/Ni site. Anisotropic magnetic susceptibility chi(T) data versus temperature T show clear signatures of an antiferromagnetic (AFM) c-axis helix structure associated with the Eu{+2} spins-7/2 for x = 0 and x = 1 as previously reported. The chi(T) data for x = 0.03 and 0.10 suggest an anomalous 2q magnetic structure containing two helix axes along the c axis and in the ab plane, respectively, whereas for x = 0.75 and 0.82, a c-axis helix is inferred as previously found for x = 0 and 1. At intermediate compositions x = 0.2, 0.32, 0.42, 0.54, and 0.65 a magnetic structure with a large ferromagnetic (FM) c-axis component is found from magnetization versus field isotherms, suggested to be an incommensurate FM cone structure associated with the Eu spins, which consists of both AFM and FM components. In addition, the chi(T) and heat capacity data for x = 0.2--0.65 indicate the occurrence of itinerant FM order associated with the Co/Ni atoms with Curie temperatures from 60 K to 25 K, respectively. Electrical resistivity measurements indicate metallic character for all compositions with abrupt increases in slope on cooling below the Eu AFM transition temperatures. In addition to this panoply of magnetic transitions, {151}Eu Mossbauer measurements indicate that ordering of the Eu moments proceeds via an incommensurate sine amplitude-modulated structure with additional transition temperatures associated with this effect.

Photo-Fenton degradation of methylene blue using hematite-enriched slag under visible light

This study aims to find a suitable method to transform the amorphous iron oxides obtained from the incineration of combustible waste slag into hematite. The resulting samples were utilized as heterogeneous photocatalysts for the photo-Fenton degradation of methylene blue (MB) aqueous solution. A good correlation was found between the MB degradation and the amount of hematite phase as confirmed by XRD and Mossbauer measurements. The largest rate constant (k) was (4.1 ± 0.08) × 10−2 min−1 for MB decomposition under visible-light for the sample N5-50-800. The results are promising for both low-cost photocatalysts and recycling of combustible waste slags.

Effect of cation distribution on the structural and dielectric properties of $${\mathrm{N}\mathrm{i}}_{0.5-x}{\mathrm{C}\mathrm{o}}_{x}{\mathrm{Z}\mathrm{n}}_{0.5}{\mathrm{F}\mathrm{e}}_{2}{\mathrm{O}}_{4}$$ (0.0 ≤ x ≤ 0.5) ferrites

Cobalt-substituted nickel–zinc ferrite nanoparticles, i.e., $${\mathrm{N}\mathrm{i}}_{0.5-x}{\mathrm{C}\mathrm{o}}_{\mathrm{x}}{\mathrm{Z}\mathrm{n}}_{0.5}{\mathrm{F}\mathrm{e}}_{2}{\mathrm{O}}_{4}$$ (0.0 ≤ x ≤ 0.5) were prepared by the sol–gel method. X-ray diffraction patterns revealed that the prepared samples crystallized in cubic spinel structure, whereas the scanning electron microscopy study exhibited a change in the morphology of grains due to Co2+ substitution. 57Fe Mossbauer measurements suggested that the presence of iron is only in the Fe3+ oxidation state which is randomly distributed over the tetrahedral and octahedral sites. However, the fraction of Fe3+ ions present at the octahedral site strongly depends on the unusual site preference of substituted Co2+ ions for the tetrahedral site. Thus, the cationic distribution between both the sites altered with increasing Co2+ substitution. Significant enhancement in the resistive properties is found with increasing Co2+ substitution and the obtained values are ~ 104 times higher than that reported for their bulk counterparts. This improvement in the resistive properties is elucidated based on changes in the microstructure and cation redistributions due to Co2+ substitution. Here, we report that the colossal resistivity (3.82 × 1010 Ω cm) and diminished tangent loss (~ 0.01) for the sample with x = 0.2 make this composition interesting for high-frequency applications.

57-Fe Mössbauer and magnetic studies of a new diphosphate Zn5Fe2(P2O7)4

Fe2+ ions in Fe7(P2O7)4 were substituted by Zn2+and the magnetic properties and Mossbauer spectra of the new material were studied. The obtained sample of Zn5Fe2(P2O7)4 is isostructural with the parent Fe7(P2O7)4, which is orthorhombic with a C2221 space group. Magnetometry shows that the Neel temperature is TN = 15.4(1) K, which is in accordance with Mossbauer measurements performed at RT and 4.2 K.

Magnetic properties and thermal stability of polyvinylidene fluoride—Fe2O3 nanocomposites

Abstract

Magnetization and room temperature Mössabuer studies of 50Fe2O3-50SiO2 and 90Fe2O3-10SiO2 ceramic fibers processed by laser floating zone method

In this work, we employed the Laser Floating Zone (LFZ) method to grow the ceramic fibers with composition of 50Fe2O3-50SiO2 and 90Fe2O3-10SiO2, with two different pulling rates: 25 and 200 mm/h. The physical properties of the ceramics were studied as the function of the iron oxide content and the pulling rate. XRD analysis depicted that the main crystalline phase formed in all samples is magnetite. Although, the appearance of small quantity of nano-crystalline fayalite was also confimed. From the magnetic measurements, a Verwey transition for all LFZ fibers in the temperature range varying from 100 to 115 K depending on the composition and the pulling rate, was observed. Room temperature 57-Fe Mossbauer measurements showed that the degree of non-stoichiometry of LFZ ceramics with 90% of the iron content is higher than one for LFZ samples containing 50% of iron oxide. A great agreement was obtained between the result of Mossbauer spectroscopy measurements and VSM studies. The revealed behaviours can be described in terms of the temperature dependent interactions occurring between the magnetic clusters formed in the fibres.

Electronic and atomic dynamics in Sm and Eu cage-structured intermetallics

Mossbauer measurements using both synchrotron radiation and radioactive sources were performed on Sm and Eu cage-structured compounds. Such measurements reveal electronic states through hyperfine interactions at probe nuclei and lattice dynamics through Mossbauer effects of probe nuclei. We have reviewed recent results of the cage-structured compounds SmB6, SmBe13, SmOs4Sb12 and Eu3Pd20Ge6 obtained by synchrotron-radiation-based and conventional Mossbauer spectroscopy and nuclear resonant inelastic scattering experiments.

Microstructural and magnetic properties of Zn substituted nickel ferrite synthesised by facile solution combustion method

This work reports the synthesis of Ni 1-x Zn x Fe 2 O 4 ferrite (where x = 0, 0.1, 0.3, and 0.5) by a facile solution combustion method, using oxalyl-dihydrazide as a fuel. Owing to stoichiometric mixing of the starting materials and dissipation of heat during the combustion process, nano-sized spinel ferrites have been synthesised. Fourier transform infrared spectroscopy studies were carried out to confirm the presence of metal-oxide bands in spinel ferrites. X-ray powder diffraction analysis confirmed the presence of a single phase cubic nanocrystalline nature of ferrite samples. Energy dispersive X-ray spectroscopy studies showed the purity of ferrite samples. The effect of Zn substitution on the magnetic properties of these ferrites is also reported here. Magnetic studies revealed that the saturation magnetisation for these ferrite powders increases up to x = 0.3 (38.73 emu/g) and then decreases. Mossbauer measurements revealed a gradual transition from a ferrimagnetic to a superparamagnetic character with increasing concentration of Zn.

Synthesis and Study of (Sr,La)2FeCo0.5Mo0.5O6 − δ Oxides with Double Perovskite Structure

Complex oxides Sr2 − xLaxFeCo0.5Mo0.5O6 − δ, (x = 0.2, 0.4; δ ≈ 0.03–0.15) have been first synthesized by the sol-gel method. Their crystal structures have been refined by the Rietveld method; the refinement showed that the complex oxides have the structure of cubic double perovskite (a ≈ 2aper, space group Fm3m) with partial ordering of Fe(Co) and Mo in the B positions. Based on the 57Fe Mossbauer measurements, the average formal oxidation state of iron has been found to decrease from +3.20 (x = 0.0) to +3.04 (x = 0.4). Our study of the behavior of perovskites in a reducing Ar/H2 atmosphere (8%) revealed a decrease in the reduction resistance with decreasing La content (x = 0.4 → 0). The combination of the properties studied, namely chemical stability with respect to the reaction with Ce1 − xGdxO2 − x/2 and Zr1 − xYxO2 − x/2, high-temperature thermal expansion, and electrical conductivity in air and Ar/H2, shows that Sr1.6La0.4Fe-Co0.5Mo0.5O6 − δ (δ ≈ 0.03) perovskite is more attractive as an electrode material for medium-temperature symmetric solid oxide fuel cells than Sr2FeCo0.5Mo0.5O6 − δ.

Mössbauer, Magnetization and Structure Characterizations of the Annealed Sr1/3Mn1/3Co1/3Fe2O4 Ferrite Nanoparticles

Sr1/3Mn1/3Co1/3Fe2O4 ferrite nanoparticles were synthesized by glycol thermal technique. The structure and morphology of the Nano ferrites were studied by X-ray powder diffraction, Fourier transform infrared FTIR, high-resolution scanning electron microscopy, and high-resolution transmission electron microscopy. The induced internal strains were investigated by Williamson plots. The results show mono-dispersive property of the sample and particle sizes that increase with increasing annealing temperature, TA. The magnetic hyperfine fields were found to be sensitive to TA as seen from room temperature 57Fe Mossbauer measurements. The magnetic hysteresis loops were performed in external magnetic field of up to 50 kOe. Room temperature M − H loops showed that the coercive fields increased to a maximum at TA of 500 °C and then decreased thereafter. Significant increases in coercive fields were observed at a measuring temperature of 4 K. Distortions in the hysteresis loops at 4 K were observed where thermal annealing effect appears to induce strong linear correlation between coercive fields and saturation magnetizations.

Multistep Development of the Hyperfine Fields in λ-(BEDT-STF)2FeCl4 Studied by Mössbauer Spectroscopy

We have investigated the magnetic properties of λ-(BEDT-STF)2FeCl4 by Mossbauer measurement to reveal the origin of the paramagnetic-like behavior of the 3d spin system observed in λ-(BETS)2FeCl4 u...

Magnetic Properties and Mössbauer Studies of Fe3O4 Substituted with Gd Ions

The Gd0.05Fe2.95O4 nanoparticles were synthesized by seed - mediated growth and were reacted for 30, 45, 60 and 75 min (Gd30, Gd45, Gd60 and Gd75), respectively. The samples structural and magnetic properties were investigated by x-ray diffraction (XRD), vibrating sample magnetometry (VSM), and Mossbauer spectroscopy. The self-heating properties were investigated by using a MagneTherm device. According to XRD analysis, gadolinium (Gd) nanoparticles found to be a cubic spinel structure has a space group Fd-3m. The lattice constant (a0) of Gd nanoparticles are 8.3633 ˚A and increases to 8.3721 ˚A as the high-temperature reaction time increases. The particle size was determined using Scherrer’s equation and the maximum particle size was 10.84 nm. The maximum saturation magnetization (MS) value of Gd60 at room temperature was 63.10 emu/g. The self - heating temperature of Gd60 at 112 kHz and 250 Oe was measured and 63.3 °C was the highest. Gd60 had the largest particle size and highest MS and self-heating properties were measured. Mossbauer measurements were performed to investigate hyperfine interactions at from 4.2 to 290 K.

Formation of Phases upon the Mechanosynthesis and Subsequent Annealing of Samples of Cementite Composition Alloyed with Chromium and Nickel

Using X-ray, Mossbauer, and magnetic measurements, the formation of phases has been investigated upon mechanosynthesis in a ball planetary mill and upon the subsequent annealing of samples of the cementite composition (Fe0.95–уСr0.05Ni y )75C25, where у = 0–0.20, which contains two alloying elements (chromium and nickel). It has been shown that, in the mechanosynthesis process, cementite alloyed with chromium and a small amount of nickel and an amorphous phase alloyed with chromium and nickel have been formed. Upon heating above 300°С, the amorphous phase is crystallized into nickel-enriched cementite. In the process of annealing at higher temperatures, the most nickel-rich cementite decomposes with the formation of austenite. As a consequence, after annealing at medium temperatures, the composition of the alloys contains cementite alloyed mainly with chromium and some amount of alloyed austenite, which can be found in ferromagnetic or paramagnetic states depending on the Ni content. Annealing at 800°С bring about the complete or partial decomposition of cementite contained in the alloys. The intensity of the decomposition has been determined by the nickel content in the samples.

Rietveld refinement, morphology and superparamagnetism of nanocrystalline Ni0.70−xCuxZn0.30Fe2O4 spinel ferrite

The crystallographic phase and particle size of Cu2+ substituted Ni-Zn spinel ferrite prepared by nitrate-citrate route was evaluated using XRD and TEM techniques respectively. Rietveld refined XRD patterns revealed the cubic spinel phase with Fd-3m space group. The average particle size estimated from TEM image revealed the nanocrystalline nature which matches well with the crystallite size determined by XRD data. High resolution TEM exhibited the lattice fringe patterns which correspond to cubic spinel structure. The samples were characterized by M-H plots and Mossbauer spectra at room temperature. Magnetization curves exhibited typical superparamagnetic nature of samples which is in good agreement with that of Mossbauer measurements. The obtained coercive field is low which may make these materials suitable for soft magnetic device applications.

Stability and Local Environment of Iron in Vapor Phase Grown MgO Nanocrystals

Metallocene injection into a metal combustion flame has been used for trapping transition metal ions inside MgO nanocrystals. Vacuum annealing changes the properties of resulting nonequilibrium solids toward thermodynamic equilibrium and provides means to control impurity localization and, as a result, the nanomaterials’ functional properties. By combining structure characterization (X-ray diffraction and transmission electron microscopy) with X-ray absorption spectroscopy and Mossbauer measurements, we tracked valence state and local chemical environment changes of Fe3+ ions inside vapor phase synthesized MgO nanocrystals. At a concentration of (1.5 ± 0.2) at. % Fe about (1400 ± 200) Fe3+ ions are effectively diluted within 12 nm sized nanocubes, where they form complexes between Fe3+ ions and Mg2+ vacancies. Increase of the iron concentration produces additional effects: enhanced ion diffusion and particle coarsening at elevated temperatures, clustering of Fe3+–Mg2+ vacancy complexes and, after annealin...

Facile synthesis of highly dispersed Fe(II)-doped g-C3N4 and its application in Fenton-like catalysis

In this work, highly dispersed Fe(II)-doped g-C3N4 was successfully prepared by simple calcination of a Fe+3/melamine precursor in a semi-closed alumina crucible at 550°C without atmosphere protection. The morphology, structure, and chemical composition of the products were characterized fully. Thermogravimetric analysis/Differential thermic analysis (TGA/DTA), 57Fe Mossbauer, and electron paramagnetic resonance measurements were used to evaluate the changes in the chemical composition of the 10%-Fe/melamine precursor as a function of the calcination temperature, revealing that reduction of Fe+3 to Fe+2 occurs progressively at temperatures between 310°C and 550°C. The prepared Fe-doped g-C3N4 materials exhibit high activity in the Fenton-like degradation of cationic methylene blue within a wide pH range, as well as high reusability and low iron leaching. The catalysts display high activity in the degradation of cationic rhodamine B, anionic indigo carmine (IC), and neutral phenol. Electrospray ionisation mass spectrometry (ESI-MS) measurements confirmed that all selected substrates were successively oxidized into different intermediate compounds before mineralization, exhibiting great potential for application in the degradation of environmental pollutants.

57 Fe Mössbauer study of spin reorientation transition in polycrystalline NdFeO 3

Abstract The present work reports the preparation of polycrystalline NdFeO 3 using sol-gel method and characterization using X-ray diffraction (XRD), Raman spectroscopy, bulk magnetization, 57 Fe Mossbauer spectroscopy and ferroelectric measurements. XRD and Raman spectroscopy measurements confirm the phase purity of the prepared sample. The temperature dependent magnetization measurement shows the signatures of spin re-orientation transition ( T SRT ) between 66 and 158 K and magnetic field induced transition at about 2.5 T and 5 K. It is observed from the low temperature (25–300 K) 57 Fe Mossbauer measurements that the temperature variation of hyperfine parameters shows the signatures of T SRT . The observed area ratio of second and third line intensity (A 23 ) in Mossbauer sextet, across T SRT , show deviations from the value characteristic of random spin orientation in polycrystalline sample. In addition, the quadrupole shift changes sign across T SRT indicating the spin-reorientation of Fe 3+ ions. The room temperature leakage current density ( J - E ) measurements indicate that Ohmic contribution and space charge limited conduction are the dominating mechanisms at low and high applied electric fields, respectively, similar to that of other RFeO 3 (R – rare earth) based compounds. Lossy ferroelectric loops were observed at room temperature.